TL
Tim Lister
Tue, Oct 4, 2022 10:31 PM
Hi everyone, wanting to pick the collective brains of the group
regarding the use of dual frequency GPS antenna/receivers for NTP time
servers. I work for an observatory that runs telescopes at various
locations around the world and we had previously used Symmetricomm
S250 and S300 NTP time servers to allow remote management and to
provide NTP and IRIG-B signals but these are now affected by the Week
Number Roll Over problem. With the lowering cost of dual frequency
L1/L2 GPS receivers and antennas, I was thinking it would be nice to
have a (likely separate) dual frequency receiver to allow estimation
of the precipitable water vapor above the observatory. Timing
precision needed for the NTP signals is the ~2-3ms expected over local
Ethernet and ~20-50us for a 1PPS output for the future; commercial
solutions rather than homebrew strongly preferred for the time server.
So assuming that there aren't dual frequency time servers or a great
deal of benefit of dual frequency receivers in a time server for this
needed time precision:
- Is putting a 2 way splitter in front on the time server to split
the GPS signal for the time server and the experimental dual frequency
receiver going to cause issues ? Are there recommended 2 way splitters
that pass L1 and L2 well ?
- Any recommendations for good quality but not insanely expensive
L1/L2 antenna that will survive being on a pole on a remote high
mountaintop for ~decade ?
Thanks for any input,
Tim
Hi everyone, wanting to pick the collective brains of the group
regarding the use of dual frequency GPS antenna/receivers for NTP time
servers. I work for an observatory that runs telescopes at various
locations around the world and we had previously used Symmetricomm
S250 and S300 NTP time servers to allow remote management and to
provide NTP and IRIG-B signals but these are now affected by the Week
Number Roll Over problem. With the lowering cost of dual frequency
L1/L2 GPS receivers and antennas, I was thinking it would be nice to
have a (likely separate) dual frequency receiver to allow estimation
of the precipitable water vapor above the observatory. Timing
precision needed for the NTP signals is the ~2-3ms expected over local
Ethernet and ~20-50us for a 1PPS output for the future; commercial
solutions rather than homebrew strongly preferred for the time server.
So assuming that there aren't dual frequency time servers or a great
deal of benefit of dual frequency receivers in a time server for this
needed time precision:
1) Is putting a 2 way splitter in front on the time server to split
the GPS signal for the time server and the experimental dual frequency
receiver going to cause issues ? Are there recommended 2 way splitters
that pass L1 and L2 well ?
2) Any recommendations for good quality but not insanely expensive
L1/L2 antenna that will survive being on a pole on a remote high
mountaintop for ~decade ?
Thanks for any input,
Tim
JA
John Ackermann N8UR
Tue, Oct 4, 2022 11:08 PM
Hi Tim --
See below.
On 10/4/22 18:31, Tim Lister via time-nuts wrote:
Hi everyone, wanting to pick the collective brains of the group
regarding the use of dual frequency GPS antenna/receivers for NTP time
servers. I work for an observatory that runs telescopes at various
locations around the world and we had previously used Symmetricomm
S250 and S300 NTP time servers to allow remote management and to
provide NTP and IRIG-B signals but these are now affected by the Week
Number Roll Over problem. With the lowering cost of dual frequency
L1/L2 GPS receivers and antennas, I was thinking it would be nice to
have a (likely separate) dual frequency receiver to allow estimation
of the precipitable water vapor above the observatory. Timing
precision needed for the NTP signals is the ~2-3ms expected over local
Ethernet and ~20-50us for a 1PPS output for the future; commercial
solutions rather than homebrew strongly preferred for the time server.
So assuming that there aren't dual frequency time servers or a great
deal of benefit of dual frequency receivers in a time server
I think that's a good assumption. Even a single frequency GPS can
easily be accurate and stable to <100 ns. If you're using standard
computer hardware the latency and jitter of IRQ handling and CPU
overhead is far more than that. The improvement from a dual-frequency
receiver isn't going to be noticeable in that application.
- Is putting a 2 way splitter in front on the time server to split
the GPS signal for the time server and the experimental dual frequency
receiver going to cause issues ? Are there recommended 2 way splitters
that pass L1 and L2 well ?
Most GPS receivers these days have extremely sensitive front ends and
there's no magic required for a splitter -- many people have used cable
or satellite TV splitters with good results. You do need to worry about
the DC path so that the LNA at the antenna gets power, and none of the
receivers sees a DC short on its antenna input, but that's pretty
straightforward.
With dual frequency systems you do need to pay some attention to the
frequency response of the system since the signals are separated by ~300
MHz. And you need to make sure the splitter doesn't have any filtering
that will pass L1 but not L2 -- most "real" GPS splitters are L1 only.
- Any recommendations for good quality but not insanely expensive
L1/L2 antenna that will survive being on a pole on a remote high
mountaintop for ~decade ?
Historically L1/L2 antennas have in fact been insanely expensive, but
that's starting to change. u-blox sells a mini-hockey-puck mag mount
L1/L2 antenna for ~$100 IIRC, and there is at least one Chinese eBay
source for L1/L2/L5 "base" antennas for ~$200. Both of those will work
just fine for timing, though they don't have the precise phase center
needed for geodetic measurements.
Hope this helps!
John
Hi Tim --
See below.
On 10/4/22 18:31, Tim Lister via time-nuts wrote:
> Hi everyone, wanting to pick the collective brains of the group
> regarding the use of dual frequency GPS antenna/receivers for NTP time
> servers. I work for an observatory that runs telescopes at various
> locations around the world and we had previously used Symmetricomm
> S250 and S300 NTP time servers to allow remote management and to
> provide NTP and IRIG-B signals but these are now affected by the Week
> Number Roll Over problem. With the lowering cost of dual frequency
> L1/L2 GPS receivers and antennas, I was thinking it would be nice to
> have a (likely separate) dual frequency receiver to allow estimation
> of the precipitable water vapor above the observatory. Timing
> precision needed for the NTP signals is the ~2-3ms expected over local
> Ethernet and ~20-50us for a 1PPS output for the future; commercial
> solutions rather than homebrew strongly preferred for the time server.
