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GNS 430 reception problems



 
 
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  #11  
Old September 8th 06, 12:41 AM posted to rec.aviation.owning
Kevin Clarke
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Posts: 147
Default GNS 430 reception problems

Thanks everyone for their feedback and opinion. I am now convinced what
is going on is a simple case of demonic possession.

We swapped the antennas. No difference
Tonight we replaced the BNC connector; no difference.
We tested it with and without the KX-155 on; no difference.

When running the recv sensitivity test, the KX drops out much later than
the GNS.

So I am left with demonic possession.

I'm thinking I need a new avionics guy. Unless someone has a wild idea.

thanks,

KC

Kevin Clarke wrote:
Hi,

I'm looking for folks that might have a similar experience. Recently
upgraded the panel to include a GNS 430 and replace one of those old
NARCO all in one VOR instruments plus an old NARCO radio.

Anyway great upgrade. The GPS function works wonderfully. Filing /g is
the best. The NAV function works great. Dual glide slope indicators(the
other is slaved to a KX-155) really makes IFR manageable.

The problem is the COM function of the GNS 430. We're only getting about
40 miles of range on the receive side of the COM. I'll call for flight
following on COM1(the GNS) and never get an RX indication. When I flip
over to COM2 (the KX-155) it works just fine. The KX has a range of at
least 80 miles. The GNS seems uneven. We can xmit and be heard over
distances but the receive side is really only useful in and about the
terminal area. This is less than optimal.

When we did the upgrade we kept the original antennas that were on the
plane(PA28-180).

Our avionics guy is baffled, maybe useless at this point. He swapped out
the GNS plus ran a myriad of other tests. He says everything is checking
out just fine. But that is surely not our experiences. So I turn it over
to the collective wisdom of the net. Has anyone else ever experienced
anything similar?

Thanks.

  #12  
Old September 9th 06, 06:29 AM posted to rec.aviation.owning
[email protected]
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Posts: 44
Default GNS 430 reception problems


On 7-Sep-2006, Kevin Clarke wrote:

When running the recv sensitivity test, the KX drops out much later than
the GNS.



Was the RX sensitivity test done on the bench or in the airplane? How "much
later" (in dB)? If it's more than a few dB then the GNS 430 is probably
defective. There should be a published specification for receive
sensitivity, which will be shown in the Garmin shop service manual if
nowhere else. If what you get, with a bench test, does not meet spec then
troubleshooting needs to move to internal circuitry. Probably best done by
a Garmin authorized repair facility if there is such a thing.

Good luck!

-Elliott Drucker
  #14  
Old September 9th 06, 08:10 PM posted to rec.aviation.owning
[email protected]
external usenet poster
 
Posts: 44
Default GNS 430 reception problems

No way the sensitivity difference between the two radios should be 20 dB --
that reflects an incident signal strength difference of 100-fold! If the
Garmin is not defective (and the unit swap seems to confirm this) then the
receive signal is being attenuated by roughly 20 dB someplace. This should
be fairly easy to find using a spectrum analyzer or similar instrument,
again something any avionics shop should have available.

However, I must wonder why your avionics shop isn't going through these
rather obvious diagnostic steps without outside help.


-Elliott Drucker
 




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