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Comant troubles

P

PH-SCP

Well Known Member
Hi,

I bought a used Comant CI-122 antenna intended to connect to a second radio (8.33 requirements in Europe).
Although this antenna is made for an "under-the-belly" installation, I want to use it on top of the fuselage (is this at all possible ??)

Before installing, I hooked up the antenna to a coax (to simulate aircraft installation) and a handheld radio. Called the tower from 1.5NM away and they did not read me. Changing to the small whip antenna on the handheld cured the problem, "reading you five"...
Measured the coax and there is nothing wrong with it, I even hooked up the coax to an existing antenna installed in my house (for VHF RX/TX) through a double BNC-connector and readability was "five" again.... This leads me to believe that the Comant CI-122 is U/S.

How can I make sure the CI-122 is working properly ?
Your tips and tricks are most welcome !
 
Did you mount the antenna to a ground plane before you tried to use it?

There is a test device called a VSWR meter. Contact a local "ham radio" person near by and have the antenna/ ground plane tested. Or a radio shop,will have the tester.
 
Hi Simon,

Yes it will work on the top...just not as well as on the belly nor technically as well as a straight whip.

In order to do a good test with a whip antenna, it's very difficult to do accurately with a handheld..because they antenna should have a sufficient ground plane on it to work correctly.

As mentioned, if you can find a SWR meter, you can plug it in and see if the antenna itself is ok.

Hope that helps!

Cheers,
Stein
 
I second the question about the ground plane.

I had a radio problem and I tried all sorts of tests to narrow down why I could receive pretty well but no one could hear my transmit more than a couple of hundred feet.

IT turned out the antenna had lost a good connection for the ground plane.
 
The ground plane actually substitutes for the "missing" half of a half wave dipole. Expect poor performance without it.
 
Comant antennas

Very little can go wrong with a Comant. They are sealed up tight and well made. If it does not have any corrosion... mount it (grounded well to airframe) and use it. As mentioned.. you can insert a reflected power meter in line between the radio and antenna to compare power going out to power being reflected back down the coax. This is actually good practice for any radio xmit installation in a plane. The meters themselves are inexpensive... since the frequencies are pretty low.
Check ebay.... vswr meter (with BNC connectors) or you will need adapters.
 
+1 on finding a local ham radio guy. The A/C band is 108-137 MHz, just below the popular 2m ham band at 144 MHz. I have a small, cheap power/swr meter I use for quality checking antenna connections. This plus a small 50 ohm dummy load will serve you well to find the problem. Sounds like a connection problem somewhere. Depending on the type of connector, you might find an occasional "open" (contact that don't actually make contact) that will mess you up. Usually an issue with cheaper, crimp-on type connectors.

Any ham worth his salt will consider it his obligation and privilege to find the issue; you just might need to reciprocate with a flight at a later date. And, you've made a new friend!. Look for the houses with the big, weird-looking antennas on them.

Tell 'em KO6CD sent ya (I'll send them a QSL)

73,

-Bill
 
I just went thru this drill with my T-18.
All above posts apply. I had poor transmit, so during the condition inspection, I dove into the tail cone, and with the help of my brother the ham radio guy, we removed the antenna and cleaned the fuselage and antenna mating surfaces.
We tested the antenna, which went poorly, including a SWR reading.
I then grabbed a scrap piece of aluminum, about 8" x 20" and held it up to the antenna bottom....Improved SWR!
The re-installed antenna works fine now, I used conducting anti-seize, hopefully it will last a while...
I'm eliminating problems one at a time. A previous 'radio problem' was a defective magneto. The magneto static was so powerful at times that the radio auto squelch was on. When it wasn't dead from full squelch, the static blast was intolerable.
Now I have Push to talk switch static, and the flip flop switch in the Narco Com radio is suspect.
All of these problems at the same time was confusing. finding them individually and fixing them is a challenge. I missed one, and changed out the SIG intercom, to a David Clark for no more benefit than a neater installation.
So it goes with radios...:rolleyes:
So I finally got my ham ticket; KG7JRJ
 
Thanks

Thank you all very much for the supplied information.
I guess my Comant is working fine, it just needs an airplane beneath it.

I will let you know how the installation works, once finished and also, I will test it with an VSWR meter before closing the plane up...

Thanks again, just love this forum ! :) :)
Wishing everybody a very merry Christmas and a wonderful 2015 with many safe flying hours.
 
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