>
> So assuming that there aren't dual frequency time servers or a great
> deal of benefit of dual frequency receivers in a time server
I think that's a good assumption. Even a single frequency GPS can
easily be accurate and stable to <100 ns. If you're using standard
computer hardware the latency and jitter of IRQ handling and CPU
overhead is far more than that. The improvement from a dual-frequency
receiver isn't going to be noticeable in that application.
> 1) Is putting a 2 way splitter in front on the time server to split
> the GPS signal for the time server and the experimental dual frequency
> receiver going to cause issues ? Are there recommended 2 way splitters
> that pass L1 and L2 well ?
Most GPS receivers these days have extremely sensitive front ends and
there's no magic required for a splitter -- many people have used cable
or satellite TV splitters with good results. You do need to worry about
the DC path so that the LNA at the antenna gets power, and none of the
receivers sees a DC short on its antenna input, but that's pretty
straightforward.
With dual frequency systems you do need to pay some attention to the
frequency response of the system since the signals are separated by ~300
MHz. And you need to make sure the splitter doesn't have any filtering
that will pass L1 but not L2 -- most "real" GPS splitters are L1 only.
> 2) Any recommendations for good quality but not insanely expensive
> L1/L2 antenna that will survive being on a pole on a remote high
> mountaintop for ~decade ?
Historically L1/L2 antennas have in fact been insanely expensive, but
that's starting to change. u-blox sells a mini-hockey-puck mag mount
L1/L2 antenna for ~$100 IIRC, and there is at least one Chinese eBay
source for L1/L2/L5 "base" antennas for ~$200. Both of those will work
just fine for timing, though they don't have the precise phase center
needed for geodetic measurements.
Hope this helps!
John
BK
Bob kb8tq
Tue, Oct 4, 2022 11:57 PM
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the server
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
If you do go with a dual freq GPS, you can do a very good job of working
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual freq
GPS data to correct against.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
Lots of tradeoffs.
Bob
On Oct 4, 2022, at 6:31 PM, Tim Lister via time-nuts time-nuts@lists.febo.com wrote:
Hi everyone, wanting to pick the collective brains of the group
regarding the use of dual frequency GPS antenna/receivers for NTP time
servers. I work for an observatory that runs telescopes at various
locations around the world and we had previously used Symmetricomm
S250 and S300 NTP time servers to allow remote management and to
provide NTP and IRIG-B signals but these are now affected by the Week
Number Roll Over problem. With the lowering cost of dual frequency
L1/L2 GPS receivers and antennas, I was thinking it would be nice to
have a (likely separate) dual frequency receiver to allow estimation
of the precipitable water vapor above the observatory. Timing
precision needed for the NTP signals is the ~2-3ms expected over local
Ethernet and ~20-50us for a 1PPS output for the future; commercial
solutions rather than homebrew strongly preferred for the time server.
So assuming that there aren't dual frequency time servers or a great
deal of benefit of dual frequency receivers in a time server for this
needed time precision:
- Is putting a 2 way splitter in front on the time server to split
the GPS signal for the time server and the experimental dual frequency
receiver going to cause issues ? Are there recommended 2 way splitters
that pass L1 and L2 well ?
- Any recommendations for good quality but not insanely expensive
L1/L2 antenna that will survive being on a pole on a remote high
mountaintop for ~decade ?
Thanks for any input,
Tim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a *lot* on what the next level source going into the server
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
If you *do* go with a dual freq GPS, you can do a very good job of working
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual freq
GPS data to correct against.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
Lots of tradeoffs.
Bob
> On Oct 4, 2022, at 6:31 PM, Tim Lister via time-nuts <time-nuts@lists.febo.com> wrote:
>
> Hi everyone, wanting to pick the collective brains of the group
> regarding the use of dual frequency GPS antenna/receivers for NTP time
> servers. I work for an observatory that runs telescopes at various
> locations around the world and we had previously used Symmetricomm
> S250 and S300 NTP time servers to allow remote management and to
> provide NTP and IRIG-B signals but these are now affected by the Week
> Number Roll Over problem. With the lowering cost of dual frequency
> L1/L2 GPS receivers and antennas, I was thinking it would be nice to
> have a (likely separate) dual frequency receiver to allow estimation
> of the precipitable water vapor above the observatory. Timing
> precision needed for the NTP signals is the ~2-3ms expected over local
> Ethernet and ~20-50us for a 1PPS output for the future; commercial
> solutions rather than homebrew strongly preferred for the time server.
>
> So assuming that there aren't dual frequency time servers or a great
> deal of benefit of dual frequency receivers in a time server for this
> needed time precision:
> 1) Is putting a 2 way splitter in front on the time server to split
> the GPS signal for the time server and the experimental dual frequency
> receiver going to cause issues ? Are there recommended 2 way splitters
> that pass L1 and L2 well ?
> 2) Any recommendations for good quality but not insanely expensive
> L1/L2 antenna that will survive being on a pole on a remote high
> mountaintop for ~decade ?
>
> Thanks for any input,
> Tim
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
TL
Tim Lister
Wed, Oct 5, 2022 12:33 AM
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the server
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
If you do go with a dual freq GPS, you can do a very good job of working
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual freq
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
As always, tempered often by a lack of funds.
Tim
On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
>
> Hi
>
> The main issue with using the output of a GPS receiver directly is
> dropouts. They can be caused by a variety of things. When the GPS
> “goes away” you loose all timing information. Do these various things
> ( jamming, birds, lightning, …..) impact you? If they do, depending on
> just how the loss of timing impacts you, you do or don’t have a problem.
>
> Into an NTP server, the impact will still be there. How great an impact
> it is depends a *lot* on what the next level source going into the server
> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
> standards in them. That gives them a bit better performance than a
> typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
>
> If you *do* go with a dual freq GPS, you can do a very good job of working
> out the location of your antenna. With some effort that can improve the
> net timing accuracy. If post processing timing correction is ok in this
> case, that also is a lot easier / more accurate with a full set of dual freq
> GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
>
> So, when it works, you might be down into the < 10 ns range. When that
> bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
>
> Lots of tradeoffs.
As always, tempered often by a lack of funds.
Tim
>
> Bob
>
BK
Bob kb8tq
Wed, Oct 5, 2022 12:51 AM
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the server
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
If you do go with a dual freq GPS, you can do a very good job of working
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual freq
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
good enough to “not matter” for timing.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in the < 100 ns
range. If you do a good job on the single frequency stuff ( sawtooth correction ….)
the improvement is < 20 ns. There is a footnote down somewhere that mentions
some sort of “99.9% of the time” stuff. There are unusual solar events that can
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC. There also
is a chunk for antenna / cable delays and the like. This stuff impacts both approaches.
