Homemade antenna

Discussion in 'Instruments / Avionics / Electrical System' started by Dana, Oct 8, 2007.

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  1. Oct 8, 2007 #1

    Dana

    Dana

    Dana

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    I have an Icom A24 radio which transmits a horrible squeal when used with an external mike (my Comtronics helmet). Apparently I'm not the only one with this problem, and I'm experimenting with shielding etc. (advice welcome), but it may well be that the only real solution is an external antenna, far from the mike.

    Anyway, I know an antenna is a relatively simple thing to make, but I don't know too much about the specifics... any pointers to homemade antenna info would be appreciated. This is to mount on my Kolb Ultrastar, so the mounting and ground plane have to be able to coexist with the fact that I fold/unfold the wings every time I fly it.

    -Dana

    Refuse Novocain... Transcend Dental Medication.
     
  2. Oct 8, 2007 #2

    Yet^Another^Dreamer

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  3. Oct 9, 2007 #3

    Dana

    Dana

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    Thanks, that's just the kind of information I was looking for. I had seen references to the kitplanes articles but not the actual articles until now.

    Turns out a couple of ferrite beads (from a computer monitor) reduce both the frequency and volume of the squeal, but don't eliminate it. Grabbing the antenna with my hand eliminates it, as does (this is weird) looping the headset cord around the antenna. Don't know what that does to the transmitted signal strength, though.

    -Dana

    How is it that 2 teenagers in the back of an original Volkswagen Beetle, in a crowded drive-in theater, can reproduce, yet it takes 2 spotted owls 10,000 acres?
     
  4. Oct 10, 2007 #4

    Midniteoyl

    Midniteoyl

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    The squeal is usually feedback from RF signals getting back into the system, being demodulated, then amplified, then put back into the radio - creating a feedback loop. Look for cabling problems. You may have put extra-long headset leads on the system (antenna), or run the radio interface lead close to the antenna. You may even have put the radio itself right next to the intercom. The problem can also occur on some systems if there is a problem with poor power contacts or grounding.
     
  5. Oct 10, 2007 #5

    Dana

    Dana

    Dana

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    Yes, the squeal is definitely RF feedback. The cabling (not installed on the plane yet) is all shielded, though I don't know if the actual helmet cable is shielded. Strangely, if I actually loop the helmet cable around the antenna the squeal goes away... though that's hardly a solution. Yesterday I wrapped a coil of the helmet wire around a mechanical pencil, and it nearly elimitated the noise... completely elimininated it if I stretched everything way out. I think that's the ticket; if I can scrounge up a ferrite core from an old AM radio to wrap the coil around it should be even more effective, and the cord is too long anyway.

    This is looking better; I'd really prefer to use the built in rubber duck antenna since there's not really a good place to mount an antenna on my plane, unless it had been planned before the wings were covered (I bought it used and flying).

    -Dana

    But do you trust the _government_ with semi-automatic assault rifles?
     
  6. Oct 10, 2007 #6

    Greg Mueller

    Greg Mueller

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    This might sound a bit strange....
    The best book I ever read on antennas was back in the CB radio days. It was called "The Truth About CB Antennas" by William Orr. Lots of good information at the entry level and had several antennas you could build yourself. These were all for the CB freqs, but once you understand how it works (which it explains) it's easy to translate to other freqs.
     
  7. Oct 11, 2007 #7

    Midniteoyl

    Midniteoyl

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    "My 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."
     
  8. Oct 17, 2007 #8

    Rhino

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    http://www.arrl.org/catalog/?item=9876

    It's meant for hams, but the aviation band also falls into areas of the ham radio spectrum. It's extremely complete.

    I also recommend http://forums.matronics.com/.
     
  9. Oct 17, 2007 #9

    Dana

    Dana

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    Update, no combination of ferrite beads, chokes, capacitors to ground, etc., fixed the problem... but remoting the antenna even 2' away from the radio did. Accordingly, armed with an RG58 cable from Radio Shack and a homemade clamp to mount the original rubber duck antenna under the floorboard, I'm all set... though it'll take a weekend flying with my friends to see just how well it puts out.

    -Dana

    This is a test of the emergency tagline system. Were this an actual tagline, you would see amusing mottos, disclaimers, a zillion net addresses, or edifying philisophical statements. This is only a test.
     

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