GPS 2020 problems?

[rfazio1951]

My friend and I were having difficulties with his dual HDX panel and the 2020 antenna. He was getting POS source 1 fail. Today we got Dynon tech support to give us a call while at the airport and Jeff of tech support, and I, went through the setup. All settings were correct. Then I asked if being under the RV tip up canopy on the glare shield mattered. He said probably not, that was fine. I asked if having a Stratus sitting next to it mattered? He said it should be two feet away. Hmm, so while on the satellite page with about 12 satellites acquired in green, I turned on the stratus. Well, they all went yellow and to half strength. We couldn’t believe it. I moved the stratus away from the 2020 and they all came back on full green. I think we figured out the problem.

So, if any of you have a 2020 mounted on the glare shield, make sure you don’t put a stratus near it!

 

[DBRV10]

This applies to ALL GPS antennas. Minimum 2 feet from each other.

 

[ned]

This applies to ALL GPS antennas. Minimum 2 feet from each other.

My 2020 and 250 antennas sit 2" apart with no issues.

 

[GalinHdz]

FWIW, these are NOT just antennas but basically "remote GPS receivers". They combine the antenna with a pre-amplifier, sometimes an IF converter and a digital data circuit. A lot more happening in those GPS "pucks" than just a wire antenna.

 

[airguy]

This applies to ALL GPS antennas. Minimum 2 feet from each other.

Not necessarily.

I have the Dynon GPS2020, Garmin 430W, and G5 antennas all nustled up snugly together under my cowling. No issues at all, 5 years and 720+ hours now.

To your point though - SOME antennas do not play nicely with others - but a blanket statement is not a true one. Testing your individual configuration is the only way to be sure. I used to own a pickup that would blank out any GPS device in the vehicle everytime you turned on the AM radio. FM or XM, everything worked fine, but there was some IF frequency on the AM board that completely squashed the GPS frequencies.

 

[Raymo]

Garmin specifies 6" separation between GPS antennas in the G3X manual. I've seen many that are like @airguy with no issues.

Page 23-5 rev AM.

To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be mounted
no closer than 6 inches (edge to edge) from other antennas, including passive antennas such as
another GPS antenna or XM antenna.

 

[dlloyd]

If the manufacturer says not to mount antennas under the canopy or cowling and not closer than 2' or 8" you should heed their instructions. It might and probably will work just fine but you're on your own. Don't call and complain. Another problem that a lot of people ignore is the potential for other equipment to interfere with each other. My KX-165 would knock out several satellites' reception every time the mic was keyed for certain frequencies. a known problem for some older com radios. Antennas had plenty of separation.

 

[airguy]

If the manufacturer says not to mount antennas under the canopy or cowling and not closer than 2' or 8" you should heed their instructions. It might and probably will work just fine but you're on your own. Don't call and complain.

I would certainly not advocate ignoring the manufacturers recommendations - but we all (or most of us anyway) also recognize that there is a large amount of CYA involved in those recommendations that is not compatible with experimental aviation.

 

[GKC Aviation]

As an aside to this. In our hangar, we have a FlightRadar24 receiver that uploads data to FR24 (due to being in a remote location). This has been operational for about 5 years. We started having problems with our C560 Citation not being able to get any satellites while sitting out the front of the hangar, but would get a lock before it reached the end of the runway for takeoff. Thinking it was an aircraft problem, we swapped antennas and did a fair bit of fault finding without success. It was found quite by accident, that if the FR24 receiver in the hangar was turned off, all the satellites would return. We subsequently found out that the FR24 receivers GPS puck has a rubbed through cable that was shorting onto the hangar roof. Disconnection of the GPS antenna solved the problem. We also discovered that all the operators near us were having the same problem. Oops!

 

[DBRV10]

Perhaps I should have stated more clearly, the two feet rule is a bit of "catch all" encompassing other antennas also. The various manufacturers all say something different, but pretty much the same. Just because one gets away with it does not mean all do. So I would not be condoning the kind of arrangement as show in the image above.

