[Elecraft] Efficiency of MFJ remotely-tuned loop antennas

[Augie "Gus" Hansen]

On 1/19/2021 8:20 PM, Andy Durbin wrote:
> A couple of people expressed an interest so here is a link to a presentation on my mag loop.   It's a while since the presentation was given but the loop is still in service in the gamma match configuration.
>
> https://www.dropbox.com/s/5va4ygzbd410le4/Prototype%20Magnetic%20Loop%20rev%20-.pdf?dl=0

Nice job Andy. Looks like we've both had some fun with these antennas 
that have become quite popular in recent years.

My interest in Mag Loop antennas started back in the early 1980s, and I 
have designed and built a couple of dozen over the years since, mostly 
as experiments to gain knowledge and experience, and several to help 
friends who lived under extreme antenna restrictions.

The two pictures in this Dropbox folder show one incarnation of a mag 
loop that uses flat mill stock for the main loop, and a trombone-style 
capacitor for tuning:

https://www.dropbox.com/sh/gqbzz60bcwkc54h/AACAjWK6JFfyLN9qcvq9oSrqa?dl=0

My capacitor design uses PEXX tubing for the dielectric layer (must be 
protected from UV), and has fiberglass stiffeners inside the sliding 
part. The PEXX allowed me to run up to about 300 watts. And the 
stiffeners hold the tubes in line at the low capacity end of travel to 
prevent misalignment (sloppy tuning).

I long ago moved to all copper loops and vacuum variables to handle high 
power and obtain better efficiency. An example of a two-turn version of 
a 40-80m mag loop is on my QRZ.com page:

     https://www.qrz.com/db/KB0YH

It uses 7/8" Heliax (the shield) as the main loop conductor. Kinda 
heavy, so some of my newer mag loops use 1/2" Heliax or soft copper 
tubing instead. Performance suffers a little, but no one notices the 
difference.

Have fun and keep safe.

Gus Hansen
KB0YH