Dom writes:

… on my recent transcontinental odyssey, pretty much over the GAFA, (if you don’t know what the GAFA is, I’ll explain it off LML), both my Garmin 295 and AvMap EK IV lost satellite signals intermittently every few seconds, while the KLN89B happily continued to receive all available satellites. This went on for some time.

 

Dom,

I have a Garmin 295 that’s about as reliable and trustworthy as any piece of electronic equipment I own. Having said that, one of the radios in my Cherokee will definitely disrupt the signal on certain frequencies. It is so predictable on 119.3 (a primary approach control freq for our flying area) that I initially concluded that the GPS signal was being jammed in a specific geographic area—took me months to make the association to a change of ATC frequencies. The interesting thing is that radio #1 will jam the GPS if tuned to 119.3 every time, but radio #2 does not affect it. My suspicion is that there are some IF frequencies in the Narco radio that “walk on” the GPS signal—or perhaps internal circuitry in the GPS itself? Having “discovered” this, I have now taken to switching radios/frequencies any time I lose the GPS signal, and have thereby compiled a short list of frequencies, when tuned into the Narco, that interfere. I have discovered only one frequency on the King radio that interferes, and it’s a different freq…go figure. In any case, you might give this some consideration.

Dom, Bob,

 

If one installs a panel mount GPS, there is a required interference test of about 10-15 specific radio frequencies.  I believe the fix is for certain filters to be added to the gps antenna connection.  The attached pdf  is two pages from the 430W install manual.  It is useful to read it and consider possible interference to your handheld although the interfering frequencies may be different.