Normally that all should be < 100 ns. The delay part should be stable to < 20 ns in
a typical setup.
As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
Hi
> On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim@gmail.com> wrote:
>
> On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
>>
>> Hi
>>
>> The main issue with using the output of a GPS receiver directly is
>> dropouts. They can be caused by a variety of things. When the GPS
>> “goes away” you loose all timing information. Do these various things
>> ( jamming, birds, lightning, …..) impact you? If they do, depending on
>> just how the loss of timing impacts you, you do or don’t have a problem.
>>
>> Into an NTP server, the impact will still be there. How great an impact
>> it is depends a *lot* on what the next level source going into the server
>> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
>> standards in them. That gives them a bit better performance than a
>> typical DIY computer based NTP server.
>
> Yes they would definitely impact us. I neglected to mention that we
> have the rubidium oscillator option as backup in these units to
> provide holdover. Mostly to provide insurance/holdover for the case
> that weather takes out the antenna to give time to ship a replacement
> out from HQ in CA to whichever site was affected. Given that one of
> the time servers provides the IRIG-B signal for the 400 Hz control
> loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
> keen on a homebrew Raspberry Pi solution however much I like them for
> my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
>
>>
>> If you *do* go with a dual freq GPS, you can do a very good job of working
>> out the location of your antenna. With some effort that can improve the
>> net timing accuracy. If post processing timing correction is ok in this
>> case, that also is a lot easier / more accurate with a full set of dual freq
>> GPS data to correct against.
>
> A "real time" (latency ~<30 minutes) measure of the PWV would be
> helpful for scheduling/optimization of observations but there's also
> likely to be value in an improved value for use during later analysis
> at timescale >12 hours. Haven't done enough reading around of the
> literature on determining PWV from GPS to get a sense of where the
> error budget and improvements lie. I'm assuming something like a 48
> hour initial survey and having that post processed by e.g. the NRCan
> PPP service after the final GPS orbits are available would likely be a
> benefit but unclear how having a proper geodetic phase center vs a
> $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
> how much improvement in the water vapor determination comes from the
> increasingly precise (but increasingly delayed) GPS orbit products -
> it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
good enough to “not matter” for timing.
>>
>> So, when it works, you might be down into the < 10 ns range. When that
>> bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
>
> We're not an optical observatory so not in the pulsars & masers
> category. Driving demand on accuracy for us is normally very close,
> fast moving Near Earth Objects which can move at several hundred
> arcseconds/minute. If we don't want the timing uncertainty to degrade
> the position accuracy by more than the star catalog does, then we need
> timing precision in the ~1-10ms range. Determining diameters from
> occultations of stars by Kuiper Belt Objects, which have a transverse
> velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in the < 100 ns
range. If you do a good job on the single frequency stuff ( sawtooth correction ….)
the improvement is < 20 ns. There is a footnote down somewhere that mentions
some sort of “99.9% of the time” stuff. There are unusual solar events that can
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC. There also
is a chunk for antenna / cable delays and the like. This stuff impacts both approaches.
Normally that all should be < 100 ns. The delay part should be stable to < 20 ns in
a typical setup.
>>
>> Lots of tradeoffs.
>
> As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
>
> Tim
>
>>
>> Bob
>>
TS
Todd Smith
Wed, Oct 5, 2022 2:42 PM
As has been mentioned on the list recently, Jackson Labs builds a M12M
multi-GNSS receiver that is a drop-in replacement for the Furuno
receivers that are in the Syncservers that you are running right now.
If I am not mistaken, Galileo uses close enough frequency to GPS that you
can reuse the existing GPS antenna and receive both systems with a
multi-GNSS receiver like the Jackson Labs units.
Todd
On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
If you do go with a dual freq GPS, you can do a very good job of
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
good enough to “not matter” for timing.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in the
< 100 ns
range. If you do a good job on the single frequency stuff ( sawtooth
correction ….)
the improvement is < 20 ns. There is a footnote down somewhere that
mentions
some sort of “99.9% of the time” stuff. There are unusual solar events
that can
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC.
There also
is a chunk for antenna / cable delays and the like. This stuff impacts
both approaches.
Normally that all should be < 100 ns. The delay part should be stable to <
20 ns in
a typical setup.
As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
As has been mentioned on the list recently, Jackson Labs builds a M12M
multi-GNSS receiver that is a drop-in replacement for the Furuno
receivers that are in the Syncservers that you are running right now.
If I am not mistaken, Galileo uses close enough frequency to GPS that you
can reuse the existing GPS antenna and receive both systems with a
multi-GNSS receiver like the Jackson Labs units.
Todd
On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
time-nuts@lists.febo.com> wrote:
> Hi
>
> > On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim@gmail.com> wrote:
> >
> > On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
> >>
> >> Hi
> >>
> >> The main issue with using the output of a GPS receiver directly is
> >> dropouts. They can be caused by a variety of things. When the GPS
> >> “goes away” you loose all timing information. Do these various things
> >> ( jamming, birds, lightning, …..) impact you? If they do, depending on
> >> just how the loss of timing impacts you, you do or don’t have a problem.
> >>
> >> Into an NTP server, the impact will still be there. How great an impact
> >> it is depends a *lot* on what the next level source going into the
> server
> >> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
> >> standards in them. That gives them a bit better performance than a
> >> typical DIY computer based NTP server.
> >
> > Yes they would definitely impact us. I neglected to mention that we
> > have the rubidium oscillator option as backup in these units to
> > provide holdover. Mostly to provide insurance/holdover for the case
> > that weather takes out the antenna to give time to ship a replacement
> > out from HQ in CA to whichever site was affected. Given that one of
> > the time servers provides the IRIG-B signal for the 400 Hz control
> > loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
> > keen on a homebrew Raspberry Pi solution however much I like them for
> > my own time-nut home use...
>
> So indeed, having timing drop out is not a good thing ….
>
> >
> >>
> >> If you *do* go with a dual freq GPS, you can do a very good job of
> working
> >> out the location of your antenna. With some effort that can improve the
> >> net timing accuracy. If post processing timing correction is ok in this
> >> case, that also is a lot easier / more accurate with a full set of dual
> freq
> >> GPS data to correct against.
