[CQ-Contest] Re: [TowerTalk] 80m Dipole ssb/cw switching

k8cc k8cc at mediaone.net
Wed Nov 14 23:18:22 EST 2001

At 06:59 PM 11/14/01 -0500, Tom Rauch wrote:
>I spent some time modelling that idea, and using a Smith chart it
>really doesn't work very well...at least as he described the concept.
>The SWR does not improve that much, and the voltages are
>beyond the limits of a receiving variable and it requires over 1000pF
>of capacitance. The major problem is the feedline between the
>antenna and the tuning cap is only 1/2 wl at one frequency, and so
>it is an impedance transformation problem.


I'm surprised at those results.  The 80M dipoles I've modeled seemed to 
have R values that were reasonably well behaved over a wide range, although 
admittedly not 50 ohms.  In that sense it always seemed like simply adding 
some reactance of the opposite sign would make the antenna usable.

I don't doubt that the voltages would get rather high, but I figured that 
some HD doorknobs and maybe a vacuum variable would make it work.

Also, it always bothered me that the antenna was actually resonant below 
3500.  I figured to use the 3650-centered dipole, then add L or C as 
necessary.  But your results would seem to show otherwise.

Thanks for the note back.



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