Strange radio problem A210 - Page 2

L.Adamson · #11 01-15-2009, 08:24 PM

Quote:

Originally Posted by Chappyd

Degdemon, I just noticed your post when I was replying to this thread again. I went and looked at the wiring instructions, and it does indeed make a reference to having 2 radios in the plane. It says to connect pin "N" to pin "9" on each radio. While the pin locations are for 2 Icom's. Pin N is the interlock feature, while "9" is the PTT+ on the other radio. I suppose I should throw a wire between these 2 and see if that solves it. I imagine that the incoming signal from the garmin would tell the Icom to "shutoff". I'm suprised the Icom tech didn't mention the interlock function.

I'm just finishing the wiring of an audio panel, Garmin SL-40 & Icom A210. The antennas are about three feet apart (under the seats). Hopefully this will be done by Sunday, and I'll report the results, if your problem isn't remedied by then. BTW--- I didn't wire an interlock function, either; since they were not both Icoms.

L.Adamson

IowaRV9Dreamer · #12 01-15-2009, 09:41 PM

I'm an ex-radio designer. Sounds like the ICOM doesn't have a very good front end design, and likely a somewhat simple squelch circuit as well. The off-frequency strong transmit signal from the Garmin is getting through the filters, and even though it is mixed to an incorrect frequency, it is so strong that it pushes the IF strip around and the radio "hears" a signal that appears to be on frequency. If the squelch circuit is old-school / analog it will get fooled and open up and let the audio signal out to your ears.

The other possibility is an IF injection problem, where even a radio with a great front end can get interfered with by a strong local off frequency signal. The effect is very similar. Both of these problems are not uncommon in AM radio.

In either case, there isn't a lot you can do. First I'd make sure that you had a good connection to the transmitting antenna (and also that the antenna was good / correct type). If you don't, you'll have a bad SWR and the whole problem will be worse. Moving antennas further apart will help a lot - I plan to put my COM2 (if I have one) on the top of the aircraft while COM1 will be on the bottom.

Assuming the antennas don't solve your problem, you can hook up the interlock. Bascially it willl prevent the ICOM squelch from opening (which means letting audio through the radio) whenever you are transmitting on the Garmin.

Has anyone else had this problem? It's not a big deal, certainly fixable with the interlock connection, but as a radio snob it would bug me

Good Luck!

BTW - if you spend a lot of quality time testing radios, you will learn to appreciate the older radio receiver designs (KX170, etc). Much better than the new stuff. Great receivers, but big heavy, limited features, etc.

Chappyd · #13 01-16-2009, 03:29 AM

Thanks for the input.

L- I'm looking forward to hearing your results, as my antenna are in the same location.

I did try to do a quick test to see if the Interlock would work, it seems to, but I need to spend more time and do a decent hook up to be sure. I also was suprised that I didn't notice this before. After reading Iowa's post, it ocurred to me that the reason I may not have noticed it was the antennas were not connected when I first tried the radios and the PTT functions.

Appreciate all the info!

IowaRV9Dreamer · #14 01-16-2009, 09:26 AM

Quote:

Originally Posted by Chappyd

the antennas were not connected when I first tried the radios and the PTT functions.

As a radio guy - this makes me cringe. I'm not saying you did this, but as a public service:

NEVER operate any transmitter without either a correct antenna or a dummy load attached. If you do, all the transmit energy has nowhere to go and it "bounces back" off of the open BNC connector and hits the final transmit device which is usually a fairly stressed out transistor. The RF voltages get really high and you can easily blow your output stage.

Even though our COM transmitters are pretty small (5-15W) you'd be amazed how much RF voltage there can me. A 10 watt transmitter into a good load or antenna produces peak-to-peak RF voltages of about 63V! That voltage doubles if you have a bad antenna (or no antenna). You can see why things can blow out.

Some transmitters have protection against this (sometimes called SWR protection) but don't rely on it. Use a good antenna or a dummy load rated for the power.

