just wanted to share

[nosaj]

I got my antenna analyzer working and during lunch decided to try an tune a 2m/70cm antenna on a mag mount. Target frequency was 146.**Censored** I could not get it below a 3 swr. Around 144 I could get it to around 1.5 swr.. I talked to my mentor and he said just make an ugly balun about 6in from the mag mount. I couldn't understand how the ugly balun(RF choke) would help. I thought it was the mag mount .I put a dummy load on the mag mount and it read 50 ohms and a 1.1 swr so that told me the mag mount was ok.

What I failed to understand was that adding the ugly balun was in this situation it was acting as inductance to lower the SWRs.

Just thought I'd share what I learned and understood on lunch break.

nosaj
N1EBC

[MDYoungblood]

Hmm,, did it work? Common mode current is a problem with some magnet mounts, even screwing a dummy load onto the mount (I guess it is a SO239 type) will only show the coax/connection is good but not that the antenna has a sufficient ground plane. Moving it around the roof sometimes yields a better stand wave, you would think the center is the most efficient but some cases I found a corner better. Chances are it is the antenna itself as the problem.

3's

Greg

[Lost Ram]

IN ROUGH LAYMAN TERMS: The ugly balun is choke, the inductance is not really doing anything. It just stops the common mode issue associated with many 2 meter antennas. These wraps of coax stop the common mode from traveling down the coax, essentially terminating the radiating antenna from the coax.

[MDYoungblood]

True, you normally don't have the problem if the antenna is permanently mounted as the coax run is inside the vehicle shielding the antenna from the effects as where a magnet mount has a coax outside where the antenna can see it and tries to use it as the ground plane, the shorter the exposed coax the higher the SWR would be. Same holds true with lower frequencies.

3's

Greg