A silk purse from a sow's ear?

[geoffreywh]

I found this lovely piece of information on an American website that deals with aviation radio problems. They are answering questions about Icom A-6 and A24 radios in ultralights and trikes

 

 

 

A6 or A24 radio squeals when I transmit!

 

Miniaturisation of handheld radio transceivers reached a new level with the intriduction of the A6 and A24 radios. Unfortunately, to miniaturise the radio Icom also had to miniaturise the batteries, and to get enough battery life, they had to go to a 7.2 volt battery pack. The problem is, most GA headsets are designed to expect about 9 volts available from the radio, and without this voltage, many do not work well, and a side result is usually that RF energy from the radio antenna gets into the mike circuit, causing a squeal. Icom know about the problem, but there is no fix except fitting a remote antenna and getting it as far away from the headset and leads as possible.

 

We do NOT recommend this transceiver for use with a headset.

 

Isn't that nice to read after the guy in the shop assured me that I can use the A6 in a cockpit and even sold me an intercom to connect to it..none of which work at all well....Geoff

 

 

[BigPete]

Use your consumer rights and return the not suitable merchandise.

 

regards

 

 

[ZULU1]

ICA6/24

 

Hiya again

 

I discovered this about three years ago. I have just posted the fix on the same forum. Yes the problem is rf getting into the mic circuit. Not an expensive fix. I will do a drawing and post later. The 5 volt supply from the radio has to be decoupled with a 100nf capacitor and then a seperate supply fed to the mic element. Normally popping a 1,5 volt AA battery in the headset works. For good measure a 470pf 0805 smd cap across the mic and the rf bead from the charger around the cable. I hate that radio..

 

The very same circuit is used in Military HF radios as they have similar problems with them.

 

Paul

 

 

[geoffreywh]

yes, well !

 

I know you are writing english as I recognise some of the words! Otherwise I have no idea what you are talking about, I thought, for a start, that the radio uses 7v olt?...thanks Geoff

 

 

[sain]

the 100n capacitor that Zulu1s talking about simply blocks D.C voltage travelling between the microphone element and the radio, but will still allow the AC audio signal to travel. This means you can add a seperate power supply (the AA battery) to power up the microphone and eliminate all the nasty squeal you've been getting, without frying the audio input circuitry in the radio. The other bit with the ferrite bead and other capacitor is to elimnate noise being induced on the line...

 

The radio itself makes use of 7v, but only 5 on the microphone line (i'm guessing here, based on what zulu1 has said - I don't actually know and can't be stuffed looking it up).

 

The good news is that Zulu1s fixes will only cost a few dollars and should solve the problem.

 

 

[ZULU1]

Correct Sain

 

I am sorry chaps and should have described it better !! The power from the radio is about 4,8volts (seen some higher as well). The objective is to keep the mic voltage as low as possible, most electret mics are about 1,5volts or so. If using a mic amp it makes the clarity from the headsets about 100% better as the battery power is "pure".

 

The mic elements are good, its how they are connected..

 

I have used this circuit in very troublesome hf systems, they are prone to rf ingress and in every case work well. The ICA6/24 series is my first encounter with aviation radio and this challenge...Seen many web sites describing the ICA6/24 as unsuitable, unfortunately people find out after they have been purchased. That is the benefit of a forum like this..

 

Hope this helps

 

Paul

 

 

[vk3auu]

I had another problem with an Icom hand held airband radio. I was attempting to use it with the cigarette lighter plugged power adapter attached in place of the battery pack. The radio was mounted on a bracked in front of me on the panel.

 

The problem was that the radio would not mute. The problem was that the switch mode power supply in the adapter was putting out a lot of radio interference on the air band. (They are OK when attached to CB UHF sets). The cure was to discard the rubber duckey antenna which was directly attached to the set and replace it with a standard quarter wave ground plane antenna located toward the rear of the fuselage, away from the noisy power adapter.

 

David

 

 

[geoffreywh]

hold my handheld , tightly

 

Yes I can see that hand helds CAN be made to work. I wonder if it's worth the bother. Probably hand helds should be just that:- handheld, on the ground.....I am so disappointed with the guy at Moorabbin SKYSHOP. He sold me the radio knowing about the feedback problems as he gave me a ferrite clip to put around the headset cables. Didn't work though. Only my D/C headset works, but I have been told I'm still not transmitting. (receiving is just fine, ) It looks like if you use the headset cable on the A-6 then you HAVE to use a remote PTT button as well?. I read somewhere to turn the sidetone to zero...Geoff.