> >
> > A "real time" (latency ~<30 minutes) measure of the PWV would be
> > helpful for scheduling/optimization of observations but there's also
> > likely to be value in an improved value for use during later analysis
> > at timescale >12 hours. Haven't done enough reading around of the
> > literature on determining PWV from GPS to get a sense of where the
> > error budget and improvements lie. I'm assuming something like a 48
> > hour initial survey and having that post processed by e.g. the NRCan
> > PPP service after the final GPS orbits are available would likely be a
> > benefit but unclear how having a proper geodetic phase center vs a
> > $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
> > how much improvement in the water vapor determination comes from the
> > increasingly precise (but increasingly delayed) GPS orbit products -
> > it may be e.g. the Ultra Rapids are Good Enough.
>
> For about $100 ( delivered ) you can get a “pretty good” Chinese multi
> band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
> better than a hockey puck. With that and a week’s data into NRCan
> (it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
> good enough to “not matter” for timing.
>
> >>
> >> So, when it works, you might be down into the < 10 ns range. When that
> >> bird sits on that antenna …. microseconds …. takes a nap … milliseconds
> ….
> >
> > We're not an optical observatory so not in the pulsars & masers
> > category. Driving demand on accuracy for us is normally very close,
> > fast moving Near Earth Objects which can move at several hundred
> > arcseconds/minute. If we don't want the timing uncertainty to degrade
> > the position accuracy by more than the star catalog does, then we need
> > timing precision in the ~1-10ms range. Determining diameters from
> > occultations of stars by Kuiper Belt Objects, which have a transverse
> > velocity of ~15 km/s, leads to similar requirements.
>
> The advantages of all this stuff ( single band vs multi band ) are in the
> < 100 ns
> range. If you do a good job on the single frequency stuff ( sawtooth
> correction ….)
> the improvement is < 20 ns. There is a footnote down somewhere that
> mentions
> some sort of “99.9% of the time” stuff. There are unusual solar events
> that can
> push things well above the 20 ns range.
>
> Yes, there are other factors. There is another chunk for GPS <-> UTC.
> There also
> is a chunk for antenna / cable delays and the like. This stuff impacts
> both approaches.
> Normally that all should be < 100 ns. The delay part should be stable to <
> 20 ns in
> a typical setup.
>
> >>
> >> Lots of tradeoffs.
> >
> > As always, tempered often by a lack of funds.
>
> Somehow money always matters :)
>
> Bob
>
> >
> > Tim
> >
> >>
> >> Bob
> >>
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
TL
Tim Lister
Wed, Oct 5, 2022 3:34 PM
As has been mentioned on the list recently, Jackson Labs builds a M12M multi-GNSS receiver that is a drop-in replacement for the Furuno receivers that are in the Syncservers that you are running right now.
Any idea on pricing and whether it's just a plug-in replacement or
involves more serious surgery ? I've never had much luck in the past
getting replies from Jackson Labs.
If I am not mistaken, Galileo uses close enough frequency to GPS that you can reuse the existing GPS antenna and receive both systems with a multi-GNSS receiver like the Jackson Labs units.
Todd
On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:
Hi
On Oct 4, 2022, at 8:33 PM, Tim Lister listertim@gmail.com wrote:
On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq kb8tq@n1k.org wrote:
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a problem.
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the server
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
If you do go with a dual freq GPS, you can do a very good job of working
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of dual freq
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
good enough to “not matter” for timing.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in the < 100 ns
range. If you do a good job on the single frequency stuff ( sawtooth correction ….)
the improvement is < 20 ns. There is a footnote down somewhere that mentions
some sort of “99.9% of the time” stuff. There are unusual solar events that can
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC. There also
is a chunk for antenna / cable delays and the like. This stuff impacts both approaches.
Normally that all should be < 100 ns. The delay part should be stable to < 20 ns in
a typical setup.
Lots of tradeoffs.
As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
Tim
Bob
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
On Wed, Oct 5, 2022 at 7:43 AM Todd Smith <tssmith2002@gmail.com> wrote:
>
> As has been mentioned on the list recently, Jackson Labs builds a M12M multi-GNSS receiver that is a drop-in replacement for the Furuno receivers that are in the Syncservers that you are running right now.
Any idea on pricing and whether it's just a plug-in replacement or
involves more serious surgery ? I've never had much luck in the past
getting replies from Jackson Labs.
>
> If I am not mistaken, Galileo uses close enough frequency to GPS that you can reuse the existing GPS antenna and receive both systems with a multi-GNSS receiver like the Jackson Labs units.
>
> Todd
>
> On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <time-nuts@lists.febo.com> wrote:
>>
>> Hi
>>
>> > On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim@gmail.com> wrote:
>> >
>> > On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
>> >>
>> >> Hi
>> >>
>> >> The main issue with using the output of a GPS receiver directly is
>> >> dropouts. They can be caused by a variety of things. When the GPS
>> >> “goes away” you loose all timing information. Do these various things
>> >> ( jamming, birds, lightning, …..) impact you? If they do, depending on
>> >> just how the loss of timing impacts you, you do or don’t have a problem.
>> >>
>> >> Into an NTP server, the impact will still be there. How great an impact
>> >> it is depends a *lot* on what the next level source going into the server
>> >> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
>> >> standards in them. That gives them a bit better performance than a
>> >> typical DIY computer based NTP server.
>> >
>> > Yes they would definitely impact us. I neglected to mention that we
>> > have the rubidium oscillator option as backup in these units to
>> > provide holdover. Mostly to provide insurance/holdover for the case
>> > that weather takes out the antenna to give time to ship a replacement
>> > out from HQ in CA to whichever site was affected. Given that one of
>> > the time servers provides the IRIG-B signal for the 400 Hz control
>> > loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
>> > keen on a homebrew Raspberry Pi solution however much I like them for
>> > my own time-nut home use...
>>
>> So indeed, having timing drop out is not a good thing ….
>>
>> >
>> >>
>> >> If you *do* go with a dual freq GPS, you can do a very good job of working
>> >> out the location of your antenna. With some effort that can improve the
>> >> net timing accuracy. If post processing timing correction is ok in this
>> >> case, that also is a lot easier / more accurate with a full set of dual freq
>> >> GPS data to correct against.
