ICOM A200 - Weak transmission, lots of static - what to do?

My ICOM A200 has, so far, been reliable and easy to use. But last week the tower at Tacoma Narrows told me that I was garbled, weak, and had lots of static in transmissions when approaching the airport traffic area. Ground communications on 121.8 were loud and clear.

Prior to this, I had a couple flights where I picked up some odd interference on Tacoma's tower frequency, 118.5. One time, it sounded like someone had a stuck mike switch, because the frequency was full of engine-noise like sound. On a couple other occasions, on the same frequency, it sounded like some kind of marker beacon or the like spilling over onto the tower frequency.

Yesterday, I flew to eastern Washington and got radio checks at different airports on various frequencies. Everyone seemed to hear me loud and clear, and Seattle center and Seattle approach both thought I sounded fine.

Reception on all frequencies has always been great, and continues to be good even on Tacoma's tower frequency.

I am using 45 degree bent whip antenna mounted under the fuselage just to right of center. Previously, Tacoma tower has always heard me loud and clear, and as noted above, reception has always been excellent. Antenna connections, etc. were all checked 25 hrs ago at annual and were fine.

I use a Lightspeed 20XL headset, and when I transmit the sidetone sounds pretty normal in the earphones.

From all this, my amateur thinking is:

Antenna and cable are probably OK, given excellent reception and good radio checks on other frequencies;

Headset mike must be OK if the sidetone comes through normally;

ICOM maybe has something going belly up on the Tacoma tower frequency (I"ve heard of radios having problems on just one or two frequencies, and working fine on others).

I have another pair of Lightspeeds that I will use just to rule out mike problems, but in the meantime, does anyone have any ideas/suggestions for how to track this down? I thought it best to do some thinking, and get some feedback, before tearing into everything . . . TIA

Tacoma tower

It's probably the Tacoma Aroma blocking your frequency! But kidding aside have you tried having someone else in an aircraft or base station talk to you on that same freqency? (far enough away from Tacoma of course)
K Shannon
Seabeck WA
HR II under const

Not yet - maybe today!

Have not tried that yet, but may get a chance to run down there today and give that a shot. I'll also try the other Lightspeeds too, just to make sure it is not a mike problem.

I'm just REALLY trying to avoid ripping into wiring harness, etc. until I have a solid idea of where the problem lies......

Better!

Took a short hop today using my older Lightspeeds, and Tacoma tower reported loud, but a bit distorted with a little bit of static. Same results on other channels. It was much better, though, than with the Lightspeeds I used last week. I'm going to check the mike gain on the ICOM, and see if adjusting that helps with the distortion.

Reception was excellent, with clear reception of Unicom traffic 75 miles away, and a couple of radio checks from nearby uncontrolled fields were "loud and clear" as well.

Seems as though the Lightspeeds I was using last week may be the source of the problem. I sense more "in flight testing" ahead to make sure, though.

Icom

It is not likely that your radio doesn't work on individual frequencies and appear good on others. Modern radios are synthesized and if one freq works they typically all will be good. The problem is most likely the modulation setting of the radio along with the adjustment on the mike on your headset. Many times the gain on the headset mike is not set up to be optimal with your radio and the best way to solve your problem is to pull the radio and have a shop set the modulation and then check it with your headset. The gain on the headset should be turned down to around 1/4 of it's adjustment. As a last measure to make your radio sound really good you should order the microphone covers from Oregon Aero because the noise cancelling mikes on your headsets will start to act up at around 98 decibals which is right around the level where our RV's live. By using these covers you will probably get comments from controllers at your home field who are used to the way you used to sound when you would call. Without these covers you will most likely notice the mikes acting up if you have an intercom as the squelch breaks and then quiets, over, and over, and over!

Now that I've offered that advice I'll give you a different way of doing this that will cost you nothing. Pull the radio and on the top you will find a hole with a shiny sticker over it labeled modulation. Use a razor blade to lift one side of this sticker and note how the pot underneath is positioned. Use a pen to mark the postion of the pot on the top cover so that you can return it to this position exactly if you don't like the results of the adjustment. Take a jewelers screwdriver and make a small adjustment of about 1/8 turn and note the direction of the adjustment for future. If this helps to make the transmission sound better stop here. A little does a whole lot and you don't want to overdo it or the radio will sound garbled, kind of like Charlie Browns teacher if you remember how she sounded. (I had to do this with my Icom)

Good luck,

Ditto what Bryan said. A200's are not well set up for the high noise environment of an RV, out of the box. Adjust the modulation (may be labled "Mic Gain" depending an vintage of the radio) until the tower hears you. Once that is set, adjust the "Sidetone" down until it no longer deafens you.

The A200 is a great radio and the best bang for the buck out there, but it takes some tweaking to make it work well in an RV.

I would also look at the back of the AeroElectric connection. In the chapter on 'compatibility' there's a couple of paragraphs about resonance issues creating garbled transmissions on certain frequencies. Lectric Bob explains that this is more common in composite aircraft -- but I think it's something worth considering.

Good Tips!

Thanks Jeff, Bryan and Jamie for the suggestions - I have the ICOM out of the rack, and am familiar with the adjustment pots being under the metal stickers. I'll also check out the Oregon Aero mike covers.

The mic gain adjustment on the ICOM must be at least close, because the tower reports hearing me "loud, but a little distorted and with some static". The fact that the old Lightspeeds sound better than the new ones tells me that perhaps the mic gain setting on the new pair (which is adjustable) is not the same as on the old ones. If I can get those equalized/matched, and then set the ICOM's gain/modulation pot to the optimum setting, then hopefully I'll be good to go no matter which headset I use on any given day.

I'll report back after further testing.

Problem Solved

I installed the Oregon Aero microphone muffs, and then had the technician at the local avionics shop check the ICOM settings, etc. What he found was that the ICOM's squelch was set too low (i.e., you could break squelch with less noise than specified), but the ICOM's gain and sidetone were fine. The newer Lightspeeds I had turned out to have their mic gain set to MAX, whereas the older pair was set in the middle. We set the new Lightspeeds to have "medium" mike gain, and that was it. Also had the SWR for my antenna system checked, and it was 1.4 at 118 MHz and 2.6 at 136 MHz, so everything was OK there.

Now, Tacoma Narrows tower says I sound loud and clear, and things seem to be working fine. The radio does sound a bit cleaner through the headsets with the mike muffs on, though not a huge improvement.

mic gain on Lightspeeds..

John,
How do you set the mic gain on the LightSpeeds ? I have the same headsets but don't have them in front of me.

Thanks

John