Re: [time-nuts] Tuning a Trimble Thunderbolt
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking
at the DAC voltage and temperature reporting during holdover and
attempting to reverse engineer the prediction algorithm by
correlating those with the long-term DAC voltage -- good luck).
Also, are there any published details about how the training works?
Not as far as the time-nuts community knows, no.
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if
they have been powered down. Because of the lack of precise retrace
of quartz crystals, I don't think you'd want old (pre-power-down)
data, anyway. Some crystals will even come up drifting in the
opposite direction after being powered down, and they all take some
time (days, at least) to settle down after any disturbance (including
power interruptions, however brief).
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m
introduces a +/- 33nS error in the raw data (as much as 33nS closer
to some satellites and 33nS farther from others). Add in the
uncertainty due to noise, and you get easily hundreds on nS of error
in the computed solution.
Unfortunately, you are unlikely to do any better than this with the
antenna location you described. Time to buy a house, with no tall
trees nearby. (You may already have heard that time-nuttiness can be
expensive.... ;-)
Best regards,
Charles
On 4/20/15 7:25 PM, Charles Steinmetz wrote:
Unfortunately, you are unlikely to do any better than this with the
antenna location you described. Time to buy a house, with no tall trees
nearby. (You may already have heard that time-nuttiness can be
expensive.... ;-)
Actually, what you want is an isolated mountain top of solid granite
connected to a big pluton below, with a nice drilled anchor. Your
laboratory/lair can be in a cave below the mountain top.
Being on top of a tall mountain also reduces the effect of atmospheric
effects, but will increase the solid earth tides (and, of course, you
are closer to the moon and sun).
I wonder if being on top of a dormant volcano (e.g. Mt. Waialeale on
Kauai) would be stable. An active volcano (Mauna Kea/Mauna Loa) is
going to be moving around a lot. Tahiti, perhaps? Nice pleasant
weather. Mt. Roriama in Venezuela appears to be well above the
surroundings, but is quite flat on top, so you'd need a structure to get
your choke ring antenna up high enough. Close to the equator too.
As the previous poster pointed out, serious time-nuttery can get expensive.
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
csteinmetz@yandex.com wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
On Tue, Apr 21, 2015 at 1:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
You can let the GPS receiver do a self-survey but you can also enter
the location that you determined by other means. I've not done this
on a Thunderbolt but have for my Motorola receivers. Just by chance
I needed to get my property surveyed and had a crew out and they
marked the property with brass markers positioned to a fraction of an
inch. (I hope) From this I can figure out the antenna location to
likely about one foot or maybe better if I am really carful.
One thing to watch out for is that there are different "systems" of
measuring latitude and longitude these make different assumptions
about the shape of the Earth and where its center is located and so
on. You need to be sure everyone is using WGS84. If not it is easy
to be "off" by a couple hundred meters
You can use Google Earth if you don't have a survey but check it for
accuracy. Have Google check the location of a government benchmark
that is nearest your house and see if Google gives you the recorded
location.
It's good to find the antenna location using other means so you can
verify the self-survey.. I did this and found it is all OK within
some margin of error. But then I have a very good antenna location.
I think with a poor antenna location you'd want to verify the
self-survey
--
Chris Albertson
Redondo Beach, California
A week is somewhat optimistic since the thunderbolt consumes around 1.68 kilowatt hours of energy. With a 12V battery a capacity of around 84 ampere hours (for an efficiency of 100%) which is somewhat larger than that provided for most UPS particularly those sold for use with personal computers. .Whilst the UPS may use a higher battery voltage the energy requirements are similar as will be the physical size and weight of the battery/battteries.
Bruce
On Wednesday, 22 April 2015 6:33 PM, Chris Albertson <albertson.chris@gmail.com> wrote:
On Tue, Apr 21, 2015 at 1:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
You can let the GPS receiver do a self-survey but you can also enter
the location that you determined by other means. I've not done this
on a Thunderbolt but have for my Motorola receivers. Just by chance
I needed to get my property surveyed and had a crew out and they
marked the property with brass markers positioned to a fraction of an
inch. (I hope) From this I can figure out the antenna location to
likely about one foot or maybe better if I am really carful.
One thing to watch out for is that there are different "systems" of
measuring latitude and longitude these make different assumptions
about the shape of the Earth and where its center is located and so
on. You need to be sure everyone is using WGS84. If not it is easy
to be "off" by a couple hundred meters
You can use Google Earth if you don't have a survey but check it for
accuracy. Have Google check the location of a government benchmark
that is nearest your house and see if Google gives you the recorded
location.
