[Elecraft] Attaching a whip to the KX3, HT-style or table-top (right angle)

[Jim Brown]

On Thu,3/31/2016 6:06 AM, km4ltv at gmail.com wrote:
> When you operate mobile, do you use some sort of magnetic mount to support the whip? Also does the metal of the vehicle take the place of a counter poise?

I'm not Wayne, but I've studied this issue. Yes, the vehicle chassis 
needs to serve as the counterpoise for a mobile antenna, but I have yet 
to see a mag mount that does that effectively. VHF/UHF mag mounts are 
designed to do that by means of capacitance between the mount and the 
roof, but nearly all that I have seen have no contact between the coax 
shield and the enclosure of the mount!

At HF, I see no practical way for any mag mount I've seen to have 
anywhere near enough capacitance to a roof to work as a counterpoise at HF.

If you want to work mobile, you need to make a solid connection to the 
frame, AND it needs to be a part of the frame that is not insulated from 
the rest of the frame by PAINT. That isn't easy in most modern vehicles.

Two examples. With a Volvo S80 I owned about 15 years ago, I used a 
license plate mount for Hamsticks. The license plate holder was 
insulated from the trunk roof, and the trunk roof was insulated from the 
rest of the body by the hinges, so I had to bond around both. That 
worked pretty well, but I suspect there were still pieces of the body 
that were insulated by paint.

Second example. My current vehicle, a 2006 Toyuota Sequoia (big SUV) 
that I bought in Nov to move to CA from IL. It was winter in Chicago, so 
K9IKZ let me bring it into the loading dock of his biz, and we poked 
around to try to find good contact with the body. Lots of paint in the 
way -- I found bolts a few inches from each other with no continuity 
between them. I eventually mounted the antenna socket to the roof rack, 
and found a nearby bolt that did get to the body.

That worked pretty well as an antenna, but the vehicle has really bad 
susceptibility to HF RF -- at 100W on 20M, the main computer that runs 
the vehicle goes into "limp home mode." I've never bothered to try to 
fix it -- I was in the process of moving when I learned that (on an 
isolated stretch of I-80 in the NV desert), so didn't have time to chase 
it down, and because it was RF on the body that was exciting vehicle 
wiring, I figured that it would have been pretty difficult to fix. :) 
And my only interest in HF mobile is for long trips without the XYL, 
which I no longer take after I finished moving. I've heard that other 
big SUVs are far better in this regard.

73, Jim K9YC