[Antennas] Re: mobile antenna matching coil

[Roy]

Concerning,

"Some years ago, QST had a piece on how a simple coil

mounted between "hot" and ground at the base of a

mobile antenna would act to match the low Z of the

mobile antenna to 50 ohms.

I can't locate the articla and would be grateful for

any assistance.  I've got a 6 1/2 foot mast with a

homebrew coil/whip that reaonates fine but has @20

ohms of R rad.  This for 10 meters."

73,  Tim


Tim,

This has been referred to as a "Z-match" or "inductive match" over the 
years.  It's the same thing as a 'hair-pin' match used in a yagi antenna.

All you do is install a small inductor from the bottom of the whip to 
ground. It has been referred to as a shunt coil because it's in parallel 
with or shunting the feedpoint, across the coax. For 10 meters the coil will 
be small indeed, maybe two turns, air wound, one inch in diameter as a 
ballpark starting point. Adding the shunt coil will slightly lower the 
resonance of the antenna, so you must juggle between re-tuning for resonance 
with the main loading coil, and minimum (1 to 1) swr at your preferred 
operating frequency with the shunt coil size.

Luck and 73,

Roy   K6XK     Iowa