It's good to find the antenna location using other means so you can
verify the self-survey.. I did this and found it is all OK within
some margin of error. But then I have a very good antenna location.
I think with a poor antenna location you'd want to verify the
self-survey
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
Backing up a bit to “getting a TBolt running”.
- instal Lady Heather and get it connected to the TBolt
- does it fire up and find any sats?
- are the power supplies holding regulation?
- nail down the antenna in the best fixed location you can find
- run the auto-calibration feature in LH
- run a 48 hour survey with LH and write the location to ee memory
- Then check the EFC voltage, it should be fairly close to 0V, and not over 2.5
If you are > 2.5, that’s probably a broken unit. - Now start watching the EFC voltage for a few days and see that it’s leveling
out and not spiking. Again spikes = something broke.
Until that’s all done, I would not dig to deep into the workings of the gizmo. It
needs to be set up first.
Bob
On Apr 21, 2015, at 4:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
csteinmetz@yandex.com wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp kb8tq@n1k.org wrote:
Hi
Backing up a bit to “getting a TBolt running”.
- instal Lady Heather and get it connected to the TBolt
- does it fire up and find any sats?
Yes. It had been working consistently for several days prior to my
first message.
- are the power supplies holding regulation?
Yes.
- nail down the antenna in the best fixed location you can find
Done.
- run the auto-calibration feature in LH
Done. This changed the gain from -5.0Hz/V to -3.132Hz/V and changed
the initial voltage to 0.347V. I switched the time constant and
damping values back to their defaults of 100 seconds and 1.200,
respectively.
- run a 48 hour survey with LH and write the location to ee memory
Done. The location matches the averaged location surveyed from my
Motorola Oncore UT+ (the antenna for which was about 10cm away from
that for the Tbolt, some no-name mushroom-type antenna) and a handheld
Garmin eTrex 20 (with GPS+GLONASS+WAAS) within a few meters. It also
matches with Google Maps.
In the attached screenshot you can clearly see the field of view from
the antenna's current location over the last ~20 hours.
Interestingly, the Oncore antenna (a cheap patch antenna from eBay)
seems to be causing some intermittent issues with the Tbolt: if the
antennas are too close there appears to be some sort of interference
emitted by the Oncore antenna that makes it difficult for the Tbolt to
lock onto the GPS signal and the Tbolt goes into holdover. Oddly, this
is not consistent: the Tbolt and Oncore had coexisted for a few days
with no problems but today some of the problems started up again.
The same issue occured if the Oncore antenna was too close to my
Garmin GPS 18x LVC. I have since moved the Oncore antenna further away
(it's now about 50cm) and signal reception for the Tbolt is much
better. Weird, but distance seems to resolve the issue, so not really
a problem anymore.
- Then check the EFC voltage, it should be fairly close to 0V, and not over 2.5
If you are > 2.5, that’s probably a broken unit.
Doesn't seem to be a problem.
- Now start watching the EFC voltage for a few days and see that it’s leveling
out and not spiking. Again spikes = something broke.
See the attached screenshot. There's a few small EFC voltage spikes
when the unit enters or leaves holdover, but otherwise it seems
reasonably smooth in my (admittedly untrained) view.
Until that’s all done, I would not dig to deep into the workings of the gizmo. It
needs to be set up first.
Other than the intermittent issues with the Oncore antenna, everything
seems to be working reasonably well -- there's no obvious failures
that I can spot.
Cheers!
-Pete
Bob
On Apr 21, 2015, at 4:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
csteinmetz@yandex.com wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Pete Stephenson
Hi
Looking at that screen shot, something is very wrong with your GPS reception. Your GPS
is 10X worse than it should be.
On Apr 22, 2015, at 9:37 AM, Pete Stephenson pete@heypete.com wrote:
On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp kb8tq@n1k.org wrote:
Hi
Backing up a bit to “getting a TBolt running”.
- instal Lady Heather and get it connected to the TBolt
- does it fire up and find any sats?
Yes. It had been working consistently for several days prior to my
first message.
- are the power supplies holding regulation?
Yes.
- nail down the antenna in the best fixed location you can find
Done.
- run the auto-calibration feature in LH
Done. This changed the gain from -5.0Hz/V to -3.132Hz/V and changed
the initial voltage to 0.347V. I switched the time constant and
damping values back to their defaults of 100 seconds and 1.200,
respectively.
- run a 48 hour survey with LH and write the location to ee memory
Done. The location matches the averaged location surveyed from my
Motorola Oncore UT+ (the antenna for which was about 10cm away from
that for the Tbolt, some no-name mushroom-type antenna) and a handheld
Garmin eTrex 20 (with GPS+GLONASS+WAAS) within a few meters. It also
matches with Google Maps.