 

 

[ZULU1]

Power supply for ICA6/24

 

Geoffrey, I think I mentioned it on the forum before but anyway, to make matters worse the ICA6/24 series requires a 11volt supply to power direct from a plane (or car).

 

They will receive but not transmit if over 11,4 volts. The new ICA14 is the same. Minimum power required is 1,6 amps for stable transmissions. Use a minimum of a LM350 regulator as a LM317 dies at 1,5 amps.

 

Not a bad thing as the previous ICA5 and also the ICA3 would destroy itself if surged on over voltage.

 

Also ensure the ANL is on, and if possible install a line choke. Most chaps use a seperate battery which is first prize.

 

The Vertex (all models) works up to 15 volts and is ideal at 9,6 volts as this gives a nice differential on a regulator such as a LM317/338/350 series from 13,8 volts which helps remove the line noise. The Tx is about 0,9 amps at 1,5watts.

 

Google the regulator types for more info, stay with a TO220 package and small heat sink as they are not 100% duty cycle. Parts are really cheap.

 

Attach jpeg of circuit diagram for you. Line choke from a speed and sound shop.

 

Safe flying

 

Paul

 

 

 

[ZULU1]

Clear Prop stocks them..

 

I am pleased to advise that the online store, Clear prop will now be stocking most fixes for "Electrical Storms" described above as well as our other Air Magic branded products. Ian has negotiated to supply at the lowest possible prices anywhere..:thumb_up:

 

The store will be stocking the Vee rabbit antennas almost immediately, which fixes almost all known woes from the Garmin GPS 296 on trikes. They are mounted on the King Post and also aid well known panel mount radio problems.

 

We have also developed a Twin comm radio intercom system allowing a Air Band and the Australian UHF CB band to operate on the same system. Two PTT buttons. Clear Prop will be the first to receive these products.

 

Also to be made available will be flying shoes, leather "biggles" helmets, visors, bibs, power supplies, line chokes, intercoms that "fix" panel mount radios, flying suits, chill cheaters (neck sleeves) trikers map boards and hopefully we can be competitive on our ally wheel chocks.

 

Contact Ian for further details, and with our closer relationships we will now "try" to help out with those radio installations on the forum...

 

Air Magic is desiged and manufacturd in South Africa and Australia for the harsh conditions we encounter.

 

Cheers Paul (zulu1)

 

 

[newairly]

Hi ZULU1,

 

Could you post the circuit diagram for the mic connection as well. It would make it much easier to understand than just a description.

 

The Icom IC A20 has the same microphone and PTT setup and the same feedback problem.

 

Phil

 

 

[jeffcb52]

I am also trying to attach a headset to an Icom A20 in order to have it as a back up.

 

Activating the PTT switch on the plug setup I made will generate a reply from the aerodrome response unit (or whatever it is called), but speech is not transmitted and is accompanied by a squeal. I have been told it is only transmitting a carrier wave.

 

I have tried installing a capacitor and resistor as per some diagrams off the net, but to no avail. I purchased a PTT setup for an Icom A20 from Aircraft Spruce, but it has no plug for the headset mic lead. Very useful.

 

I would be delighted if someone could draw a laymans diagram on how to remove the squeal and allow speech through the heaset mic. I can solder and do have a selection of capacitors and resistors.

 

Regards

 

Jeff

 

 

[geoffreywh]

what is the address for the seller you mentioned? I can't find it at all....thanks, Geoff

 

 

[newairly]

Jeff,

 

If you use a headset connection intended for a late model Icom on a A20 you will get just a carrier with no modulation because the A20 combines the PTT and mic in one connection. The PTT switch in this connection will just short out the mic input. The later models apparently have them on separate connections on the 2 circuit connector.

 

If you have a dynamic mic the PTT can just be in series with the mic because it is the partial grounding of the mic circuit which causes transmission on the A20. With an electret mic it appears necessary to separate the mic audio from the PTT operation. Hence the capacitor. It is also necessary to supply voltage to power the electret. The A20 has +5volts on the other circuit on the plug which can be used.

 

 

[geoffreywh]

voltage via Zulu 1

 

With reference to the wiring diagram posted by Zulu 1....The bloke that is making it for me just rang and said that "if the input voltage drops below 12.5 volts then the output will be zero.!!" So if your battery is a little down and your engine stops (or the alternator fails) then you cannot transmit! This is NOT a good thing..I would love to hear that he is incorrect?...... I am ready to chuck the whole project in a draw and buy Xcom..any comments would be welcome...Geoffrey...

 

 

[sain]

Short answer is yes he is right (I think), but wont the radio switch to its own battery pack when the external supply is removed (i.e giving you some more talk time)? Easiest way to tell would be to plug a power adaptor into the radio but don't hook it up to any power, and then seeing if you can still talk.

