[Boatanchors] Coax Switches and Wire Antennas

[Bill Stewart]

Dennis, 

I have been using the classic windom or Off Center fed Hertz, for about ten years. It was the antenna suggested for the 1929 TNT osc I built. It works very well and is only about 30 feet up in amongst a bunch of pines. It's a simple antenna and easy to hook up to the '29 rigs and other homebrew one tubers I have built. 



Tnx for the voltage est. I have several good ideas to try. May even try a good quality coax switch if I can find one at a good price. Tnx to all for your input. 

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 8:03:03 PM 
Subject: Re: [Boatanchors] Coax Switches and Wire Antennas 

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