Hi Brian!

Hmmm... should I finish the thread before commenting...

The scenario has been discussed on the list before. There are publications from Zyfer (fei) on Waas timing with a fixed dish antenna. There is also a Fenton(Novatel) patent.

--  

    Björn

The ultimate goal is to try and reduce the number of times when full sky view GPS antennas are victims of GPS band interference.  This is only a half-baked idea of mine (in my day-job) but wanted Time Nuts feedback to see if it has any merit at all. BTW, the system has Rb for hold-over when there are problems but the frequent system error alarms indicating hold-over events is what I/we would like to reduce. New SNMP traps could mask off the events, but being an RF guy.....I was thinking about a HW solution. :- )

-Brian, WA1ZMS/4
iPhone

On Jan 7, 2014, at 11:05 PM, Magnus Danielson magnus@rubidium.dyndns.org wrote:

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Guys-

Thanks for the inputs and the mention of FEI and related patents. I thought the idea was not new but did not remember the details.

As for some answers:
As far as I have seen first-hand, the jamming is short in nature and events that I saw were from trucks on highways trying to defeat any tracking systems in the trucks.  An FCC enforcement issue here in the US resulted in one such user being made an example of by heavy fines since his truck was near a major airport where the FAA was trying to test GPS landing aids.

In my case, SW masking of hold-over alarms may be a shorter fix without any HW fixes. But that said, I wanted to be sure I understood the situation/mitigation at least well enough to talk about it with some info as back-up.

As for Hal's drop-out of GPS in the SFO area, that was a location that I had to address with a customer 18 months ago who was having chronic GPS drop-outs that I traced to GPS jamming and documented. Could be the same or not.

This latest issue is on the East Coast.

Again, there is a wealth of great knowledge here in Time Nuts and I'm glad to be able to call on help!

-Brian, WA1ZMS/4
iPhone

On Jan 8, 2014, at 11:57 AM, Björn bg@lysator.liu.se wrote:

On Wed, Jan 8, 2014 at 12:02 PM, Brian, WA1ZMS wa1zms@att.net wrote:

As far as I have seen first-hand, the jamming is short in nature and events

I have experienced loss of GPS while using it as my primary nav-aid while
flying. Twice it occurred over the ocean while out of sight of land. I
suspected at that time that it was a general outage (it took down my
panel-mount GPS as well as my hand-held back-up), but now suspect that it
was close-in jamming.

I remember the general availability of Russian-made GPS jammers about 15
years ago. I didn't realize that the use of GPS jamming was prevalent.

--
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian@lloyd.com
+1.916.877.5067

Brian, WA1ZMS  wrote:

If you can mask short-duration alarms while still finding out about persistent ones, then yes, that's probably the most pragmatic solution. What's your holdover tolerance?

Following from that, suppose a jammer parks nearby and doesn't leave in a timely fashion. How long does it take for the FCC to swoop in (do they swoop? in my mind they do) and find the source? Is that within your permissible holdover window?

But back to your original WAAS question, it sounds like it's time to haul out the spare hardware and do some experiments! Even with the normal antenna, you should be able to assess the validity of the configuration. Will the receiver even let you specify just those few birds? It's almost a question of whether they bothered to code an error message for such a stunt...

(This next part may deserve its own thread. Please edit the subject-line if replying to just this bit.)

You might look into a CDMA-derived time source, long term. By working one stratum away from GPS, you'll be listening to a plurality of pilots, each of which is GPS-derived, and which are geographically diverse. A single GPS jammer shouldn't knock out more than one tower at a time, and even if the tower's local holdover OCXO isn't stellar and it begins to drift, your CDMA-derived receiver is continually comparing and assessing the different signals to discard the outliers.

Ideally, it's like having a bunch of diverse receive sites feeding back to you on a jam-resistant (very strong) channel. Pessimistically, you've got no visibility into the internal operation of those sites, and the only way to infer their status is by comparing them against each other (or a local GPS receiver, if you're not presently jammed yourself).

As far as I can tell, the CDMA receivers are less explored than GPS, so you'd be largely taking the manufacturer's word on a lot of things.

73 de NJ8Z

We have a Rb for hold-over that is good for 72hrs per our needs. So we are fine in that regard.

That said, the vendor of the GPS box is a bit to fast and our equipment is also in some regards a bit too fast to report a string of alarms when both the main and hot-standby units go into hold-over.
We can manage that with the vendor and our own equipment alarm reporting.

The "jamming" events are fast and unpredictable given the ever-growing use of GPS jammers that anyone can find via a fly-by-night web page. The FCC is also staff limited to deal with fast and dynamic events. I am not sure that anybody can find a mobile and time dynamic jammer. One thing I did learn is that you will never find a truck with an active jammer at a sea port or transfer station. They WANT to be logged as being at those locations. Yet once on the road, jammer is often "on" so they can get cargo to destination ahead of schedule and get a pay bonus for doing a prompt job. Keep in mind that L1 jammers are easy to obtain that make as much as 3W of RF power on the L1 freq. Please don't ask me how I know.

On this forum I cannot go into details due to nature of my day-job and our customers, but that said my original question has been answered by the FEI  papers that claim that a WAAS directional antenna has some advantage.  As usual for me, I tried to re-invent the wheel.

CDMA or cellular timing is not a viable option if our systems need to be more robust than a cell phone network.

Sorry, I cannot go into our customer base.

-Brian, WA1ZMS/4
iPhone

On Jan 8, 2014, at 5:18 PM, Nathaniel Bezanson myself@telcodata.us wrote:

Nathaniel wrote:

One of my clients had exactly that problem with radar detectors in
parked cars interfering with its satellite earth stations.  In that
case, the answer was about three years.

Best regards,

Charles

On Wed, Jan 08, 2014 at 08:09:04PM -0500, Charles Steinmetz wrote:

Did the FCC actually DO anything about these things ?

I imagine there are some type acceptance issues that could

be invoked here...

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

On 1/8/14 9:06 PM, David I. Emery wrote:

It depends on what's being interfered with.  Park your jammer on the
approach to a big airport on a foggy night and jam the glide slope and
localizer, and the DF van will be out there in minutes.

Run a bootleg FM station that doesn't interfere with any one, and you'll
get a NOUO in the mail eventually.

In general, jamming or interfering with public safety gets the attention
and more rapid enforcement actions.

Yes, it eventually initiated a rulemaking and amended Part 15 of the
rules to reduce (but not entirely eliminate) the problem.  It never
did anything about the installed base of noncompliant devices.

Best regards,

Charles