Topband: Inverted-L

Guy Olinger, K2AV olinger at
Sun Mar 5 09:38:18 EST 2006

George (K8GG) wrote:

"Keeping the 160 meter inverted-L connected to ground through the 
prevents it from being a resonant half wave floating wire on 80 when 
the 80 meter vertical nearby"

Whether the connection would appear as a ground would depend on the 
winding used and the coax connection. It would be possible for a 
combination of a length of coax and the winding used to appear as a 
parallel resonant circuit on 80m, putting the antenna in play as a 
parasitic element.

Check whether the coax/winding combo "grounds" the antenna by checking 
with an analyzer looking at the shack through everything, with that 
antenna NOT selected at the antenna switch. Particularly if the Z is 
very low, it could still be subject to the voltage issues raised 
earlier by W8JI at the other end of the coax. Would be at its worst if 
the electrical length to the switch is an odd multiple of a quarter 
wave on 80m.

Even without that, the Z measured by the analyzer should be put in a 
model containing the two. Place the measured Z in a load at the base 
of the inverted-L and run it. Interactions seem to mostly be worse 
than thought.

Positive relay action at the feed point to short to ground is still 

73, Guy.

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