Garmin WAAS antenna issue

[mschmuff]

Hoping someone out there can help me out with this.

I just had an avionics install done - brand new WAAS 430, brand new antenna, brand new everything 340/327 etc....My avionics guy told me my wiring was in bad shape throughout and replaced everything so we were starting fresh.

 

In the first month I started losing the satellites until finally I was getting none.  The Comm and Nav work fine, it just won't acquire the satellites.  I sent the antenna back to Garmin and they gave me a new one.  Within 3 months I am experiencing the same thing again.  I have pulled the unit, cleaned the connectors, tested the amps to the antenna and everything is as it should be.

Today on my flight home from work everything worked great for the first 20min, next 10min - no signal, then final 10min everything reacquired...... 

Could I have yet another bad antenna?

Is my 430 eating or burning up antennas?  Is that even possible?

Has anyone experienced this before?

 

Thanks for your help!

[orionflt]

check the coax cable, make sure it is the correct cable for the waas upgrade (RG400 or RG142B/U) RG59 is not acceptable. also check the ends on the coax and make sure they have been properly installed, if they are crimp type and the crimps are weak or the ground was srtipped too far back it can give you the intermittent connection you are describing.

 

Brian 

[Cruiser]

what does your avionics guy say?

 

Your post sounds like it is slowly deteriorating? or is it intermittently not getting a good signal? 

[mschmuff]

My avionics guy removed the coax from the original install and replaced all of it, new ends and everything.  He has spoken directly to his contacts at Garmin and they are "stumped".

They said it may be an interference issue with the GDL-39 or Comm freqs.  They also said it may be another bad antenna......

I'm going to remove the GDL39 for my flight back tonight but failing that I will probably end up send the antenna back for another new one. 

[OR75]

a bjt scary since , if i understand well, when you have a GPS WAAS, you can get rid of all other navs

[Piloto]

Do you get GPS signals on the ground? If you do you may be experiencing GPS interference from an outside source.

Check your NOTAMS for your area.

I just got this one https://www.faasafety.gov/files/notices/2013/Sep/Cape_Canaveral_13-02_GPS_Flight_Advisory.pdf

 

Check for onboard interference by turning off different equipment. At the antenna cable connector verify you are getting at least 3VDC with 430 on..

 

José

[mschmuff]

I have a 696 on the yoke and every time I spool up the 430 and don't get a signal - the 696 has a great signal.  And yes, when I am on the ground and the unit is working I get a great signal on both....

[DrBill]

You may be getting some interference from another device.  A few years ago, I worked on a special miniature hard disk drive for GPS applications. We gave Garmin about 50 pre-production models and they worked great.  When I replaced them with production, the GPS would not acquire. Turns out in their great wisdom, the development team changed the clock frequency in the drive and the new clock was an exact multiple of the GPS carriers.  The new HDDs were causing a de-sense in the GPS and it could not "hear" any satellites. Your symptoms sound exactly like that.  Same thing if you had an intermittant coax connection.

 

BILL

[takair]

Lots of good advice above. Jose mentioned the voltage. Worth checking, I thought nominal was 5vdc. Too high and it can take out the antenna. It is possible, even likely that the problem is not the antenna, but the 430. You may want to try another Or send yours in to Garmin. Hard to explain why the antenna seems to fix it short term. Those antennas are quite reliable. As I recall, not only should the coax be a specific type, but also has a minimum length. In a Mooney the re would be a tendency to shorten it. I don't think this would cause the failure...I don't recall the reason....but I seem to recall that Garmin was very specific. Regarding interference, if able, try shutting off other systems. You can monitor the satellite page to see if anything has an impact.

[carusoam]

One of the first challenges I had seen on Mooneyspace years ago was a Garmin Antenna problem with dual antennae.

I believe it was a problem with the antennae. But I don't remember anything that well anymore.

Hopefully this gives you something to search for....

Do our records go back that far?

Good luck,

-a-

[Alan Fox]

You may have a "leaky" transmitter , I would check the shielding / grounding  on all the transmitting antennas......Pay close attention to the DME and Transponder as they transmit constantly , The DME whenever on , and the transponder , whenever interrogated.....

[Marauder]

You may have a "leaky" transmitter , I would check the shielding / grounding on all the transmitting antennas......Pay close attention to the DME and Transponder as they transmit constantly , The DME whenever on , and the transponder , whenever interrogated.....

Try flying without any other hardware on. See if that makes a difference.

[chrisk]

I had a similar problem. I recently had a GTN650 installed. It worked on the flight home from the avionics shop, and the next flight. The third flight, it kept dropping the GPS satellites, but only when flying. Everything was fine on the ground. Turning off everything else made no difference. The plane went back to the avionics shop. A new antenna did not fix the problem. Replacing the GTN650 with another unit did.

[mschmuff]

Great info!!!

I flew to work tonight and everything worked. I left the satellite page up the entire time and shut things off one at a time; GDL, Comm2....no change in satellite reception.  I didn't shut off the DME so I'll try that tomorrow.  One strange thing was that I never got more than 2 bars of signal on any given satellite.  I had 15 satellites but only up to the first or second line.....once on the ground and shut the aircraft off the bars got stronger?????   

[N601RX]

Coax can look fine and have problems in certain frequency bands. If you shop has a network analyzer ask them to sweep the GPS coax across the GPS band.

[Marauder]

Another thing to consider since you mentioned this is a new install. Where are your antennae respective to each other? You could be experiencing interference this way. A good avionics shop knows this, but sometimes they either don't or get lazy.

[Piloto]

Great info!!!

I flew to work tonight and everything worked. I left the satellite page up the entire time and shut things off one at a time; GDL, Comm2....no change in satellite reception.  I didn't shut off the DME so I'll try that tomorrow.  One strange thing was that I never got more than 2 bars of signal on any given satellite.  I had 15 satellites but only up to the first or second line.....once on the ground and shut the aircraft off the bars got stronger?????   

That is a very good observation that may pinpoint to the root cause. Next time while in flight and watching the satellite signals, switch magnetos, turn the alternator field off and on, turn DME off and on, transponder off and on while watching the signal bars. Allow 15 seconds for the bars to react to the changes. 

 

On a normal installation the satellite bars will go all the way to the top line. If the antenna is not receiving the 5VDC it will receive a weaker signal. On the BNC cable connector at the 430 verify that the center pin tip protudes even with the ground ring. Check also the antenna connector. Because of the high frequency the center pin does not need to be in contact for the signal to couple through but it needs to be in contact for the 5VDC.

 

You will have a good installation when most of the bars reach the top line. A weak satellite reception may impair the 430 from declaring an LPV approach.

 

José