Hi Brian,
I did some antenna modeling work on this a while back. The Cushcraft model
40-2CD inductors are just that, inductors and not traps. I believe the
inductance is approximately 11.5 microhenry with some stray capacitance
that makes an approximate trap at 19 MHZ (that is not a typo). Hence the
performance is acceptable on 17 Meters!
If my antenna model is correct, just delete the top hats and shorten the
outer 1/2" diameter tubings so they protrude about 30" (vice the 75-80" for
40 meter operation) for an overall length of about 35 feet, 6". I'd start
with longer tubes and check first. They can always be shortened later!
This should be a snap to convert to a 30 Meter dipole if you have one of
the new hand held antenna anlyzers. If not, it's till easy with a
transceiver. Just move the minimum VSWR point to your favorite 30 Meter
freqeuncy.
Let me know how it works.
73, Joe, W1JR
>While we are looking at "new" products. Has anybody tried retuning the
>Cushcraft D40 rotary dipole to 30M? I understand the unit contains a
>coil and not a trap and perhaps removing the capacity hats and minor
>retuning of element lenghts may be all that is required.
>
>de Brian/K3KO
>
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