Sorry for the rant - not personal - just don't want to see innocent transmitters injured!!

H

SteinAir · #15 01-16-2009, 02:08 PM

Ditto...it's worth repeating and should be taken as gospel. Just to repeat:

DO NOT transmit on your radios without the antennas (or a known load) hooked to them....BAD gremlins move in and the majority of the time you will at least do significant damage to something.

Not much more to add to this thread - but obiously something "ain't quite right", because there are plenty of people with both Garmin and ICOM's installed with antennas installed in similar ways that are not having a problem. Naturally, I'd suspect the wiring/install first, units last...but something is wrong (aren't I the master of the obvious).

Cheers,
Stein

Mike S · #16 01-16-2009, 03:04 PM

Quote:

Originally Posted by SteinAir

Naturally, I'd suspect the wiring/install first, units last...but something is wrong (aren't I the master of the obvious).

Cheers,
Stein

HMMM this one isnt even worth the standard dos centavos??

Chappyd · #17 01-17-2009, 09:43 AM

Quote:

Originally Posted by SteinAir

Ditto...it's worth repeating and should be taken as gospel. Just to repeat:

DO NOT transmit on your radios without the antennas (or a known load) hooked to them....BAD gremlins move in and the majority of the time you will at least do significant damage to something.

Not much more to add to this thread - but obiously something "ain't quite right", because there are plenty of people with both Garmin and ICOM's installed with antennas installed in similar ways that are not having a problem. Naturally, I'd suspect the wiring/install first, units last...but something is wrong (aren't I the master of the obvious).

Cheers,
Stein

Ok,Ok, I get it. I went back and looked through the entire Garmin and the Icom manuals and didn't see any warning about transmitting without the antenna. I understand you guys know what you're talking about, but it sure would be nice to have this info prior to doing the installation. How the **** is someone doing this for the 1st time supposed to know? I take it this is the education part.

ANYHOW.......getting back on topic. I hooked up the interlock wire as called out on the Icom instructions. I still get the rx light on the Icom. If I remove the Icom antenna from the airframe, coax still connected, the rx light doesn't come on off frequency. (I won't/didn't transmit on the Icom with the antenna not mounted to the airframe) This leads me to conclude that the grounding of the Icom antenna is what's permitting this to happen. Or a bad ground somewhere on one of the radios?

Does any of this info help to point me where to look next?

Chappyd · #18 01-17-2009, 03:10 PM

I have found the culprit and it is me! At least I did find something wrong. I bought 2 of the comant bent whip antennas from Stein. When I first recieved them, I didn't have screws the proper length in house. A trip to the hardware store to get the screws of proper length, no problem. Checking them against the antenna revealed the c'sinks didn't match- screws were 82', antenna was 100'. No problem, I'll just csink to match. Bad idea- the csink tool grabbed and took a piece of material out. I patched it up using jb weld , letting it dry and removing the excess, redrilling the hole and c'sunk the new hole. I ordered the proper bolts. It didn't appear that the antenna itself was damaged internally, but apparently it is. Swapping antennas swapped the problem.

So, I have a new one on order. I'm very relieved to have found the problem. I was lying awake in bed at 3 am this morning thinking maybe I would have to tear apart my whole installation and redo it.

Hopefully I'll sleep a little better tonight. Thanks to those who tried to help me out!

Mike S · #19 01-17-2009, 04:12 PM

Dave, thanks for the report.

You just might save someone else a lot of trouble chasing a similar problem.

I always appreciate it when folks post the answer to their problem, gives me a chance to learn something new.

L.Adamson · #20 01-17-2009, 06:14 PM

Quote:

Originally Posted by Chappyd

Swapping antennas swapped the problem.

It's great you found the problem, because I was just going to tell you that my setup worked just fine today.

Garmin SL-40, Icom A-210, PS Engineering 8000B audio panel, 2 Comant antenna's...................and "no" N to 9 jumper wire between radios.

L.Adamson