>> >
>> > A "real time" (latency ~<30 minutes) measure of the PWV would be
>> > helpful for scheduling/optimization of observations but there's also
>> > likely to be value in an improved value for use during later analysis
>> > at timescale >12 hours. Haven't done enough reading around of the
>> > literature on determining PWV from GPS to get a sense of where the
>> > error budget and improvements lie. I'm assuming something like a 48
>> > hour initial survey and having that post processed by e.g. the NRCan
>> > PPP service after the final GPS orbits are available would likely be a
>> > benefit but unclear how having a proper geodetic phase center vs a
>> > $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
>> > how much improvement in the water vapor determination comes from the
>> > increasingly precise (but increasingly delayed) GPS orbit products -
>> > it may be e.g. the Ultra Rapids are Good Enough.
>>
>> For about $100 ( delivered ) you can get a “pretty good” Chinese multi
>> band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
>> better than a hockey puck. With that and a week’s data into NRCan
>> (it’s free ….. ) you can be pretty sure of your location to < 10 CM. That’s
>> good enough to “not matter” for timing.
>>
>> >>
>> >> So, when it works, you might be down into the < 10 ns range. When that
>> >> bird sits on that antenna …. microseconds …. takes a nap … milliseconds ….
>> >
>> > We're not an optical observatory so not in the pulsars & masers
>> > category. Driving demand on accuracy for us is normally very close,
>> > fast moving Near Earth Objects which can move at several hundred
>> > arcseconds/minute. If we don't want the timing uncertainty to degrade
>> > the position accuracy by more than the star catalog does, then we need
>> > timing precision in the ~1-10ms range. Determining diameters from
>> > occultations of stars by Kuiper Belt Objects, which have a transverse
>> > velocity of ~15 km/s, leads to similar requirements.
>>
>> The advantages of all this stuff ( single band vs multi band ) are in the < 100 ns
>> range. If you do a good job on the single frequency stuff ( sawtooth correction ….)
>> the improvement is < 20 ns. There is a footnote down somewhere that mentions
>> some sort of “99.9% of the time” stuff. There are unusual solar events that can
>> push things well above the 20 ns range.
>>
>> Yes, there are other factors. There is another chunk for GPS <-> UTC. There also
>> is a chunk for antenna / cable delays and the like. This stuff impacts both approaches.
>> Normally that all should be < 100 ns. The delay part should be stable to < 20 ns in
>> a typical setup.
>>
>> >>
>> >> Lots of tradeoffs.
>> >
>> > As always, tempered often by a lack of funds.
>>
>> Somehow money always matters :)
>>
>> Bob
>>
>> >
>> > Tim
>> >
>> >>
>> >> Bob
>> >>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
TS
Todd Smith
Wed, Oct 5, 2022 6:50 PM
Hello Tim,
I know many people have had problems in contacting Jackson Labs, but when I
called them I was able to get someone to call me back. they are in Las
Vegas so keep that in mind when you call them.
I paid $365 a unit plus a 2% CC fee and I installed two units just
purchased in 2 Syncserver S300 and it is a drop in replacement. I plugged
the new receiver into my laptop using USB and configured the settings that
I wanted. (GPS, SBAS, QZSS and Galileo, since I am using an
original Symmetricom GPS antenna)
After I configured the DIP switches so that SRAM settings were to be used
on power-up; I powered the receiver down and unbolted the S300. I took
screws out of the top and took the lid off. My Furuno receiver was secured
by 4 screws and standoffs. I unscrewed the screws and unplugged the GPS
antenna lead going to the BNC connector. I gently pulled up in the
receiver since it is plugged into the motherboard by a 10 pin Motorola
connector. I used the existing screws and standoffs from the orginial
Furuno receiver and plugged the new one in making sure that the pins
aligned on the motherboard. Plugged the GPS lead back in and powered up
the Syncserver. Pretty straight forward, nothing special I had to do.
Out of the box, the Jackson labs receiver is setup for GPS, SBAS, QZSS and
Glosnoss. I didn't think my antenna would work for Glosnoss so I chose
Galileo instead. You could also choose Beidou if you had the antenna for
it. Any 2 GNSS can be active at a time and the Syncserver doesn't know the
difference. It just sees more satellites at a time now. In my case, my
S300 didn't have room between the power supply and the receiver to leave
the USB cable plugged in all of the time so I needed to config it before I
installed it. In a different case, you could leave the USB cable plugged
in and extract timing or position information from it if you wished and
bypass or supplement your Syncserver.
The manual on Jackson Labs site was very useful to me as well as tech
support to answer some questions. I am not affiliated even though almost
all of my posts recently have been about the Jackson Labs receiver. I am
just a satisfied customer since my Furuno rolled over on Sept 18 2022 at
00:00 UTC
Todd
On Wed, Oct 5, 2022 at 11:34 AM Tim Lister listertim@gmail.com wrote:
As has been mentioned on the list recently, Jackson Labs builds a M12M
multi-GNSS receiver that is a drop-in replacement for the Furuno receivers
that are in the Syncservers that you are running right now.
Any idea on pricing and whether it's just a plug-in replacement or
involves more serious surgery ? I've never had much luck in the past
getting replies from Jackson Labs.
If I am not mistaken, Galileo uses close enough frequency to GPS that
you can reuse the existing GPS antenna and receive both systems with a
multi-GNSS receiver like the Jackson Labs units.
Todd
On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various
( jamming, birds, lightning, …..) impact you? If they do, depending
just how the loss of timing impacts you, you do or don’t have a
Into an NTP server, the impact will still be there. How great an
it is depends a lot on what the next level source going into the
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
If you do go with a dual freq GPS, you can do a very good job of
out the location of your antenna. With some effort that can improve
net timing accuracy. If post processing timing correction is ok in
case, that also is a lot easier / more accurate with a full set of
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM.
good enough to “not matter” for timing.
So, when it works, you might be down into the < 10 ns range. When
bird sits on that antenna …. microseconds …. takes a nap …
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in
range. If you do a good job on the single frequency stuff ( sawtooth
the improvement is < 20 ns. There is a footnote down somewhere that
some sort of “99.9% of the time” stuff. There are unusual solar events
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC.
is a chunk for antenna / cable delays and the like. This stuff impacts
Normally that all should be < 100 ns. The delay part should be stable
As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
Hello Tim,
I know many people have had problems in contacting Jackson Labs, but when I
called them I was able to get someone to call me back. they are in Las
Vegas so keep that in mind when you call them.
