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

[Bob McGraw K4TAX]

For that very reason, in our camper operation, I use a end fed antenna.  
The matching network is a tapped coil and variable C forming an L 
network.  The circuit is in a small plastic box with a SO-239 on each 
end, thus it is reversible.   This allows a wide range of impedance 
selections, plus the L network, unlike a T network, will only resolve a 
match at one value combination of L and C values.

I carry a 100 ft spool of #22 insulated hook up wire.  Unroll some 
estimated length, drop a half hitch around the spool and toss the spool 
over a convenient limb.   When ready to retrieve the antenna, turn the 
feed end loose and let the spool drop to the ground.  I've never 
experienced a length or condition where I could not satisfactorily match 
the band/frequency I wanted to use.

73

Bob, K4TAX


On 11/19/2017 10:26 PM, K9MA wrote:
> 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
>