A real world example, last year, an RV8 owner was having GTN650 loss of satellites in flight whenever the GTN radio was tuned to 121.20. Notch filters, cable checks.....Garmin tech support....... and this was not one of my installations, so i went to take a look. Sure enough the GTN and Dynon antenna were approximately 4-5" apart. I suggested to prove my theory, wire via the connector a switch on the power supply of the Dynon antenna and go fly it, watching the satellite performance page when turning the Dynon GPS antennae on and off. Proven. Move GTN antenna, as it requires a long Coax length anyway and see if that fixes it was my suggestion. Sure enough. Problem solved.

For clarity, here is the big G manual stuff

1. Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of


the aircraft. If the normal flight attitude is not known, substitute with the waterline, which is


typically referenced as level while performing a weight and balance check. A shim may be used


to level the antenna.


2. The GPS antenna should be mounted in a location to minimize the effects of airframe shadowing


during typical maneuvers. Typically mounting farther away from the tail section reduces signal


blockage seen by the GPS antenna.


a) The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or


any other antenna which may emit harmonic interference at the L1 frequency of 1575.42


MHz An aircraft EMC check (See Section 5.10.3) can verify the degradation of GPS in the


presence of interference signals. If an EMC check reveals unacceptable interference, either


insert a GPS notch filter in line with the offending VHF COM or the (re-radiating) ELT


transmitter, or select a different GPS antenna location.


b) The GPS/WAAS antenna should be mounted no closer than two feet from any antennas


emitting more than 25 watts of power. An aircraft EMC check can verify the degradation of


GPS in the presence of interference signals.


c) To minimize the effects of shadowing at 5 elevation angles, the GPS/WAAS antenna must


be mounted no closer than 9 inches (center to center) from other antennas, including passive


antennas such as another GPS antenna or XM antenna.


3. To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the


antenna closer than 3 inches from the windscreen.


4. For multiple GPS installations, the antennas should not be mounted in a straight line from the


front to the rear of the fuselage, to prevent lightning damage to both antennas in the case of a


lightning strike. Also varying the mounting location will help minimize any aircraft shading by


the wings or tail section (in a particular azimuth, when one antenna is blocked the other antenna


may have a clear view).


A 12 inch center-to-center spacing between GPS antennas is required to achieve the best possible lowelevation


antenna gain by minimizing pattern degradation due to shadowing and near-field interaction.


When practical, 12 inch center-to-center spacing between GPS antennas must be used. If 12 inch spacing


is not practical, the maximum center-to-center spacing possible must be used, but never less than 9 inch


center-to-center spacing. Spacing less than 9 inches center-to-center results in unacceptable antenna


pattern degradation.

 

[swatson999]

Perhaps I should have stated more clearly, the two feet rule is a bit of "catch all" encompassing other antennas also. The various manufacturers all say something different, but pretty much the same. Just because one gets away with it does not mean all do. So I would not be condoning the kind of arrangement as show in the image above.

A real world example, last year, an RV8 owner was having GTN650 loss of satellites in flight whenever the GTN radio was tuned to 121.20. Notch filters, cable checks.....Garmin tech support....... and this was not one of my installations, so i went to take a look. Sure enough the GTN and Dynon antenna were approximately 4-5" apart. I suggested to prove my theory, wire via the connector a switch on the power supply of the Dynon antenna and go fly it, watching the satellite performance page when turning the Dynon GPS antennae on and off. Proven. Move GTN antenna, as it requires a long Coax length anyway and see if that fixes it was my suggestion. Sure enough. Problem solved.

For clarity, here is the big G manual stuff

121.20 is an odd harmonic of the GPS frequency, and known to interfere with GPS signals (I've seen the same thing, on the same frequency, on a 530). In fact, though this is from the 530W/430W installation manual, it's no doubt in the 650/750 manuals, too:

VHF COM Interference Check
[Bunch of stuff about non-aviation radios redacted].

