Bicentennial GOES satellite clock
Hi
It’s back in the FCS archives. I don’t think it’s one of the ones you can hit without going through a
paywall. It was a fun paper to attend. The chatter in the room was “interesting” to say the least.
Bob
On Aug 31, 2018, at 1:07 PM, Brooke Clarke brooke@pacific.net wrote:
Hi Bob:
Do you have and info on that article that would allow me to read it?
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
https://www.end2partygovernment.com/2012Issues.html
axioms:
- The extent to which you can fix or improve something will be limited by how well you understand how it works.
- Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
Hi
The original “we cracked GPS” paper back in the 1980’s (that unlimitedly lead to the end of SA)
used a medium sized dish ( think of the good old C-band antennas) to pick out a single sat.
Bob
On Aug 30, 2018, at 9:54 PM, Brooke Clarke brooke@pacific.net wrote:
Hi Gregory:
I wonder if anyone has tried using a small parabolic dish, like used for Free To Air satellite TV and aimed it at a GPS satellite track or at a WAAS geostationary satellite using a feed antenna with reverse polarization from a normal GPS antenna?
http://www.prc68.com/I/FTA.shtml
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
https://www.end2partygovernment.com/2012Issues.html
axioms:
- The extent to which you can fix or improve something will be limited by how well you understand how it works.
- Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
On Thu, Aug 30, 2018 at 9:43 PM Brooke Clarke brooke@pacific.net wrote:
I would disagree in that ease of jamming/spoofing is strongly related to wavelength. That's because antenna efficiency
goes down as the size of the antenna gets smaller than 1/4 wave.
So, it's easy to make a GPS jammer (1,100 to 1,600MHz) since a 1/4 wavelength is a few inches, something that you can
hold in your hand.
However, the short wavelengths of GPS make beam forming a reasonable
countermeasure against jamming.
By having a small array of GPS antennas a receiver can digitally form
beams that both aim directly at the relevant satellites (so even
reducing intersatellite interference) while also steering a deep null
in the direction of the jammer. If the jammer is powerful enough to
overload the front-end then this won't help, but against a
non-targeted area denying jammer it should be fairly effective.
There are many papers on GNSS beamforming. ( e.g.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5134596/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5134483/ )
This kind of anti-jamming solution should even be pretty inexpensive
-- really no more than the cost of N receivers. Except that it is
specialized technology and thus very expensive. :)
Seeing some open source software implementing beam-forming was one of
the things I hoped to see result from the open hardware multi-band
GNSS receivers like the GNSS firehose project (
http://pmonta.com/blog/2017/05/05/gnss-firehose-update/ ) since once
you're going through the trouble of running three coherent receivers
for three bands, stacking three more of them and locking them to the
same clock doesn't seem like a big engineering challenge... and the
rest is just DSP work.
Even absent fancy beam forming, for GNSS timing with a surveyed
position except at high latitudes it should be possible to use a
relatively high gain antenna pointed straight up and by doing so blind
yourself to terrestrial jammers at a cost of fewer SVs being
available. But I've never tried it.
In an urban area I noticed my own GPSDOs losing signal multiple times
per week. Monitoring with an SDR showed what appeared to be jammers.
As others have noted intermittent jamming is pretty benign to a GPSDO.
Spoofing, OTOH, can trivially mess up the timing. It's my view that
if you need timing for a security critical purpose there isn't really
any GNSS based solution commercially available to the general public
right now, the best bet is a local atomic reference with a GPSDO used
to monitor and initially set it.
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Hi Azelio:
Thanks for the link.
It's interesting that their setup (a Ku band satellite TV antenna and a standard GPS timing antenna) worked as well as
it did with reversed polarity. Does anyone know of a source of reverse polarity GPS antennas and a GPS timing receiver
that also processes WAAS signals?
--
Have Fun,
Brooke Clarke
https://www.PRC68.com
https://www.end2partygovernment.com/2012Issues.html
axioms:
- The extent to which you can fix or improve something will be limited by how well you understand how it works.
- Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
Maybe this one is equivalent?
http://freqelec.com/gps_gnss/waas_for_telecom_2-07.pdf
On Fri, Aug 31, 2018 at 4:55 PM Attila Kinali attila@kinali.ch wrote:
On Thu, 30 Aug 2018 18:54:17 -0700
Brooke Clarke brooke@pacific.net wrote:
I wonder if anyone has tried using a small parabolic dish, like used for Free To Air satellite TV and aimed it at a GPS
satellite track or at a WAAS geostationary satellite using a feed antenna with reverse polarization from a normal GPS
antenna?