 

Long answer:

 

The dropout on the lm338 based mainly on the difference between the input and output voltages, and the amount of current being drawn by the load (radio).

 

Ideally you want the input and output voltages difference to be about 2.5 - 3 volts (assuming a 3A load - you can get away with a bit lower for a smaller load) - which in normal conditions wont be a problem for this circuit. More than that and you have to problems with excess heat needing to be dissapated, and less than that and the regulator wont function. What its going to come down to is how much current your radio draws (i don't know i'm afraid).

 

Datasheet for the lm338 is here if your interested http://www.national.com/ds.cgi/LM/LM138.pdf

 

The circuit supplied by Zulu1 wont fix all your problems with noise etc, but will supply a good, clean source of power in normal circumstances, which gives the radio a better chance of working right. If the alternator fails, you should still have the radios battery, which is a much better situation than you'd be in with a fixed radio.

 

I'd follow his suggestions for RF noise elimination on the mic lines as well - thats probably your other "big" source of noise. I'll see if I can get my hands on a spare headset to pull apart so I can do up a set of how-to instructions - unfortunately my free cash is going on other projects, so my hopes arn't high. Failing that you'll need to rely on Zulu1 (sorry Paul :-p)

 

 

[Guest airsick]

Why would you put up with something that will likely fail when you need it most? Buy the XCom and return the handheld. As BigPete said, it is unfit for purpose so you should have no problems returning it.

 

 

[geoffreywh]

Thanks for the input, No, if the radio 11v supply fails it will not fall back on the battery supply. I agree it should. It's all very difficult, especially as the power supply guys requires $250 plus for the item..I paid 750 for the A-6 plus leads and intercom, So, already a gorilla down the tubes..What an idiot, By trying to save you lose? I seem to have heard that before.. Be warned everybody.....The short way is not always the quickest way.....Geoff

 

 

[wanabigaplane]

voltage regulators

 

Using a voltage regulator to supply a smooth voltage brings its own problems.

 

Integrated circuit voltage regulators like the LM 317, LM 7812, etc requres up to 2.4 volts to work. So, if your battery charging circuit supplies 13.8 volts, you are left with 11.4 volts, which is just on the margin for some radios, but not others. You have to check the specifications that come with the radio. There are 'low dropout' regulators available.

 

These regulators also limit the current according to the temperature - on an average heatsink, it could be around 1.5 amps, which is also on the margin for some radios.

 

The squealing is due to RF getting back into the headset. I was able to reduce it on my A20 by adding a small bypass capacitor and adding a few clip on inductors, but I was never really satisfied with it. The next obvious step was to move the antenna farther away from the pilot, but I never got that far.

 

Jack. :):)

 

 

[geoffreywh]

don't worry about a thing!

 

every thing is going to be alright!................I have decided that it's all too much buggering around to get a mediocre system at best... I have done what I should have done in the first place. that is bought a dedicated aviation inbuilt radio. ....Micro air..as that is what I have done all my training with.Should arrive in an hour or so...Just goes to show that the cheapest way is not always the cheapest way!...I have learned much from the exercise!..You just have to be CERTAIN that the radio is working properly..I never got past just HOPING that it was operating correctly. The radio itself (A-6) worked fine , it's just that I was asking it to be something it was never meant to be....Thank you all for your help and assistance....Geoffrey

 

 

[sain]

Good choice in the end I think Geoff.

 

You can still use the power supply to run some other device - you can set the voltage output on the LM338 to whatever you want (as long as its approx 2.5volts below the supply)...

 

I was initially horrified at how much he was charging you for the power supply until I stopped to think about it and came up with 2hrs labour + parts + gst coming out at remarkably close to the $250. And I think it'd take me longer than 2hrs to build it (including making pcb etc).

 

 

[Guest aircraft1]

? 2 ptt's - why ?

 

We have also developed a Twin comm radio intercom system allowing a Air Band and the Australian UHF CB band to operate on the same system. Two PTT buttons.

 

? These have been around forever, i have 3 radios in my plane, two VHF and a UHF running through an xcom intercom. I only have one PTT which makes it easy and all i do is select from a 3 position switch on the panel which radio i want to transmit on. The first VHF is a panel mount, the second is a handheld which is a temporary instal and can be removed in 30 seconds if needed and used as a handheld. Very flexible setup and only one ptt button

 

 

[ZULU1]

Twin Comm

 

We make the twin comm for trikes and not fixed wings, ultra small technology. With a trike its not so easy to interchange radio transmit. hence two PTT buttons on the bar !!

 

Paul