It occured to me that Jim, N7US may not be able to shunt feed his tower
at a specific height above ground because it is a crank-up tower (and the
tower may not be able to be fully telescoped due to interference by the
shunt wire attachment). Unless the 50-ohm "sweet spot" is at (or near)
the top of one of the tower sections, an omega match may be the answer.
An omega match will work well in this case, where he can attach the shunt
wire to the top of the first or second tower section (but not too high!).
Tuning the omega capacitor has the same effect as moving the shunt wire
up higher the tower. The gamma capacitor does the same as in the
single-capacitor method - it tunes out the inductive ractance at the
feedpoint.
73, de Earl, K6SE
|