Once the Signal Acquisition Test has been completed successfully, perform the following steps:
1. View the Satellite Status Page and verify that at least 7 satellites have been acquired on the 400W Series unit.
2. Verify that the GPS “INTEG” flag is out of view.
3. Select 121.150 MHz on the COM transceiver to be tested.
4. Transmit for a period of 35 seconds.
5. Verify that the GPS “INTEG” flag does not come into view.
6. Repeat steps 4 and 5 for the following frequencies:
25 kHz COM Channel Spacing
• 121.150 MHz
• 131.225 MHz
• 121.175 MHz
• 131.250 MHz
• 121.200 MHz
• 131.275 MHz
• 121.225 MHz
• 131.300 MHz
• 121.250 MHz
• 131.325 MHz
• 131.200 MHz
• 131.350 MHz

7. Repeat steps 3 through 6 for all remaining COM transceivers installed in the aircraft.

(Emphasis added).

So this should have been caught on the ground during the post-installation test.

BTW, I have my Garmin and Dynon SV GPS antennae right next to each other on a shelf under the cowling, and have had no issues. YMMV.

 

[DBRV10]

I see you have found the manuals

And yes you would think that it would have been found on the ground, but for some reason it was not. Remember he had Garmin tech help here, and notch filters etc.

It was not until I asked for the two to be separated that the problem went away completely.

My Mileage varies a lot from your experience. Close together, not a direct and clear view of the sky, and hot location. Not exactly what the manufacturers intended.

 

[GalinHdz]

BTW, I have my Garmin and Dynon SV GPS antennae right next to each other on a shelf under the cowling, and have had no issues. YMMV.

<Emphasis added>

 

[swatson999]

I see you have found the manuals

And yes you would think that it would have been found on the ground, but for some reason it was not. Remember he had Garmin tech help here, and notch filters etc.

It was not until I asked for the two to be separated that the problem went away completely.

My Mileage varies a lot from your experience. Close together, not a direct and clear view of the sky, and hot location. Not exactly what the manufacturers intended.

Yeah, it seems to be a mixed bag...lots of people report no issues, others report having to move one or more to a different location. I have 3 fellow builder buddies (RVs) who all put theirs on a shelf under the cowling, and no issues whatsoever (flying 7 to 12 years). So although not guaranteed, it seems to work for enough people it's worth trying.

GPS interference from various ATC COMM frequencies is *well known*, written in the manual and should be tested. Post-installation tests tend to get overlooked because guys get anxious, it *looks* like it's working great, and they want to get on with other things and/or go fly and play with it ASAP.

Looks like one of the antennas was picking up the interfering frequency and re-radiating it to jam the nearby antenna. I know that some ELT antennas can do the same thing. Good job on figuring out that's what was doing it...not an easy problem to diagnose.

 

[DBRV10]

As a Dynon Authorised dealer and installer, I cannot endorse doing these things. It only has to give trouble once, somewhere in the world, and it is then a bad idea. Regardless of how many successful outcomes. Those who fly in the central USA might be fine, but get into latitudes where the view of the satellites is not as directly above, and then the performance might suffer.

My other concern with clients GPS antenna located under the engine cowl is temperature limits. 60dC is not all that hot, and easily achieved especially after landing.

Just because people do it and get away with it, does not make it a great idea. I will never recommend it, especially if it is a primary nav source.

 

[jakej]

some listen, read, take note & make up their own mind. the smarter ones know that for IFR they would not mount a single Gps antenna in the cowl area. VFR ? who cares ? if the antenna fails they can always just look out the window or at an ipad etc.
BTW - my Gps antenna has survived for 5yrs/600+ hrs under the cowl & always has worked faster/better than the Gps WAAS unit in aft fuselage.

 

[swatson999]

And therein lies the beauty in experimental aviation...we are free to try things and see if they work. In this case, for me (and hundreds if not thousands of others), yeah, it did and does, in fact supremely well, for around 800 hours now.

 

[DBRV10]

Jake, the SV GPS will ALWAYS work faster and better than the one connected to your IFD. Or a GNS/GTN for that matter. Its all that "certified" integrity stuff going on that makes seem that way.

200 or so years ago, any world renowned botanist would declare "all swans are white". That was fact and indisputable. Until one day some Dutch folk found black swans in what is now known as Perth Western Australia.

Same applies here.