On 11/6/2010 9:53 AM, Bill Gillenwater wrote:
> If you have a feedpoint impedance of 32 ohms on an inverted "L" for 1.8 mhz,
> can anyone venture a guess as to what the impedance would be of the same
> antenna at 3.5 mhz ??
VERY high -- if it's 32 ohms on 160M, it's close to a quarter wave,
which would make it close to a half wave long wire on 80M. WAG about
10K ohms.
A good compromise is to make it a bit shorter (or longer) on 160, which
makes the Z not nearly so high on 80 (because the Z rises VERY fast as
the antenna hits a half wave). How much is "a bit short or long?" I'd
say 10-20%. Several years ago, I had a Tee vertical that was close to
resonant on 160, fed by about 30 ft of RG8. I could load and run full
power to it through my Ten Tec 229B on 80 CW, but not on 75M -- it was
too close to a half wave there.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|