"Position Unknowm"

[rv7guy2]

Hi There. Anyone experience what I am experiencing and can suggest a fix?
  I began flying my newly installed dual screen Dynon Skyview a week ago. I installed and configured the GPS 2020 unit in serial port 5 as directed. In the 5 flights I have logged to date, I get a "position unknown" flag on the MAP page for 1 to 2 seconds and then things return to normal. This has happened at least 2X on every flight and in each case the extended distance and time lubber line of the airplane symbol searches for direction. After 1-2 seconds things return to normal, the track line remains as before,as does the entered flight plan. So, why is the GPS 2020 momentarily losing position? A friend of mine who also has a dual screen set up with a GPS 2020 has NOT had the same issue, neither has another friend with a single screen GPS 2020 installed.
  Any ideas what's happening and can suggest a fix?
Thanks
Dave

 

[Dynon]

That's definitely not expected. Where is the SV-GPS-2020 mounted? Is it near any other electronics or antennas?

 

[rv7guy2]

The GPS 2020 is mounted on the glare shield under the windscreen..as far forward as I can get it..very close to where the windscreen intersects the top forward skin. it is relatively close to the  canopy bow support tube ( I have a slider on my RV-7). it's the same location where I had mounted  the antennae module for the Garmin GPS I was using before purchashing the SkyView system. Never has a similar "problem" with the Garmin .
  I can turn the 2020 unit 90 degrees and move it a little away from the support tube, not much though as the connecting wires  won't allow too much movement. Anywhere else on the airframe would mean lengthening the wires.
Dave

 

[swatson999]

Download the data logs and look through them...what does GPS Fix Quality and # of satellites say?

 

[Dynon]

Lengthening the wires on the SV-GPS-2020 wouldn't be an issue. It's a self-contained receiver/antenna combo and nothing would be degraded by lengthening them. Having the SV-GPS-2020 externally mounted is probably the best advice we could give for troubleshooting this. But you might get in touch with our support team at 425-402-0433 or support at dynonavionics dot com for some further thoughts.

 

[swatson999]

I'd also check for possible interference at the known L1 harmonic frequencies in the VHF comm range...

 

[jakej]

Like Steve indicates, I'd be checking to see if the 'dropout' happens just after transmitting on the Com.

 

[swatson999]

Yeah, it smells like RF interference to me, and possibly destructive harmonic interference which is *known* to occur at certain COM frequencies (and should be tested for during initial installation/checkout).

 

[jakej]

agree. interference checks are supposed to be carried out with avionics in IFR installations too however I'm not sure that many people do that

 

[jakej]

agree. interference checks are supposed to be carried out with avionics in IFR installations (according to the install manuals) too however I'm not sure that many people do that

 

[Garrett]

It is also recommended and owner/PIC should to run the FAA's ADS-B performance report at least monthly to verify system performance/compliance. For those of us who have ADS-B out.

 

[swatson999]

agree. interference checks are supposed to be carried out with avionics in IFR installations (according to the install manuals) too however I'm not sure that many people do that 

Here's one who did

 

[Raymo]

Data Point:

I have the GPS-2020 installed in about the same place in my RV-7A and it has worked perfectly for the past 18 months. I also installed the older GPS as a backup. Both antennas are fed to/by each SV 1000T screen.

My VHF antenna is under the co-pilot seat. Transponder is fwd of the right-side spar and ADS-B in is fwd of the left side spar.