I paid $365 a unit plus a 2% CC fee and I installed two units just
purchased in 2 Syncserver S300 and it is a drop in replacement. I plugged
the new receiver into my laptop using USB and configured the settings that
I wanted. (GPS, SBAS, QZSS and Galileo, since I am using an
original Symmetricom GPS antenna)
After I configured the DIP switches so that SRAM settings were to be used
on power-up; I powered the receiver down and unbolted the S300. I took
screws out of the top and took the lid off. My Furuno receiver was secured
by 4 screws and standoffs. I unscrewed the screws and unplugged the GPS
antenna lead going to the BNC connector. I gently pulled up in the
receiver since it is plugged into the motherboard by a 10 pin Motorola
connector. I used the existing screws and standoffs from the orginial
Furuno receiver and plugged the new one in making sure that the pins
aligned on the motherboard. Plugged the GPS lead back in and powered up
the Syncserver. Pretty straight forward, nothing special I had to do.
Out of the box, the Jackson labs receiver is setup for GPS, SBAS, QZSS and
Glosnoss. I didn't think my antenna would work for Glosnoss so I chose
Galileo instead. You could also choose Beidou if you had the antenna for
it. Any 2 GNSS can be active at a time and the Syncserver doesn't know the
difference. It just sees more satellites at a time now. In my case, my
S300 didn't have room between the power supply and the receiver to leave
the USB cable plugged in all of the time so I needed to config it before I
installed it. In a different case, you could leave the USB cable plugged
in and extract timing or position information from it if you wished and
bypass or supplement your Syncserver.
The manual on Jackson Labs site was very useful to me as well as tech
support to answer some questions. I am not affiliated even though almost
all of my posts recently have been about the Jackson Labs receiver. I am
just a satisfied customer since my Furuno rolled over on Sept 18 2022 at
00:00 UTC
Todd
On Wed, Oct 5, 2022 at 11:34 AM Tim Lister <listertim@gmail.com> wrote:
> On Wed, Oct 5, 2022 at 7:43 AM Todd Smith <tssmith2002@gmail.com> wrote:
> >
> > As has been mentioned on the list recently, Jackson Labs builds a M12M
> multi-GNSS receiver that is a drop-in replacement for the Furuno receivers
> that are in the Syncservers that you are running right now.
>
> Any idea on pricing and whether it's just a plug-in replacement or
> involves more serious surgery ? I've never had much luck in the past
> getting replies from Jackson Labs.
>
> >
> > If I am not mistaken, Galileo uses close enough frequency to GPS that
> you can reuse the existing GPS antenna and receive both systems with a
> multi-GNSS receiver like the Jackson Labs units.
> >
> > Todd
> >
> > On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
> time-nuts@lists.febo.com> wrote:
> >>
> >> Hi
> >>
> >> > On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim@gmail.com> wrote:
> >> >
> >> > On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
> >> >>
> >> >> Hi
> >> >>
> >> >> The main issue with using the output of a GPS receiver directly is
> >> >> dropouts. They can be caused by a variety of things. When the GPS
> >> >> “goes away” you loose all timing information. Do these various
> things
> >> >> ( jamming, birds, lightning, …..) impact you? If they do, depending
> on
> >> >> just how the loss of timing impacts you, you do or don’t have a
> problem.
> >> >>
> >> >> Into an NTP server, the impact will still be there. How great an
> impact
> >> >> it is depends a *lot* on what the next level source going into the
> server
> >> >> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
> >> >> standards in them. That gives them a bit better performance than a
> >> >> typical DIY computer based NTP server.
> >> >
> >> > Yes they would definitely impact us. I neglected to mention that we
> >> > have the rubidium oscillator option as backup in these units to
> >> > provide holdover. Mostly to provide insurance/holdover for the case
> >> > that weather takes out the antenna to give time to ship a replacement
> >> > out from HQ in CA to whichever site was affected. Given that one of
> >> > the time servers provides the IRIG-B signal for the 400 Hz control
> >> > loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
> >> > keen on a homebrew Raspberry Pi solution however much I like them for
> >> > my own time-nut home use...
> >>
> >> So indeed, having timing drop out is not a good thing ….
> >>
> >> >
> >> >>
> >> >> If you *do* go with a dual freq GPS, you can do a very good job of
> working
> >> >> out the location of your antenna. With some effort that can improve
> the
> >> >> net timing accuracy. If post processing timing correction is ok in
> this
> >> >> case, that also is a lot easier / more accurate with a full set of
> dual freq
> >> >> GPS data to correct against.
> >> >
> >> > A "real time" (latency ~<30 minutes) measure of the PWV would be
> >> > helpful for scheduling/optimization of observations but there's also
> >> > likely to be value in an improved value for use during later analysis
> >> > at timescale >12 hours. Haven't done enough reading around of the
> >> > literature on determining PWV from GPS to get a sense of where the
> >> > error budget and improvements lie. I'm assuming something like a 48
> >> > hour initial survey and having that post processed by e.g. the NRCan
> >> > PPP service after the final GPS orbits are available would likely be a
> >> > benefit but unclear how having a proper geodetic phase center vs a
> >> > $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
> >> > how much improvement in the water vapor determination comes from the
> >> > increasingly precise (but increasingly delayed) GPS orbit products -
> >> > it may be e.g. the Ultra Rapids are Good Enough.
> >>
> >> For about $100 ( delivered ) you can get a “pretty good” Chinese multi
> >> band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
> >> better than a hockey puck. With that and a week’s data into NRCan
> >> (it’s free ….. ) you can be pretty sure of your location to < 10 CM.
> That’s
> >> good enough to “not matter” for timing.
> >>
> >> >>
> >> >> So, when it works, you might be down into the < 10 ns range. When
> that
> >> >> bird sits on that antenna …. microseconds …. takes a nap …
> milliseconds ….