In the attached screenshot you can clearly see the field of view from
the antenna's current location over the last ~20 hours.
Interestingly, the Oncore antenna (a cheap patch antenna from eBay)
seems to be causing some intermittent issues with the Tbolt: if the
antennas are too close there appears to be some sort of interference
emitted by the Oncore antenna that makes it difficult for the Tbolt to
lock onto the GPS signal and the Tbolt goes into holdover. Oddly, this
is not consistent: the Tbolt and Oncore had coexisted for a few days
with no problems but today some of the problems started up again.
I would bet that the amp on the “Oncore” antenna is oscillating. It may do it
intermittently. The frequency may swing back and forth through the GPS band. It
may be the source of your GPS problem.
Bob
The same issue occured if the Oncore antenna was too close to my
Garmin GPS 18x LVC. I have since moved the Oncore antenna further away
(it's now about 50cm) and signal reception for the Tbolt is much
better. Weird, but distance seems to resolve the issue, so not really
a problem anymore.
- Then check the EFC voltage, it should be fairly close to 0V, and not over 2.5
If you are > 2.5, that’s probably a broken unit.
Doesn't seem to be a problem.
- Now start watching the EFC voltage for a few days and see that it’s leveling
out and not spiking. Again spikes = something broke.
See the attached screenshot. There's a few small EFC voltage spikes
when the unit enters or leaves holdover, but otherwise it seems
reasonably smooth in my (admittedly untrained) view.
Until that’s all done, I would not dig to deep into the workings of the gizmo. It
needs to be set up first.
Other than the intermittent issues with the Oncore antenna, everything
seems to be working reasonably well -- there's no obvious failures
that I can spot.
Cheers!
-Pete
Bob
On Apr 21, 2015, at 4:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
csteinmetz@yandex.com wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Pete Stephenson
<tbolt2.gif>_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Thu, Apr 23, 2015 at 12:33 AM, Bob Camp kb8tq@n1k.org wrote:
Hi
Looking at that screen shot, something is very wrong with your GPS reception. Your GPS
is 10X worse than it should be.
You're right. The interference from the nearby Oncore UT+ seems to
have been the problem. Since I moved the antennas further apart the
signal strength for satellites in view of the Tbolt is 35-45 dBc and
it can routinely view 6-7 satellites simultaneously -- this is
essentially the same performance as when the Oncore is powered off and
the antenna removed, so I'm happy.
After moving the antennas further apart and doing a standard
2000-point site survey the 100-200ns phase offset spikes that occurred
when satellites were added/removed from the solution dropped to
5-10ns. The oscillator offset also decreased. I'm now doing a longer
precision survey to hopefully smooth those out more and get a better
average position over a few satellite orbits.
I would bet that the amp on the “Oncore” antenna is oscillating. It may do it
intermittently. The frequency may swing back and forth through the GPS band. It
may be the source of your GPS problem.
Interesting. I have a second identical Oncore UT+ and antenna and will
do some more tests to see if one of them is just being noisy, if it's
a fault of the Oncore module itself, or the antenna.
Many thanks to everyone on the list for the insight and assistance.
Cheers!
-Pete
--
Pete Stephenson
Bob from the screenshot what is it that shows the GPS reception as very wrong. just curious.
-=Bryan=-
From: kb8tq@n1k.org
Date: Wed, 22 Apr 2015 18:33:09 -0400
To: time-nuts@febo.com
Subject: Re: [time-nuts] Tuning a Trimble Thunderbolt
Hi
Looking at that screen shot, something is very wrong with your GPS reception. Your GPS
is 10X worse than it should be.
On Apr 22, 2015, at 9:37 AM, Pete Stephenson pete@heypete.com wrote:
On Wed, Apr 22, 2015 at 1:47 PM, Bob Camp kb8tq@n1k.org wrote:
Hi
Backing up a bit to “getting a TBolt running”.
- instal Lady Heather and get it connected to the TBolt
- does it fire up and find any sats?
Yes. It had been working consistently for several days prior to my
first message.
- are the power supplies holding regulation?
Yes.
- nail down the antenna in the best fixed location you can find
Done.
- run the auto-calibration feature in LH
Done. This changed the gain from -5.0Hz/V to -3.132Hz/V and changed
the initial voltage to 0.347V. I switched the time constant and
damping values back to their defaults of 100 seconds and 1.200,
respectively.
