> If your feedline changes the resonant frequency of your antenna, that is
> an indication that your ground radials are insufficient. The resonant
> frequency of a vertical or inv L will change as a function of your
> radials, if you only have a few radials. As you add more radials, the
> resonant frequency will stabilize and no longer move. Your feedline is
> acting as a long radial.
> Jerry, K4SAV
--------
While I agree with Jerry on a lot of hs points, I have to take exception
to some of them. But then, lacking the information on how long Jeff's
antenna for 160 was. ( 1/4 wave? )
Assuming it was a 1/4 Inv. L, the pure base impedance of the antenna, at
its resonant frequency, would be in the range of 35-38 ohms, depending
ENTIRELY
on the soil at Jeff's. In typical Georgia clay, or sand you might as
well take a figure
of about 13 ohms for ground loss, and this is with an 8' ground rod (
galvanized, NOT copper ) directly
below the antenna. Here's where we get the so called 1:1 SWR and
everyone is happy. Never mind that
at least 26% of your input power is being wasted heating up the ground.
I would be more comfortable with Jerry's first statement if he had said
"If your feed line changes
the "apparent" resonate frequency of your antenna, you've got a BIG
problem. This old wives tale should be put to rest once and for all.
There is absolutely NO way a change in feed line length can affect the
resonate frequency of ANY antenna. It merely shifts the reactance
between the outgoing wave and the reflected wave to
where the SWR meter is reading a cancellation of reactance because of
the phase difference between the 2 waves. Add the line AFTER the SWR
meter to the Tx, and you will see absolutely no change at all. It's
become a point of WHERE you are measuring it.
Adding radials has absolutely no effect on the resonant frequency of the
antenna. It MAY appear to do so because you are putting more power into
the antenna, and again, that dumb SWR god is being chased. In Jeff's
case, he could have as much as 20 to 30 ohms of ground loss, and adding
radials would cause a drop in
SWR because he would be approaching the pure resistance of the antenna.
Actually, assuming he put up about 60 radials, his indicated SWR would
go through 1:1 as he approached the ground loss figure of 13 ohms, and
then
begin to rise, which would be a great indication that he was making real
improvement. When he reached a point
where the SWR was at 1.35:1, he's got as good as you can get.
In summary, getting the antenna resonate FIRST is the most important,
then deal with the reactances you find.
But, in the end, Jeff's performance with this system and the score he
racked up is impressive.
BTW, Georgia soil is much too acid to use copper rods.
73
Ed
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