[Elecraft] KX3 Field Ant. for 80/40/30

[K9MA]

On 11/19/2017 02:22, Erik Basilier wrote:
> The second approach, used by MyAntennas and others seems to use a
> transformer with much higher impedance ratio. One way to construct such a
> transformer would be to cascade two 9:1 units for an effective ratio of
> 81:1.

While I haven't tried it, it would probably be very hard to build a pair 
of 9:1 transformers or a single 81:1 transformer with low enough stray 
capacitance to work on the higher bands.  It might work up to 40 meters, 
I suppose.

The big advantage of a resonant end-fed half wave is that very little 
current flows in the ground system or counterpoise, so most of the power 
is going into the antenna.  While it is hard to match that high 
impedance with a non-resonant transformer, it is very easy to match with 
a simple L network.  The only reason the internal ATU in the KX3, etc., 
can't match it is that it doesn't have enough range.  (And for good 
reason.)  An external L network consisting of a tapped coil and variable 
capacitor will do it nicely.

73,

Scott K9MA

-- 
Scott  K9MA

k9ma at sdellington.us