2-Way Radio Antenna

My RV-6 has a Dorne and Margolin DM C 70-1 antenna installed for the comm. radio. I'm wanting to replace as my receive reception range seems to have decreased. I'm using RG-400 coax to connect the antenna to my Dynon SV-COM-425 radio. Checking prices on the DM C 70-1, this antenna is quite expensive. Does anyone have a less expensive substitute they could recommend? Would the Rami AV-10 be an acceptable substitute?

Delta Pop's antennae have a good reputation at a reasonable price. I've been flying one on my RV-6 for many years and am very pleased with it.

http://www.deltapopaviation.com/VHF_Com_Antennas.html

It looks like the Delta Pop uses a different mounting hole pattern compared to DM C70-1A. It'd like to keep the hole pattern the same for a quicker & easier install, which is why I mentioned the Rami AV-10 (last image).

Andre,

I wondering how you decided the antenna is a problem. These antennas are dirt simple, a quarter wave element with a mount and coax connector. Unless damaged or you have a bad feed line they work.

I suggest you put an antenna analyzer on it to verify operation. If there is an antenna internal connection or a feed line problem it will show up.

Replacing a working quarter wave antenna with another quarter wave antenna will not provide better results.

Carl

As Carl said, it's far more likely the coax/connectors are causing your issues than the antenna.

Also, these antennas require a good ground connection right at or under the antenna. Check the mounting screws/nuts for any sign of corrosion between them and the airframe. (This will also show up if you can borrow the antenna analyzer Carl mentioned).

A bit of a story - last year I finished the upgrade of my panel to a Dynon HDX system, including a new SV-COM-425 radio. During my 1st cross-country flight after the upgrade, I could barely hear ATC through the static & noise I was receiving on the frequency shown on the sectional for that area. On another flight, I was using flight-following and was instructed to change to another center frequency but never got a reply when I tried checking in. I discussed all of this with my IA and we both concluded the antenna was the culprit as I'd replaced the RG-58 coax with RG-400 with the new radio install. My IA works on flight school planes and told me he sees a lot of radio antennas go bad. As my current antenna is over 20 years old, I thought it might be time for a replacement. I don't have an antenna analyzer to check it with.

Carl Froehlich said:

Andre,

I wondering how you decided the antenna is a problem. These antennas are dirt simple, a quarter wave element with a mount and coax connector. Unless damaged or you have a bad feed line they work.

I suggest you put an antenna analyzer on it to verify operation. If there is an antenna internal connection or a feed line problem it will show up.

Replacing a working quarter wave antenna with another quarter wave antenna will not provide better results.

Carl

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Interesting. Your old system worked, you put in new coax and a new radio, and now it doesn’t? IMHO that points to the radio or coax. Do I understand that the problem exists on some frequencies, but not others? That points to the radio. Many modern coms have some internal switching, where one circuit is used at the low end (say, 118.00 MHz) and a different circuit is used at the high end (say, 135 MHz). If you can compile a list of ‘good’ frequencies and ‘bad’ frequencies your local shop will know right where to look. Or if it’s still under warrantee call Dynon with this description of good/bad frequencies, they should fix it.

My problem does not appear to be frequency specific. Also, the antenna was never touched during the new equipment install but I did make sure the 4 mounting screws on the base were secure. I'll check the BNC connectors again on each end of the coax to make sure the center pins are protruding far enough out to ensure a solid connection. Would using an ohm meter across the antenna BNC connector reveal anything, other than an open antenna?

[email protected] said:

My problem does not appear to be frequency specific. Also, the antenna was never touched during the new equipment install but I did make sure the 4 mounting screws on the base were secure. I'll check the BNC connectors again on each end of the coax to make sure the center pins are protruding far enough out to ensure a solid connection. Would using an ohm meter across the antenna BNC connector reveal anything, other than an open antenna?

Click to expand...

First I would replace the RG-400 cable with the old RG-58 and check reception. Then use your ohm meter to check the RG-400 for center conductor continuity/short. Then check the center conductor to OD of the BNC for a short. Finally the one end BNC connector to the other end BNC connector to verify continuity with the shield.

Doesn't sound like the antenna to me. Previous advice to borrow an antenna analyzer applies.

terrye said:

First I would replace the RG-400 cable with the old RG-58 and check reception.

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^^^ THIS ^^^

If it fixes the problem then replace the "old" RG-400. Just checking for resistance might not expose the problem.

If it doesn't fix the issue then try a different (handheld?) radio with the coax and antenna. Final thing is to check/change the antenna.

Systematic troubleshooting will find the problem.

I was having similar issues.
I narrow down after some testing and researching that its a radio issue, you maybe in the same situation as I am.
The radio that you have was made by Dynon and they are full of issues. if you do some forum research on dynamo forum you will find it. I wrote Dynon told them the issue and they right away sent me and RMA number, no questions, no more troubleshooting. They are replacing it with their new radio built by trig (rebranded to Dynon). if you current radio is a black plastic case you have the Dynon built. If you radio has a detachable metal tray (just like the transponder) you have the newer unit.

Rico - I did contact Dynon regarding this issue and they did the same with me - issued an RMA and exchanged my comm radio with a Trig unit. Unfortunately I am having the same issue with the replacement.

RicoB said:

I was having similar issues.
I narrow down after some testing and researching that its a radio issue, you maybe in the same situation as I am.
The radio that you have was made by Dynon and they are full of issues. if you do some forum research on dynamo forum you will find it. I wrote Dynon told them the issue and they right away sent me and RMA number, no questions, no more troubleshooting. They are replacing it with their new radio built by trig (rebranded to Dynon). if you current radio is a black plastic case you have the Dynon built. If you radio has a detachable metal tray (just like the transponder) you have the newer unit.

Click to expand...