[Antennas] Butternut HF-6V Antenna

[Ray Brown]

----- Original Message ----- 
From: "David C. Hallam" <dhallam at knology.net>


>I am having a problem with my Butternut HF-6V vertical antenna.  After a 
> year or so of geed service, the 20M VSWR suddenly increased to 2:1 and 
> nothing I have been able to do has moved it back down.  Adjusting the 
> tap position on the coil has no effect.  I don't have an antenna 
> analyzer and am out of ideas.

  Well, you really need an analyzer. But let's try a few things.

  First off, did your SWR change on any other band at all?
Second, did you re-read the theory of operation starting on page 8?
It discusses in great detail how it works, and how 20M is always a
little problematic. I'll go ahead and quote the section on 20M:

  "On 20 meters, the entire radiator operates as a 3/8 [wave] vertical,
with much higher radiation resistance, and VSWR bandwidth, than 
conventional or trapped antennas having a physical height of 1/4 [wave]
or less. Because the 20 meter radiation resistance will be several times
as greater as that of conventional vertical antennas, an electrical 1/4 
[wave] section of 75-ohm coax is used as a geometric mean transformer
to match the 100-odd [level] of feedpoint impedance on that band to a 50 
[ohm] main transmission line of any convenient length."

  So... another thing to check - did you alter or replace the matching 75-ohm
coax that immediately attaches to the coil at the bottom of the antenna?


                Ray, KB0STN
                (owns 1 at home and takes care of 1 at work :-)