[TowerTalk] "NEW" ANTENNA IDEA II

[Joe Reisert]

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
>


--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm