> I slapped together an 80m dipole using the L=468/F formula
and find that it resonates about 200 KHz lower than
expected.
>
> My target frequency was 3.775 MHz. That's 124 feet on my
calculator.
Hi Bob,
We cannot measure resonant frequency in the shack unless
resonance happens to occur with the same resistance as the
feedline.
In other words if your dipole had 75 ohm pure resistance at
resonance, the point where you measured 75 J0 would be the
same at the analyzer end of the cable as at the antenna.
If you cut the cable to a multiple of 1/4 wl you can still
be misled because it is only 1/4 wave or a multiple thereof
at one frequency. (Any cable a multiple of 1/4w long would
be J zero at the analyzer end when it was J zero at the
antenna end regardless of SWR on the line.)
If the line has standing waves you have to either normalize
the line out of the picture (network analyzers do that, your
antenna analyzer cannot) or do a lot of trimming and
testing.
73 Tom
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