GPS Signals and Western Headings

C150J

C150J

Well-Known Member
Hi all:

There seems to be a myth about better GPS reception coming from Westbound headings over North America. For example, I have heard of people specifically putting portable GPS receivers on the right window when heading southbound, claiming that it somehow results in better reception.

Unless I'm missing something, I'm having a hard time believing this (looking at ephemeris data, there seems to be equal coverage regardless of heading) . Can someone enlighten me?

Thanks!
 
In would think with portable devices the GPS antenna is fine in any location. Its the XM portion that is more location sensitive. A friend tried XM radio in his machine with the portable antenna an could get signal on south bound headings only. So music HNS to JNU but nothing on the way back.
 
Since the GPS satellites are constantly moving, this makes no sense. WAAS satellites, however, are geosynchronous, so they are in a fixed position. There seem to be more positioned to the south, rather than the west.
 
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mojo6911 said:
Since the GPS satellites are constantly moving, this makes no sense. WAAS satellites, however, are geosynchronous, so they are in a fixed position. There seem to be more positioned to the south, rather than the west.
Click to expand...
Ya, they're moving, but given the sheer number of them, there should be no lapse in coverage at all. The N/S thing on XM is interesting, but that's another constellation that I know little about. To put something in geosynchronous costs a lot more due to the altitude.
Simply put, I have never as much have had a WAAS outage let along any gps signal degradation in an airplane anywhere in the continental US.
 
I've heard that for XM reception you always put the antenna on the "gulf side" (ie the south side) of the dash. In airplanes that I've flown with fixed exterior xm antennas, I never really had a problem with reception from what I remember.


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C150J said:
Hi all:

There seems to be a myth about better GPS reception coming from Westbound headings over North America. For example, I have heard of people specifically putting portable GPS receivers on the right window when heading southbound, claiming that it somehow results in better reception.

Unless I'm missing something, I'm having a hard time believing this (looking at ephemeris data, there seems to be equal coverage regardless of heading) . Can someone enlighten me?

Thanks!
Click to expand...
The only time that I've ever had a GPS receiver up and quit ("NO RAIM/NO NAV-DR") was on a northerly heading. Right inside the final approach fix, IMC, in mountainous terrain, at night. Yeah, it's a good time.

When we added GPS to the Twin Bonanza, I briefly read up on GPS installations. An IFR-certificated (read: non handheld) installation is supposed to have sufficient visibility to the satellites in all normal flight attitudes, and is to be mounted so that it has good visibility of the horizon. I would make an educated guess that the presence of aircraft structure around most handheld GPS, XM, etc. antennae (many are in the cabin) is the reason for their relatively lousy performance.
 
You need good visibility to the south (from the northern hemisphere) to see the geostationary satellites such as WAAS and XM. Usually won't have any issues except low on approach with mountains to the south of you especially at high latitudes. Or by placing handheld receivers on the north side of the interior of the airplane.
 
I had no bad experiences with the GPS's I was using unless it was a military or satellite operation in effect.
 
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