> >> >
> >> > We're not an optical observatory so not in the pulsars & masers
> >> > category. Driving demand on accuracy for us is normally very close,
> >> > fast moving Near Earth Objects which can move at several hundred
> >> > arcseconds/minute. If we don't want the timing uncertainty to degrade
> >> > the position accuracy by more than the star catalog does, then we need
> >> > timing precision in the ~1-10ms range. Determining diameters from
> >> > occultations of stars by Kuiper Belt Objects, which have a transverse
> >> > velocity of ~15 km/s, leads to similar requirements.
> >>
> >> The advantages of all this stuff ( single band vs multi band ) are in
> the < 100 ns
> >> range. If you do a good job on the single frequency stuff ( sawtooth
> correction ….)
> >> the improvement is < 20 ns. There is a footnote down somewhere that
> mentions
> >> some sort of “99.9% of the time” stuff. There are unusual solar events
> that can
> >> push things well above the 20 ns range.
> >>
> >> Yes, there are other factors. There is another chunk for GPS <-> UTC.
> There also
> >> is a chunk for antenna / cable delays and the like. This stuff impacts
> both approaches.
> >> Normally that all should be < 100 ns. The delay part should be stable
> to < 20 ns in
> >> a typical setup.
> >>
> >> >>
> >> >> Lots of tradeoffs.
> >> >
> >> > As always, tempered often by a lack of funds.
> >>
> >> Somehow money always matters :)
> >>
> >> Bob
> >>
> >> >
> >> > Tim
> >> >
> >> >>
> >> >> Bob
> >> >>
> >> _______________________________________________
> >> time-nuts mailing list -- time-nuts@lists.febo.com
> >> To unsubscribe send an email to time-nuts-leave@lists.febo.com
>
TS
Todd Smith
Sat, Jan 14, 2023 5:19 PM
I am looking for replacement power supplies for a S300. They use a Powdec
HDT125-43 power supply that is hard to find. Powdec is out of business and
this power supply is a triple output unit +5v, +15v, -15v.
Anyone have a dead or decommissioned unit or spare power supplies that they
would be willing to part with for a nominal sum?
Thanks for a great list! I learn something new most days.
Todd Smith
On Wed, Oct 5, 2022, 10:42 Todd Smith tssmith2002@gmail.com wrote:
As has been mentioned on the list recently, Jackson Labs builds a M12M
multi-GNSS receiver that is a drop-in replacement for the Furuno
receivers that are in the Syncservers that you are running right now.
If I am not mistaken, Galileo uses close enough frequency to GPS that you
can reuse the existing GPS antenna and receive both systems with a
multi-GNSS receiver like the Jackson Labs units.
Todd
On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
time-nuts@lists.febo.com> wrote:
Hi
The main issue with using the output of a GPS receiver directly is
dropouts. They can be caused by a variety of things. When the GPS
“goes away” you loose all timing information. Do these various things
( jamming, birds, lightning, …..) impact you? If they do, depending on
just how the loss of timing impacts you, you do or don’t have a
Into an NTP server, the impact will still be there. How great an impact
it is depends a lot on what the next level source going into the
is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
standards in them. That gives them a bit better performance than a
typical DIY computer based NTP server.
Yes they would definitely impact us. I neglected to mention that we
have the rubidium oscillator option as backup in these units to
provide holdover. Mostly to provide insurance/holdover for the case
that weather takes out the antenna to give time to ship a replacement
out from HQ in CA to whichever site was affected. Given that one of
the time servers provides the IRIG-B signal for the 400 Hz control
loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
keen on a homebrew Raspberry Pi solution however much I like them for
my own time-nut home use...
So indeed, having timing drop out is not a good thing ….
If you do go with a dual freq GPS, you can do a very good job of
out the location of your antenna. With some effort that can improve the
net timing accuracy. If post processing timing correction is ok in this
case, that also is a lot easier / more accurate with a full set of
GPS data to correct against.
A "real time" (latency ~<30 minutes) measure of the PWV would be
helpful for scheduling/optimization of observations but there's also
likely to be value in an improved value for use during later analysis
at timescale >12 hours. Haven't done enough reading around of the
literature on determining PWV from GPS to get a sense of where the
error budget and improvements lie. I'm assuming something like a 48
hour initial survey and having that post processed by e.g. the NRCan
PPP service after the final GPS orbits are available would likely be a
benefit but unclear how having a proper geodetic phase center vs a
$200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
how much improvement in the water vapor determination comes from the
increasingly precise (but increasingly delayed) GPS orbit products -
it may be e.g. the Ultra Rapids are Good Enough.
For about $100 ( delivered ) you can get a “pretty good” Chinese multi
band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
better than a hockey puck. With that and a week’s data into NRCan
(it’s free ….. ) you can be pretty sure of your location to < 10 CM.
That’s
good enough to “not matter” for timing.
So, when it works, you might be down into the < 10 ns range. When that
bird sits on that antenna …. microseconds …. takes a nap …
We're not an optical observatory so not in the pulsars & masers
category. Driving demand on accuracy for us is normally very close,
fast moving Near Earth Objects which can move at several hundred
arcseconds/minute. If we don't want the timing uncertainty to degrade
the position accuracy by more than the star catalog does, then we need
timing precision in the ~1-10ms range. Determining diameters from
occultations of stars by Kuiper Belt Objects, which have a transverse
velocity of ~15 km/s, leads to similar requirements.
The advantages of all this stuff ( single band vs multi band ) are in the
< 100 ns
range. If you do a good job on the single frequency stuff ( sawtooth
correction ….)
the improvement is < 20 ns. There is a footnote down somewhere that
mentions
some sort of “99.9% of the time” stuff. There are unusual solar events
that can
push things well above the 20 ns range.
Yes, there are other factors. There is another chunk for GPS <-> UTC.
There also
is a chunk for antenna / cable delays and the like. This stuff impacts
both approaches.
Normally that all should be < 100 ns. The delay part should be stable to
< 20 ns in
a typical setup.
As always, tempered often by a lack of funds.
Somehow money always matters :)
Bob
I am looking for replacement power supplies for a S300. They use a Powdec
HDT125-43 power supply that is hard to find. Powdec is out of business and
this power supply is a triple output unit +5v, +15v, -15v.
Anyone have a dead or decommissioned unit or spare power supplies that they
would be willing to part with for a nominal sum?
Thanks for a great list! I learn something new most days.
