Hi, Norm:
Height above ground makes a big difference.
I modeled one using EZNEC and tried it at different heights. Here is what I
found:
At 130 ft. resonance is at 7.225 MHz
At 33 ft. resonance is at 7.05 Mhz.
To resonate at 7.150, the overall length was 65 instead of 66 feet. Since
the radiation resistance is about 80 ohms at this height, the SWR compared
to the 50 ohms most SWR bridges show is 1.6:1, not bad at all.
I hope this helps.
VY 73,
Bill, N5TU
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