COMM Antenna tuning

[Martin S.]

Evening gents,

question regarding COMM antennas. Can somebody tell whether the stock "7-type" antennas are "tunable". It seems mine are not. Let´s presume I was conducting a VSWR test and was unhappy with the result, how could I change it - other than by swapping the antenna or replacing the wire?

Greets,

Martin

[EricJ]

They are not tunable.   VSWR isn't a very good test of an antenna, and about the only thing servicable is to make sure the base and connector are clean and free of corrosion.   Are you testing at the antenna or is the cable included in your testing?   Cables are more prone to deterioration and problems and are easier and less expensive to swap out.

 

[Fly Boomer]

16 minutes ago, Martin S. said:

Evening gents,

question regarding COMM antennas. Can somebody tell whether the stock "7-type" antennas are "tunable". It seems mine are not. Let´s presume I was conducting a VSWR test and was unhappy with the result, how could I change it - other than by swapping the antenna or replacing the wire?

Greets,

Martin

Pursuant to Eric's comment above, the prevailing wisdom these days is to use RG400 for all the coax.

[N201MKTurbo]

I did a lot of work with the 7 antennas. Mine weren't working very well. At one point I had 4 of the 7 antennas. I tried all four of them in both locations. All the antennas performed the same. they all worked better in the rear location then the front location. I was using an MFJ antenna tester, which is just a variable frequency impedance bridge.

The best VSWR in the rear position was about 1.3:1 the best at the front location was about 1.5:1. The center frequencies were position dependant, but they tended to be about 2/3 from the bottom of the com band to the top of it.

When I started the front antenna was horrible. I removed it and all the mounting hardware was rusty and there was a lot of rust in the vicinity of the antenna. The front antenna mounts to the steel cage. you have to disassemble the air plenum to get to the antenna mount. After I cleaned up all the rust and repainted the tubes, I assembled the antenna with new SS hardware and put star washers under the nuts so there would be a good ground. then the antenna performed properly.

The rear antenna is mounted to the aluminum and seems to perform better. I put my #1 com on the rear antenna.