Todd Smith
On Wed, Oct 5, 2022, 10:42 Todd Smith <tssmith2002@gmail.com> wrote:
> As has been mentioned on the list recently, Jackson Labs builds a M12M
> multi-GNSS receiver that is a drop-in replacement for the Furuno
> receivers that are in the Syncservers that you are running right now.
>
> If I am not mistaken, Galileo uses close enough frequency to GPS that you
> can reuse the existing GPS antenna and receive both systems with a
> multi-GNSS receiver like the Jackson Labs units.
>
> Todd
>
> On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
> time-nuts@lists.febo.com> wrote:
>
>> Hi
>>
>> > On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim@gmail.com> wrote:
>> >
>> > On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq@n1k.org> wrote:
>> >>
>> >> Hi
>> >>
>> >> The main issue with using the output of a GPS receiver directly is
>> >> dropouts. They can be caused by a variety of things. When the GPS
>> >> “goes away” you loose all timing information. Do these various things
>> >> ( jamming, birds, lightning, …..) impact you? If they do, depending on
>> >> just how the loss of timing impacts you, you do or don’t have a
>> problem.
>> >>
>> >> Into an NTP server, the impact will still be there. How great an impact
>> >> it is depends a *lot* on what the next level source going into the
>> server
>> >> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
>> >> standards in them. That gives them a bit better performance than a
>> >> typical DIY computer based NTP server.
>> >
>> > Yes they would definitely impact us. I neglected to mention that we
>> > have the rubidium oscillator option as backup in these units to
>> > provide holdover. Mostly to provide insurance/holdover for the case
>> > that weather takes out the antenna to give time to ship a replacement
>> > out from HQ in CA to whichever site was affected. Given that one of
>> > the time servers provides the IRIG-B signal for the 400 Hz control
>> > loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
>> > keen on a homebrew Raspberry Pi solution however much I like them for
>> > my own time-nut home use...
>>
>> So indeed, having timing drop out is not a good thing ….
>>
>> >
>> >>
>> >> If you *do* go with a dual freq GPS, you can do a very good job of
>> working
>> >> out the location of your antenna. With some effort that can improve the
>> >> net timing accuracy. If post processing timing correction is ok in this
>> >> case, that also is a lot easier / more accurate with a full set of
>> dual freq
>> >> GPS data to correct against.
>> >
>> > A "real time" (latency ~<30 minutes) measure of the PWV would be
>> > helpful for scheduling/optimization of observations but there's also
>> > likely to be value in an improved value for use during later analysis
>> > at timescale >12 hours. Haven't done enough reading around of the
>> > literature on determining PWV from GPS to get a sense of where the
>> > error budget and improvements lie. I'm assuming something like a 48
>> > hour initial survey and having that post processed by e.g. the NRCan
>> > PPP service after the final GPS orbits are available would likely be a
>> > benefit but unclear how having a proper geodetic phase center vs a
>> > $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
>> > how much improvement in the water vapor determination comes from the
>> > increasingly precise (but increasingly delayed) GPS orbit products -
>> > it may be e.g. the Ultra Rapids are Good Enough.
>>
>> For about $100 ( delivered ) you can get a “pretty good” Chinese multi
>> band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
>> better than a hockey puck. With that and a week’s data into NRCan
>> (it’s free ….. ) you can be pretty sure of your location to < 10 CM.
>> That’s
>> good enough to “not matter” for timing.
>>
>> >>
>> >> So, when it works, you might be down into the < 10 ns range. When that
>> >> bird sits on that antenna …. microseconds …. takes a nap …
>> milliseconds ….
>> >
>> > We're not an optical observatory so not in the pulsars & masers
>> > category. Driving demand on accuracy for us is normally very close,
>> > fast moving Near Earth Objects which can move at several hundred
>> > arcseconds/minute. If we don't want the timing uncertainty to degrade
>> > the position accuracy by more than the star catalog does, then we need
>> > timing precision in the ~1-10ms range. Determining diameters from
>> > occultations of stars by Kuiper Belt Objects, which have a transverse
>> > velocity of ~15 km/s, leads to similar requirements.
>>
>> The advantages of all this stuff ( single band vs multi band ) are in the
>> < 100 ns
>> range. If you do a good job on the single frequency stuff ( sawtooth
>> correction ….)
>> the improvement is < 20 ns. There is a footnote down somewhere that
>> mentions
>> some sort of “99.9% of the time” stuff. There are unusual solar events
>> that can
>> push things well above the 20 ns range.
>>
>> Yes, there are other factors. There is another chunk for GPS <-> UTC.
>> There also
>> is a chunk for antenna / cable delays and the like. This stuff impacts
>> both approaches.
>> Normally that all should be < 100 ns. The delay part should be stable to
>> < 20 ns in
>> a typical setup.
>>
>> >>
>> >> Lots of tradeoffs.
>> >
>> > As always, tempered often by a lack of funds.
>>
>> Somehow money always matters :)
>>
>> Bob
>>
>> >
>> > Tim
>> >
>> >>
>> >> Bob
>> >>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
>
>
GH
Glen Hoag
Sat, Jan 14, 2023 10:03 PM
On Jan 14, 2023, at 15:33, Todd Smith via time-nuts time-nuts@lists.febo.com wrote:
I am looking for replacement power supplies for a S300. They use a Powdec
HDT125-43 power supply that is hard to find. Powdec is out of business and
this power supply is a triple output unit +5v, +15v, -15v.
Anyone have a dead or decommissioned unit or spare power supplies that they
would be willing to part with for a nominal sum?
Thanks for a great list! I learn something new most days.
Todd Smith
I’m not aware of any replacements, but oftentimes replacing all the electrolytic capacitors with modern 105C units will bring a SMPS back to life.
Sent from my iPhone
> On Jan 14, 2023, at 15:33, Todd Smith via time-nuts <time-nuts@lists.febo.com> wrote:
>
> I am looking for replacement power supplies for a S300. They use a Powdec
> HDT125-43 power supply that is hard to find. Powdec is out of business and
> this power supply is a triple output unit +5v, +15v, -15v.
>
> Anyone have a dead or decommissioned unit or spare power supplies that they
> would be willing to part with for a nominal sum?
>
> Thanks for a great list! I learn something new most days.
>
> Todd Smith
I’m not aware of any replacements, but oftentimes replacing all the electrolytic capacitors with modern 105C units will bring a SMPS back to life.
