[Boatanchors] Coax Switches and Wire Antennas

[mac]

Bill,

OK.  Been a while since I've run across anyone using the old single  
wire fed Windom.  Used one myself back in the 50's with good results  
as I recall.  Same configuration called out in the SCR-284 manual.   
Back in the 1930's the U.S. Forrest Service used them too.

On the half wave end fed yes, feeding right at the high impedance/high  
voltage point.  Essentially the same situation if you stretch the wire  
out to a full wave.   On a quick calculation you could seeing  
something like 500 volts peak  with 75 watts into the end of the wire  
(est. 2500 ohms input Z).  Probably get away OK with the coax switch  
at that power level unless one of the small, cheap CB models.  Gary's  
idea of a sheet of plexi with banana jacks a better way to go, though.

I've been using "voltage fed" wires for years, BTW. with power levels  
up to legal max (something like 2500 volts peak at the feed point).   
Use an "L" matching network at the base of the antenna and coax from  
there into the shack.

Good luck.

Dennis D. W7QHO
Glendale, CA

*************

On Mar 30, 2011, at 4:19 PM, Bill Stewart wrote:

> Tnx Dennis for the response.
> I use the classic windom for some of the homebrew rigs and it works  
> quite well. In the coax switch situation, I will probably be using a  
> simple 80 mtr half wave wire, which has the max voltage at the feed  
> line end..so, maximum arcing possibilities. I may expand it to a  
> full wave just to see how it works..more length dependent on tree  
> density. I'm using low power xmtrs such as the AT-1, Lysco, Globe  
> Chief 90A, etc, so no big power. I will be using it on harmonically  
> related bands. I do use some knife switches, but it takes several  
> with the number of xmtrs I will be using.
>
> 73, Bill K4JYS
> ----- Original Message -----
> From: "mac" <w7qho at aol.com>
> To: "Bill Stewart" <cwopr at embarqmail.com>
> Cc: "boatanchors" <boatanchors at mailman.qth.net>
> Sent: Wednesday, March 30, 2011 4:40:24 PM
> Subject: Re: [Boatanchors] Coax Switches and Wire Antennas
>
> Bill,
>
>  If you plan to use the classic Windom (half wave top section, single
> wire feeder) the impedance looking into the feedwire "should" be
> something around 600 ohms. Cut and try required to find the correct
> tap point on the flat-top and the length of the feed wire and the
> ground system used also have an effect.  Probably OK through your coax
> switch at the 75 watt level but only for the frequency/band for which
> the flat top was cut.  On harmonic related frequencies (ex. 40M
> operation on a flat top cut for 75M) the impedance looking into the
> feedline could be just about anything.
>
> For the end-fed case, how long is the wire and what frequency/
> frequencies are you using?  OK for your switch if the feed point is
> anywhere near a current loop.
>
> Dennis D. W7QHO
> Glendale, CA