Topband: Broadband vertical

[Earl W Cunningham]

In a previous e-mail, I stated that a Swedish ham's two-wire shunt feed
system increased his BW from 100 kHz to 110 kHz.  That was in error.

I revisited those model files and here are the corrected values:

single-wire shunt = 90 kHz  BW (2:1 SWR)

two-wire shunt = 130 kHz BW (2:1 SWR)

The increase in BW is about 44%.

SM4CAN's tower was 23m high with a 6-el 20-meter Yagi at 24m on a 15m
boom for top loading.  This structure is 1/4-wave electrically at about
1.555 MHz. (about 0.3 wave at 1.83 MHz).

For a single-wire shunt, the 50-ohm tap was at 21m.  The required
capacitor was 264 pF.

For his two-wire shunt (wires spaced 0.5m from each other), the 50-ohm
tap was at 23m (top of tower).  The required cap was 557 pF.

In both models the shunt wires were #8AWG and the shunt wire(s) was
spaced about 0.5m from the tower.

I apologize for my error in remembering incorrectly that there was an
insignificant difference in BW between a single-wire and multiple-wire
shunt feed.

73, de Earl, K6SE