"Jimmie D" wrote in message
...

"Ed G" wrote in message
92.196...


Our ARES station has had a NVIS antenna on the roof of the building
we are in. It is a large, one story structure with a rubber coated on
steele roof.

The dual dipole type antenna, center at 14' and ends at about 3'
high, was fed with a long run of coax and has historically exhibited a
large SWR when operating below about 3825 KHz.

We recently replaced the entire antenna assy with a 122' half wave
dipole, fed with 600 ohm ladder line to an SGC antenna coupler at the
base of the center mast. Heights are the same as previous.

The SGC 237 coupler tunes the antenna well above 3825, and all other
bands, too. However, we still exhibit a very high SWR when going below
about 3825 and the tuner fails to tune... in fact the Radio's power drops
way down, possibly preventing the tuner from working properly. A
different radio shows the same problem.


QUESTION: Can anyone offer reasons we may be having this tuning
problem below 3825?

Thanks.


Ed K7AAT


Not surprising with a dipole located that close to a counterpoise. The
feedpoint impedance should be pretty low, I would guess 10 ohms or less.

Jimmie

It occurs to me a bandaid fix might be a 4:1 balun. Just hook it up
backwards; that is the 200 Ohm side to the tuner and the 50 Ohm side to the
antenna.

Tam/WB2TT