I have somewhere a paper (which i cannot find currently, sorry) that
used a dish trained at one of the EGNOS satellites and used it as the
only source for timing. IIRC the results were promising, but not
spectacular. The problem being that all the ionospheric and tropospheric
effects limited the performance, which also could not be averaged
over several satellites. Hence most people today focus on whole
constelation systems and try to get the best out of that, even under
multipath and jamming.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neal Stephenson
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On Fri, Aug 31, 2018 at 5:16 PM jimlux jimlux@earthlink.net wrote:
AJ is a slightly different problem than straight up beamforming
You need N+1 receivers to suppress N point source jammers - it's more of
an adaptive canceller than a beamformer.
One nice property of AJ though is that the nulls it forms can be very
deep, so the result is much more suppression than you might have
expected from looking at the lobe gains from beamforming. This is for
the same reason that normal radio direction finding uses e.g. the null
in a loop antenna.
It's also an argument as to why few antennas are sufficient for
blocking jammers at a single location.
In general, you're probably not going to design to "notch" a sinusoid -
sure that might be a common jammer, but the sinewave generated by the
jammer might be very noisy and unstable in frequency - sort of the
opposite of the sinusoids desired by list members :) - the spurious
oscillation of the TV antenna amplifier was in this bucket.
Hm. My belief that a sinusoid notch was interesting in part because of
how badly a loud one trashes a bit-depth reduced signal compared to
e.g. pulse interference with an equivalent amount of energy.
With infinite bit depth I wouldn't expect a narrowband jammer to be
particularly bothersome after despreading (at least not more than any
other jamming signal that isn't correlated with the spreading code).
[As an aside, the sinusoidal estimation paper I linked can also model
higher order parameters like amplitude and frequency modulation,
including 2nd order and higher modulation, assuming you have enough
SNR for those terms to be anything but noise.]
Then you get into sophisticated approaches which are more like spoofing
- transmit a PN modulated signal that replicates the desired signal,
then pull it away and turn off, forcing the receiver to be in
"acquisition" mode all the time.
Indeed, and with SDR so inexpensive, making a jammer that produces a
spoof GPS signal is something a bored teenager can do.
Can you build a receiver which is immune to all of these and sell it for
$10? Probably not. Can you do it for $100-1000, almost certainly.
A robust timing receiver with a parts cost of $1000 many would buy
now, but I think the issue is that the first unit costs $10m ... it's
only the nth thousandth one built that costs $1000. :P
holdover GPSDO is a tiny, tiny part of the cost of a cell site -
Installation of the concrete pad for the tower probably costs more.
Indeed, but people are now using GPS based timing for security
critical applications where skewing someones clock lets you steal
millions in an electronic bank heist. We don't actually see any of
these attacks right now in part because it's still much easier to
attack by social engineering humans or leaving malware on USB sticks
outside an office... but also because people who are aware of these
risks put in a local atomic clock instead of getting their timing from
a GPSDO, but many aren't aware of the risks.
On 8/31/18 10:31 AM, Brooke Clarke wrote:
Hi Azelio:
Thanks for the link.
It's interesting that their setup (a Ku band satellite TV antenna and a
standard GPS timing antenna) worked as well as it did with reversed
polarity. Does anyone know of a source of reverse polarity GPS antennas
and a GPS timing receiver that also processes WAAS signals?
you could wind your own helix - it's pretty non critical.
or just use linear pol, and take the 3dB hit. I'll bet the EGNOS + small
dish has enough gain to make up for it. (but the gain of a dish that is
a few lambda across isn't huge)
On 08/30/2018 11:20 PM, Brooke Clarke wrote:
Hi Bob:
I would disagree in that ease of jamming/spoofing is strongly related to
wavelength. That's because antenna efficiency goes down as the size of
the antenna gets smaller than 1/4 wave.
So, it's easy to make a GPS jammer (1,100 to 1,600MHz) since a 1/4
wavelength is a few inches, something that you can hold in your hand.
It's harder to make a WWV jammer (.5, 5, 10, 15, 20 MHz) since a 1/4
wavelength in in the range of 500 to 12 feet, something that can be
mounted on a vehicle for the higher frequencies.
But it's extremely hard to make a jammer for WWVB (60 kHz) where a
1/4wavelength is over 4,000 feet. This means an antenna that can be
vehicle mounted will be very inefficient. Note this also means that it's
extremely hard to make a Loran-C jammer. Note that the WWVB and LORAN-C
transmitters run very high power and the antennas are massive.
Locally you can transmit with a much smaller antenna. It's been shown
and works.
Sweden used to have a network of 212 m towers to jam and spoof
Loran-C/Chayka. It was a top secret network.
