Topband: Hairpin Matching Coil Questions

[bills stuff]

To amplify a little on some other comments -  For an Inv L, and a decent 
radial system, with a coil shorted across (shunt) the vertical wire 
input to the braid/radials, the otherwise low impedance can be 
transformed to 50 ohms.  One way to do it is to use an antenna analyzer 
to measure the unmatched impedance and then adjust the length of the 
horizonal-ish leg to get the reactive component to be roughly -20 ohms 
(capacitive, and the resonance with be ~ 1.9 MHz for a 1.825 target) and 
the resistive component well less than 50.

Using the measured resistive component (which changes slowly with 
frequency) you can find what reactance you really need in the unmatched 
antenna for a perfect hairpin match with available calculators or from 
that Hairpin matching article in Jun QST.  Once the length is fine 
adjusted to get the needed reactance, the needed coil impedance (and 
inductance) can then be calculated or found from a graph.  Then wind 
your coil long and find the tap (or stretch) that minimizes SWR at your 
favorite frequency.  A bit more back and forth may be required.  No need 
for beauty and the coil is not huge.

 From multiple personal experiences, this can certainly be done, 
although beware that a NEC model to get initial antenna dimensions may 
be far enough from reality (dimensions way too long in one case and long 
in others).  This may be particularly painful if no antenna analyzer is 
available.  Some experiences recounted on my webpage and a calculator is 
there.

Bill N6MW