[Elecraft] EFHW

[K9MA]

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

k9ma at sdellington.us