This also means that if someone makes a WWVB simulator for their house
the signal at the next door neighbor's house is probably going to be too
small to effect their clocks.
Magnetic loop works, non-resonant suffice. Magnetic lopp is used for
hearing aid, and it doesn't take much. Enough for the house. Not getting
you very far though.
PS. Some decades ago I maintained a beacon transmitter "LAH" on 175 kHz
where the rules for unlicensed operation limited the input power to 1
Watt and total antenna length to 50 feet. Under these conditions the
effective radiated power might be 2 milliwatts, orders of magnitude less
if a portable system.
http://www.auroralchorus.com/pli/1750meter_antennas.pdf
The 137 kHz band for radio amateurs is limited, but with radiated power,
and getting up to that power is a great success and considering the band
and that one use CW it should be fun.
Cheers,
Magnus
Hi,
On 08/31/2018 12:18 AM, Poul-Henning Kamp wrote:
In message 96e995c4-5ca2-af02-9738-0a6d87a9f813@pacific.net, Brooke Clarke writes:
But it's extremely hard to make a jammer for WWVB (60 kHz) [...]
You can do it city-scale with a 18-wheeler sized loop-antenna
and a good size diesel-generator.
However pedestrians will very likely note metalic items vibrating
as they pass the "mystery white truck".
Sweden were much more serious about it:
http://www.antus.org/RT02.html
Tl;drs:
They erected 9 200m tall Loran-C class antennas each driven by
a Loran-C transmitter with an advanced degree which could jam
Loran-C or Chayka.
They even mounted decoy parabolas on the towers them to hide their
true purpose.
The fact that all the transmitters were on the east coast does drop
a hint that swedens much touted neutrality had a bit of a slant.
The "On" switch of the network where in the air defenece bunker. It was
only marked with "På" (Swedish for On) with no further markings. It was
designed for when the soviet bombers comes, at least they should loose
their Chayka guidance.
I knew one of the folks that where boss over the system, was to his
funeral recently. He also worked hard to get the classified material and
make a public report out of it. Time to refresh your swedish, as I doubt
any translations exist in public.
Cheers,
Magnus
On 08/31/2018 03:36 PM, Bob kb8tq wrote:
Hi
“Backbone timing” gets done by boxes buried deep in systems. Those systems take years
to design. The boxes that go in them similarly take years to get onto the market. Once designed
deployment is far from instantaneous. Operators are always pressed by cost constraints. Adding
anything beyond the minimums … not going to happen.
The result is that there are no systems out there that use WWVB or WWV other than wrist watches
and wall clock like devices. Utilities (cell phones, internet, finance ) run with something else. Converting
them to a secondary “something” is a many years sort of thing, even if it is technically feasible.
You can pull a bunch of spare GPS sat’s out of storage and get them in orbit way quicker than you can
rebuild every cell tower in the country. In fact, newer designs run their timing in a way that a GPS failure
is not that big a deal. How long it’ll take before that sort of design is common in the US…. years and years …
If you are going to come up with a time source at the ~ 10 ns level, that’s not going to happen from WWVB
or WWV. They never were good enough to get to that level and it’s not on the transmit end. You would need
a very different system. It’s been a long time since any of these services (internet, finance, cell ) were in the
millisecond or even the microsecond range. The modern stuff in all theses areas is < 100 ns.
The actual requirements is usually on the 1-10 us level, but they are
happy when they have the extra precision.
How long would it take to change all this? Well first some random Senior Member of the IEEE would
have to start writing papers about the various issues. Various organizations in various countries would
need to hold meeting after meeting after meeting talking things over. Somebody eventually would have
to come up with funds to actually try a few things. Maybe they work in the real world / maybe they don’t
work.
Once you prove you have a system that can do “good enough", you would need laws / regulations passed to
make the “new thing” part of the required designs. You also need funding bills to deploy the “source” end
of things and time to get that up and running. Once it’s running, you then give manufacturers some amount of time
to get it in the field ….. and extensions when that doesn’t happen. Twenty years? Thirty years? Maybe longer?
This stuff does not go very fast.
It's been done for 10+ years now. Some 15+ countries have nation wide
networks that makes them GPS independent for some applications.
It has been a fun system to design and deploy.
Getting more precision isn't all that hard, it just takes more effort in
the details and hence money and time. If people need 100 ns or 10 ns
system time, it can be done.
