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Strange radio problem A210

C

Chappyd

Well Known Member
Just when I thought my avionics install was all wrapped up............Tonight I was playing with the radios and noticed that when I transmit on my #1, a Garmin SL30, my #2 , an Icom A210, recieves it, no matter what frequency it is tuned too!!! In other words, the A210 always receives everything the Garmin transmits. It only picks up the tuned freq when transmitting on my handheld outside the plane.

Any Ideas??
 
Chappyd said:
Just when I thought my avionics install was all wrapped up............Tonight I was playing with the radios and noticed that when I transmit on my #1, a Garmin SL30, my #2 , an Icom A210, recieves it, no matter what frequency it is tuned too!!! In other words, the A210 always receives everything the Garmin transmits. It only picks up the tuned freq when transmitting on my handheld outside the plane.

Any Ideas??
Click to expand...

That does not make sense. No radio will receive a signal not on its set frequency, except for a harmonic jump to a TV audio reception sometimes.

I would suspect a voice feed back via interphone is being heard through the A210.
 
Chappyd said:
Just when I thought my avionics install was all wrapped up............Tonight I was playing with the radios and noticed that when I transmit on my #1, a Garmin SL30, my #2 , an Icom A210, receives it, no matter what frequency it is tuned too!!! In other words, the A210 always receives everything the Garmin transmits. It only picks up the tuned freq when transmitting on my handheld outside the plane.

Any Ideas??
Click to expand...

I take it that the reverse is not true, where if you transmit on the Icom, the Garmin will not break squelch?

Your antennae are just a couple of feet away from each other. You are transmitting from one antenna to the other with about 7 W of power. You may well be overloading receive filters and amplifiers of the Icom, and it basically all passes through (even off-frequency).

If the above does not happen in the Garmin unit, then that means that they have a more robust filter / demod design.

When you transmit with the handheld unit outside the aircraft, you are using less power, and are further away from the Icom receive antenna than in your previous case. The filters on the Icom receive section can now tolerate that lower power level.
 
Lycosaurus said:
I take it that the reverse is not true, where if you transmit on the Icom, the Garmin will not break squelch?


Your antennae are just a couple of feet away from each other. You are transmitting from one antenna to the other with about 7 W of power. You may well be overloading receive filters and amplifiers of the Icom, and it basically all passes through (even off-frequency).

If the above does not happen in the Garmin unit, then that means that they have a more robust filter / demod design.

When you transmit with the handheld unit outside the aircraft, you are using less power, and are further away from the Icom receive antenna than in your previous case. The filters on the Icom receive section can now tolerate that lower power level.
Click to expand...


That is correct, the Garmin seems fine and acts normally. My antenna locations are close, but no closer than others I've seen, located just behind the rear spar on either side of the fuse. I didn't measure it, but it should at least 36"

David- The Icom has a little "Rx" that lights up when it is receiving, and the light comes on when this is happening. That leads me to beleive the radio is actually receiving the same as if it were set to the proper frequency.

I didn't notice this when I first did the wiring, but it even happens when com 2 is not selected on the audio panel, selected for listening that is. I'll have to check, but is it possible that the intercomm feature is involved?I'll have to investigate further, I just noticed this when I was on my way out of the shop last night


I may yet trash this radio in favor of the SL40
 
Just thinking outside the box here...

You did not accidently have the dual watch feature activated with the standby channel set to the same freq as the Garmin did you?
 
I'm pretty sure I didn't. At first I thought I did, but then i started changing freq's and it was still happening. I looked at the Icom operator's manual this morning, and saw that the "RX" light will come on when the squelch opens (not sure what that means) in addition to when receiving on the frequency. So I'll look into that further tonight when I get home.

I'll also scroll through all the settings and check them

Thanks for the ideas guys.
 
Interlock

I was noticing last night in ICOMS wiring instructions, a sentence or so about transmit / receive interlock when using 2 radio and antennas that are close together. I'd go back and give that a look if I were you.
 
Another check point...

There is also a possibility that the Garmin is at fault. The Garmin transmitter may be bleeding over the frequencies. How does you hand-held react when set to the same frequency as the Icom? Just a thought.
 
The handheld behaves normally. I went down to the shop, went through all the menu settings on the Icom. Came back up to the house and called Icom support. The Rep I spoke with says, "oh yeah, that's very common." Said I should have some kind of RF switch that breaks the connection on the Icom when I transmit on the Garmin. Of course, while very courteous he had no clue about a solution, just extremely vague suggestions.

Doing a search on rf switches, both here and on Google leaves me no smarter :(
 
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.
 
Chappyd said:
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.
Click to expand...

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
 
radio geek

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 :D

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.
 
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!
 
DANGER WILL ROBINSON!!

Chappyd said:
the antennas were not connected when I first tried the radios and the PTT functions.
Click to expand...

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
 
Last edited:
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
 
SteinAir said:
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
Click to expand...

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?
 
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!
 
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.
 
Chappyd said:
Swapping antennas swapped the problem.
Click to expand...

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
 
Dave, glad to hear you finally found the problem. I didn't mean to harp on you personally about transmitting with the antennas disconnected, but every time we send one back to Garmin to get repaired (and we do regularly), they chew my behind for "letting customers do that over and over" and this was a good excuse to drive the point home again. Luckily it sounds as if you didn't blow anything up.

Thanks for sharing your issue. It's not a cheap one to fix, but it does again go to show that 99.9% of the time these issues are caused either by install or wiring, almost every time (even with those of us that do it for a living). Nobody wants to think it was caused by them, but it usually is. I don't say that to make anyone feel bad, just to help them understand why sometimes the tech support people at the mfgrs seem less than overjoyed to help troubleshoot problems.

Anyway, I'm glad you're on your way and on the downhill slide to your first flight.

Cheers,
Stein
 
More than happy to report on my issues. Hopefully at some point the info can help others down the road. Very relieved to have everything working properly BIG :D. Stein, sent you a pm......
 
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