RX feedback in my A210 from the GPS...

Wicked Stick · Post by **Wicked Stick** » Mon Oct 20, 2008 8:44 pm

Just finished installing my entire panel in the plane. (RV-8)

Last night I turned everything on and started playing with it and setting it all up so that they all talk to each other. (GPS, EFIS, Autopilot, Radios)

I'm getting some random static reception on my I-Com 210 and it seems to be coming from my Garmin 496 GPS. It's worse on certain frequency ranges but it's there nonetheless. It only shows up when the NMEA In/Out options are turned on in the GPS setup. I know this allows the GPS to feed the radio with frequencies of the "direct to" airport and surrounding air traffic control numbers, but I'm not sure why it also seems to feed it static on the comm frequency.

I have the following in my panel. AF3500 EE, PMA9000EX intercom, SL30, I-Com210, GTX327 transponder, ADI Pilot II and the GPS496.
Everything is hooked up via a Fast Stack Hub with their pre-made wiring harnesses. I have all the grounds located in one spot.

Any suggestions on why ?
Also here's a thought I will look into.. Could it be the squelch is too sensitive ? Will look into that for now.
__________________
Dave "WS" Rogers
FFI wingman certified
RV-4 N97RT (Flying)
RV-8 N173DR (Finish Kit)

Post by **Spike** » Tue Oct 21, 2008 5:47 am

Does this mean that it occurs when transmitting on a Comm freq with the Icom?

John

Wicked Stick · Post by **Wicked Stick** » Tue Oct 21, 2008 10:34 am

Hi Spike,

No, sorry for the confusion. What I get is a "recieve" signal of static when I'm just listening in on the freq.

dons · Post by **dons** » Tue Oct 21, 2008 1:45 pm

I don't know how easy this would be for you to try Dave, but I would enable the NMEA feature on the 496 and remove the pin in the harness connector at the 496 for the serial out. If the 'static' goes away, I suspect some form of crosstalk from the serial data line. It could be something in the audio range of frequencies, but since you say it varies with the 210 tuned frequency, it sounds more of an RFI gremlin.

The solution if the above is the case could still be quite a few things, but here are some ideas:
1) check the general grounding of the Fast Stack Hub system, they may have suggested some special ways to ground or not ground the Hub
2) check that the audio lines are properly grounded and a shield isn't broken where it shouldn't be (I'm guessing the pre-made harness uses shielded wires for audio) - a lot of audio systems will only ground one end of a shielded cable to prevent ground loops, the electrical type

- This is more if it is an audio interference and not RFI
3) use shielded wires for the data output of the 496 to where ever it goes, not a great solution but it would likely work
4) ask the Fast Stack Hub people if they have heard of this and what someone else did to eliminate it - if it is a data line induced noise problem, they likely have some good ideas what to look for - make sure you mention the disconnecting of the data line at the 496 if you were able to do this
5) here is a 'black magic' type of thing I used a long time ago where a serial data line was causing noise - I put small (few hundred pico-farads) capacitor between the data line and ground close to the driver (i.e. the source of the data, the 496 here) to reduce the high frequencies that might be piggy backing on the data signal

If disconnecting the data output at the 496 doesn't eliminate the 'static' with the NMEA turned on, my guess is some form of RFI from the 496 getting into the 210. Checking the grounding for the 496/210 is somewhere to start, but this type of problem can sometimes be a wee bit difficult to solve.

It might also be RF is leaking out via any number of wires in the harness coming from the 496, if this is the case, some small capacitors on non-antenna leads to ground may solve the problem.

Bottom line, check some easy things like grounding, then ask the FAST STACK people for suggestions as I'm sure they know something about this kind of issue.

Wicked Stick · Post by **Wicked Stick** » Tue Oct 21, 2008 9:09 pm

Don,

Thanks for all your suggestions. I will try them each as needed by order of easiest to more involved.

Today I went back and sat in the plane and went through the book on the A210 and found you could adjust the Squelch so I set the Squelch from 0 to 1 in the settings menu. After having done that, it seems to have solved my problem. I played with everything for about an hour and I never got the static RX to show up again. And, with the squelch adjusted I can still receive good transmissions from inside my garage with the belly antenna to aircraft flying about 25 miles away.

Post by **Spike** » Wed Oct 22, 2008 8:13 am

Excellent!

dons · Post by **dons** » Wed Oct 22, 2008 2:30 pm

Those kind of solutions I like! Fixing bad RFI is a real pain most of the time.

Wicked Stick · Post by **Wicked Stick** » Thu Oct 23, 2008 12:16 pm

Just a bit of extra info.. The Squelch on the A210 has a range of -10 to +10 and the factory setting is zero. So I think setting it to 1 or 2 shouldn't reduce the range of reception to much. (I'll know for sure when I get flying).

Anyone else who is flying with one already, know they have had to adjust theirs from the default of zero ?