Best bet on what the “new thing” would be? Something like IEEE-1588 over fiber. It cuts out a bunch of this and
that in terms of experiments and testing the basic system. We know most of how to do it already. It’s just a matter
of a billions of dollars in tax money to get the gaps filled in and then a few tens of billions in tax money to get
the backbone gear in place. Once that’s done you ramp up to the really expensive part of the deal ….Is it paid
for by your tax return in April or by a higher price on every cell call / transaction you make? … who knows … it’s
a tax that you are paying either way.
IEEE 1588 isn't working out at all for WAN, it's stuck in LAN
environment, which is the dirty little secret of the industry. There is
trials for dedicated wavelengths with using 1588 or it's extension White
Rabbit that works great, but in any form of production environment it's
a mess.
Network based precision timing takes a number of hurdles to handle. I've
done my fair bit of them.
Cheers,
Magnus
Hi
On Sep 1, 2018, at 3:06 AM, Magnus Danielson magnus@rubidium.dyndns.org wrote:
On 08/31/2018 03:36 PM, Bob kb8tq wrote:
Hi
“Backbone timing” gets done by boxes buried deep in systems. Those systems take years
to design. The boxes that go in them similarly take years to get onto the market. Once designed
deployment is far from instantaneous. Operators are always pressed by cost constraints. Adding
anything beyond the minimums … not going to happen.
The result is that there are no systems out there that use WWVB or WWV other than wrist watches
and wall clock like devices. Utilities (cell phones, internet, finance ) run with something else. Converting
them to a secondary “something” is a many years sort of thing, even if it is technically feasible.
You can pull a bunch of spare GPS sat’s out of storage and get them in orbit way quicker than you can
rebuild every cell tower in the country. In fact, newer designs run their timing in a way that a GPS failure
is not that big a deal. How long it’ll take before that sort of design is common in the US…. years and years …
If you are going to come up with a time source at the ~ 10 ns level, that’s not going to happen from WWVB
or WWV. They never were good enough to get to that level and it’s not on the transmit end. You would need
a very different system. It’s been a long time since any of these services (internet, finance, cell ) were in the
millisecond or even the microsecond range. The modern stuff in all theses areas is < 100 ns.
The actual requirements is usually on the 1-10 us level, but they are
happy when they have the extra precision.
Well, they are and they aren’t. The newer systems (which rapidly become the only system) are at the one microsecond
level after being in holder for many hours ( days?). The assumption is that only one tower (or chunk) goes into holdover
at a time and the rest are still at least 10X better than that. Cut them all loose an the numbers would have to be tighter.
In order to get them all at the 100 ns level, you need a source that is around 5 to 10X better than that. The timing source
is not the only source of error and you need to “train” your holdover clock with something that is mighty good. The
holdover spec often applies after a very short period of training (a day to several days). Indeed, if you put a Cs standard
in every cell tower and every internet node you probably could back off a bit on the 10X. With quartz or Rb, you need
the accuracy in training.
Bob
How long would it take to change all this? Well first some random Senior Member of the IEEE would
have to start writing papers about the various issues. Various organizations in various countries would
need to hold meeting after meeting after meeting talking things over. Somebody eventually would have
to come up with funds to actually try a few things. Maybe they work in the real world / maybe they don’t
work.
Once you prove you have a system that can do “good enough", you would need laws / regulations passed to
make the “new thing” part of the required designs. You also need funding bills to deploy the “source” end
of things and time to get that up and running. Once it’s running, you then give manufacturers some amount of time
to get it in the field ….. and extensions when that doesn’t happen. Twenty years? Thirty years? Maybe longer?
This stuff does not go very fast.
It's been done for 10+ years now. Some 15+ countries have nation wide
networks that makes them GPS independent for some applications.
It has been a fun system to design and deploy.
Getting more precision isn't all that hard, it just takes more effort in
the details and hence money and time. If people need 100 ns or 10 ns
system time, it can be done.
Best bet on what the “new thing” would be? Something like IEEE-1588 over fiber. It cuts out a bunch of this and
that in terms of experiments and testing the basic system. We know most of how to do it already. It’s just a matter
of a billions of dollars in tax money to get the gaps filled in and then a few tens of billions in tax money to get
the backbone gear in place. Once that’s done you ramp up to the really expensive part of the deal ….Is it paid
for by your tax return in April or by a higher price on every cell call / transaction you make? … who knows … it’s
a tax that you are paying either way.
IEEE 1588 isn't working out at all for WAN, it's stuck in LAN
environment, which is the dirty little secret of the industry. There is
trials for dedicated wavelengths with using 1588 or it's extension White
Rabbit that works great, but in any form of production environment it's
a mess.
Network based precision timing takes a number of hurdles to handle. I've
done my fair bit of them.
Cheers,
Magnus
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