ICOM A-24 and Bose A-20: Transmit Issues

Tedric

Tedric

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Aug 1, 2021
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Tedric
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KPWT
I've got an older ICOM A-24 handheld (same as the A-6 but with VOR) as a backup, and today I thought I'd test it out in flight with the Bose A-20 headsets I use. I used the ICOM adapter to mate the handheld to the headset, and used the PTT that is on the radio itself rather than adding a remote PTT. The ICOM manual says this works fine, the remote PTT is just for convenience and is designed to be velcroed to the yoke. Antenna was the standard rubber duck from ICOM.

I asked for radio checks on a couple different frequencies of airports in the area that had traffic activity. When I pressed the PTT I got a lot of noise and squeal in the headset, and no response from anyone. Later, I tried when on the ground at KPWT and someone replied that whoever was trying to call, the audio was unreadable. So some kind of signal is getting out.

Reception of local CTAFs and Seattle Approach was OK, nowhere near as good as the Garmin gear in the panel, but good enough audio quality and clarity to do the job.

So, I'm looking for advice on where the transmit issue is. I've seen some headset adapter units advertised as being for the A-20 and certain ICOM radios (the A-24 among them), and I'm wondering if there is some specific circuitry that this combination needs to play nice together, and that the ICOM standard adapter does not offer. Or perhaps something else?

I'm sure a real antenna mounted on the fuselage would be a big step up, but first things first.

And to anyone flying near KPWT today that was annoyed by some ugly noise on frequency for a few seconds - sorry, I want to get rid of it too :-)
 
The A24 has a known problem with RF feedback causing squeal, though Icom has never admitted it. It's absolutely unusable with the rubber duck antenna on the radio; you have to use a remote antenna (though I was successful using the rubber duck on the end of a cable with a Comtronics helmet in my ultralight). I was also successful with a remote installed antenna and a homemade headset in my Fisher. The farther away the antenna is the better, and running the mike and PTT wires through a ferrite bead can help, too.

I believe (could be wrong) that the radio's PTT activates both the headset mike as well as the radio's own mike, which would make for a noisier transmission, whereas the remote PTT just activates the headset mike.

I'm currently using the A24 with a DC headset and remote antenna in my Parrakeet with no problems at all; I can hear fine and everybody can hear me, of course with the usual open cockpit noise, but no squeal. Some say that the DC headsets are less likely to squeal than other brands.
 
If you get a telescopic metal antenna and stick it out a window it kinda works.

The rubber duck inside the aluminum box is impossible in my experience
 
Dana said:
The A24 has a known problem with RF feedback causing squeal, though Icom has never admitted it. It's absolutely unusable with the rubber duck antenna on the radio; you have to use a remote antenna (though I was successful using the rubber duck on the end of a cable with a Comtronics helmet in my ultralight). I was also successful with a remote installed antenna and a homemade headset in my Fisher. The farther away the antenna is the better, and running the mike and PTT wires through a ferrite bead can help, too.

I believe (could be wrong) that the radio's PTT activates both the headset mike as well as the radio's own mike, which would make for a noisier transmission, whereas the remote PTT just activates the headset mike.

I'm currently using the A24 with a DC headset and remote antenna in my Parrakeet with no problems at all; I can hear fine and everybody can hear me, of course with the usual open cockpit noise, but no squeal. Some say that the DC headsets are less likely to squeal than other brands.
Click to expand...
Yeah, I had the same problem.

Icom has a tech support document about it and I have a copy. It will take me a bit to find it. Even doing the mods in that tech doc I never did get things working right.

The remote PTT switch does seem to activate the handheld and headset mics. I think I experimented with plugging in the headset only and not the mic plug. I don’t remember, it was a long time ago. I think I also skipped the remote PTT and used the built in mic/PTT. Maybe that was the trick.

When I used it in the glider I clipped a speaker mic to the shoulder harness and had no trouble.


Edit:

Found it,

 
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Thank you both for this information - I figured I wasn't the first person to deal with this issue. The ICOM bulletin's recommendation for ferrite beads on the cable will be easy enough to do, I'll have to give some thought to a second antenna setup and how I'd want that configured.

Fortunately, I've never had a problem in flight with the COM radio in the plane (ICOM A200 from 2004-2018, GTN 650 since then), but one never knows....
 
Tedric said:
Thank you both for this information - I figured I wasn't the first person to deal with this issue. The ICOM bulletin's recommendation for ferrite beads on the cable will be easy enough to do, I'll have to give some thought to a second antenna setup and how I'd want that configured.

Fortunately, I've never had a problem in flight with the COM radio in the plane (ICOM A200 from 2004-2018, GTN 650 since then), but one never knows....
Click to expand...
The problem with ferrite beads (in my experience):

1) they didn’t seem to work
2) by the time you coil the headset cable to get them clamped, your headset cord is way too short to use.

I decided that if I need to use my A24 in flight I would plug in the headset, leave the mic unplugged, then use the radio’s built-in PTT and mic.

If you are able to get good results with the ferrite beads, please let me know. Maybe I can try again.
 
Matthew said:
The problem with ferrite beads (in my experience):

1) they didn’t seem to work...
If you are able to get good results with the ferrite beads, please let me know. Maybe I can try again.
Click to expand...
When I tried them they made a slight improvement. Mine would squeal, then stop when I moved one of the wires slightly, no discernable pattern to it. Adding the beads didn't completely fix it, but made it take less fiddling. But with the DC headset in the Parrakeet, it's worked perfectly with no ferrite beads.
 
Well that's a practical, physical obstacle to implementing the ICOM suggestion - but I'll have a look. Appreciate the followup on that.
Problem with using the ICOM's built in PTT and mic is that I'm flying an RV-6 and it is one noisy machine inside; I'm skeptical that whatever noise canceling ICOM may have provided on the mic will be able to handle that. One more factor to consider....
 
That was the last only thing I ever found wrong with that iCom. I still have it, and it still lives in my flight bag. I’ve used on the ramp, in the glider, in the towplane, in the rain… I’ve used it hard. But that remote PTT operation generates feedback.
 
There are a couple of ways to add a ferrite choke on a cable, and I don't know what Icom is recommending. One method is to loop the cable through a ferrite toriod X number of times. Another method is to use a clamp on ferrite that's shaped more like a tube. With either type, there are different mixed of ferrite that have different attenuation at different frequency ranges. Somewhere I have a chart of mixes and maybe some info on that.

One of the problems is that typical headset cable lengths can be a pretty good approximation of a 1/4 wave antenna on VHF aircraft frequencies. When the transmitting antenna is a foot or so away from the headset, it has the potential to pick up quite a bit of energy.

A 182 at a local club had one of the com radio cables connected just below the panel with a BNC barrel connector. That let folks use a short bnc-bnc cable to connect a handheld radio to the aircraft's outside antenna, which worked great when the radios in the aircraft didn't work. FWIW.
 
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