- run a 48 hour survey with LH and write the location to ee memory
Done. The location matches the averaged location surveyed from my
Motorola Oncore UT+ (the antenna for which was about 10cm away from
that for the Tbolt, some no-name mushroom-type antenna) and a handheld
Garmin eTrex 20 (with GPS+GLONASS+WAAS) within a few meters. It also
matches with Google Maps.
In the attached screenshot you can clearly see the field of view from
the antenna's current location over the last ~20 hours.
Interestingly, the Oncore antenna (a cheap patch antenna from eBay)
seems to be causing some intermittent issues with the Tbolt: if the
antennas are too close there appears to be some sort of interference
emitted by the Oncore antenna that makes it difficult for the Tbolt to
lock onto the GPS signal and the Tbolt goes into holdover. Oddly, this
is not consistent: the Tbolt and Oncore had coexisted for a few days
with no problems but today some of the problems started up again.
I would bet that the amp on the “Oncore” antenna is oscillating. It may do it
intermittently. The frequency may swing back and forth through the GPS band. It
may be the source of your GPS problem.
Bob
The same issue occured if the Oncore antenna was too close to my
Garmin GPS 18x LVC. I have since moved the Oncore antenna further away
(it's now about 50cm) and signal reception for the Tbolt is much
better. Weird, but distance seems to resolve the issue, so not really
a problem anymore.
- Then check the EFC voltage, it should be fairly close to 0V, and not over 2.5
If you are > 2.5, that’s probably a broken unit.
Doesn't seem to be a problem.
- Now start watching the EFC voltage for a few days and see that it’s leveling
out and not spiking. Again spikes = something broke.
See the attached screenshot. There's a few small EFC voltage spikes
when the unit enters or leaves holdover, but otherwise it seems
reasonably smooth in my (admittedly untrained) view.
Until that’s all done, I would not dig to deep into the workings of the gizmo. It
needs to be set up first.
Other than the intermittent issues with the Oncore antenna, everything
seems to be working reasonably well -- there's no obvious failures
that I can spot.
Cheers!
-Pete
Bob
On Apr 21, 2015, at 4:30 AM, Pete Stephenson pete@heypete.com wrote:
On Tue, Apr 21, 2015 at 4:25 AM, Charles Steinmetz
csteinmetz@yandex.com wrote:
Pete wrote:
On a related note, is it possible to extract any data regarding the
training from the unit?
Not as far as the time-nuts community knows, no (other than looking at the
DAC voltage and temperature reporting during holdover and attempting to
reverse engineer the prediction algorithm by correlating those with the
long-term DAC voltage -- good luck).
Finishing my PhD is enough work already. I don't think I'll try
reverse-engineering the prediction algorithm quite yet. Perhaps later
in my Copious Free Time(tm)?
Are the training parameters saved periodically to non-volatile memory,
or are they purely stored in RAM and so will be lost if powered down?
If the latter, does the RAM have any provisions for backup power
I doubt it -- mine always act as if they are training from zero if they have
been powered down. Because of the lack of precise retrace of quartz
crystals, I don't think you'd want old (pre-power-down) data, anyway. Some
crystals will even come up drifting in the opposite direction after being
powered down, and they all take some time (days, at least) to settle down
after any disturbance (including power interruptions, however brief).
Ok. It'd be nice if there was some way to keep the crystal going
through power interruptions, even if the oven itself cooled off. I
suspect Trimble (correctly) assumed that the vast majority of these
units were to be installed in cell sites with reliable power so that
wouldn't be an issue.
Alas, the location for the antenna is suboptimal: in the best location
available to me (an outdoor balcony) I have a clear view of the
southern sky from 150-300 degrees (az) and from horizon to zenith with
only a few low-elevation obstructions. However, this is only
accessible in warm months
* * *
The surveyed position is within about 10 meters of the actual location
according to Google Maps and local building information.
That's a problem. Every meter is approximately 3.3nS, so 10m introduces a
+/- 33nS error in the raw data (as much as 33nS closer to some satellites
and 33nS farther from others). Add in the uncertainty due to noise, and you
get easily hundreds on nS of error in the computed solution.
Indeed. I'm running a 48-hour survey with Lady Heather now to see if
that can improve things a bit more.
Unfortunately, you are unlikely to do any better than this with the antenna
location you described. Time to buy a house, with no tall trees nearby.
(You may already have heard that time-nuttiness can be expensive.... ;-)
I won't be looking for a house for at least a few years, but when I do
the skyview is definitely one of the criteria, as is the friendliness
of the community to radio masts.
Cheers!
-Pete
--
Pete Stephenson
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