You're close, Bill. The short counterpoise should go at the antenna end
of the feedline by the transformer, not at the radio. It probably won't
make much difference, though, as the outside of the coax will serve as a
counterpoise.
Depending on the design of the transformer, its inductance and stray
capacitance may have some effect. The inductance will affect the lower
frequencies, where it appears in parallel with the antenna. You can
compensate for that by making the antenna a bit longer. On the higher
bands, the stray capacitance may require the antenna to be slightly
shorter than a half wave multiple. (I hope I got that straight.) In
any case, if you can't match it, experiment with the wire length and see
if you can find one length that will work on all the bands you need.
I'd be interested in hearing the results. A single EFHW (multiple) and
transformer that can be used with an internal ATU alone on 80-10 meters
would be very attractive. (Or even up to 15 or 20 meters.)
Note that a 50:1 transformer has a turns ratio of about 7:1.
73,
Scott K9MA
On 2/11/2017 16:52, Bill Frantz wrote:
The next time I experiment with end fed antennas, I want to try a
matching transformer at the end of the antenna wire of about a 50:1
matching ratio. That way I will have an impedance in the feed line of
about 50 ohms and minimize coax loss. Now if I am connecting the
antenna directly to binding posts on the side of the KX(2/3), the loss
won't matter. But if I am using a length of RG174 for a light weight
feed line, the lower loss will be very nice.
Adding Don's recommended 0.05 wave length "counterpose" in the binding
post scenario sounds useful. With a coax feed, the coax should perform
that function.
Now, where am I all wet?
--
Scott K9MA
[email protected]
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