Topband: Good or bad conductivity
RadioIR at charter.net
Sun Apr 26 08:12:24 PDT 2009
allan1 dejazzd.com wrote:
> I've got all the materials for an 160/80 EWE including a commercial 3:1 matching xmfr with pre-amp which I am thinking of installing. My soil is red clay. Will this soil's conductivity make for a good rcvg ant or a poor one? ........
Here in Alabama we have real red clay. It turns to slippery goo when it
gets saturated with water, and turns to pottery in the summer. Even
though it has a lot of iron content, it isn't very conductive (at least
near the surface). An EWE will work fine, but I would recommend an
eight ft ground rod at each end. I tried four ft ones and it worked OK
with a 4 element EWE (two element used at a time), but it worked better
when I changed to eight ft ones.
When you analyze this you will find that a very good ground is not
needed for the EWE, however a 4 element version is a lot pickier than a
two element one, and is dependent on both elements being matched. A
poor ground (greater than about 200 ohms) makes that more difficult. A
poor ground usually results in some loss of forward gain and some loss
of front-to-back. With a single element EWE you can juggle the
termination resistor and get that F/B back even with a poor ground but
things are difficult to control with a poor ground. Each direction may
be different, small changes like rain may make a difference, and the
effect is different at different frequencies. So if you have a ground
that is 100 ohms or less, things are a lot more controllable.
A three to 1 transformer isn't a very good match for the feedpoint
impedance of the EWE. Normally for 50 ohm lines you need about a 12
to1, and for 75 ohm lines you need about 8 or 9 to 1. However with a
transformer/preamp it may work OK if it has enough gain and it is
located at the EWE. Also the preamp needs to have very good intermod
characteristics. Local AM stations put out some pretty strong signals
and short wave broadcasts stations can be a problem too because the gain
of the loop increases by maybe 25 dB for those stations.
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