[Elecraft] OT: Mobile operation "bible"

[Myron Schaffer]

All, 

The coax length doesn't matter because of the following reasons. Assuming the tuner is at the rig, there is a run of any coax to the antenna feed point, and you have a fairly high Q low band antenna that can't QSY much. 

With short HF mobile antennas that are high Q the reactance at the feed point when you QSY beyond 3:1 or so makes the system very lossy regardless of how low a loss or how short of coax is in there. 

The power accepted by the antenna under these conditions goes down the further you QSY due to the large reactance leaving the dissipated power to be burned up in the coax (and some in the imperfect antenna tuner at the rig) no matter how low loss it is or how short it is. You cannot increase the power accepted by the antenna unless you bring the feed point back closer to 50-ohms somehow through external loading of the antenna. (Even then there are other loss factors to consider such as ground loss and radiation resistance).

It's kind of like a "tug of war" between two Qs. The antenna Q and the tuner Q with the coax in the middle accepting all the power.

73/72,
Myron WVØH
Printed on Recycled Data

> On Mar 31, 2016, at 11:09 PM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> Bearing in mind that in a mobile installation, coax is too short to introduce enough loss to matter, so it's merely a matter of making the rig's output stage happy (and running at full output).