In a message dated 11/6/02 4:52:47 PM Pacific Standard Time,
tmartin@chartermi.net writes:
> I built a 15 meter beam with the DE cut for 21.250. The MFJ analyzer
> reads 23.000 for a 1-1 match. I added about 8 inches and the best SWR
> is at 22.500. These tests were made at 10 feet. Will the frequency go
> down when the beam is at 40 feet? I can't believe that I have to keep
> adding to the DE.
Typically the added ground capacitance lowers the frequency of antennas
close to the ground. A typical 40M antenna might resonate at 6.700 on the
ground and be fine in the air. Mostly the same effect for other bands.
Try pointing the antenna vertical with the reflector resting on the
ground and take another reading. This will give you a better idea of the
resonance but still not like having it in the air.
Did you run a taper program for the elements?
Cheers,
Steve K7LXC
TOWER TECH
|