[Antennas] questions on Windom

Tue Jan 4 00:34:21 EST 2005

The 22ft length of coax is evidently used by the antenna as a radiator or
xmfr in those bands where the Z is not 50ohms..
A common mode coaxial choke will kill any radiation on the SHIELD of the
coax....thus the 22ft above it can radiate...where as the coax below the
choke, will not.
Yes the off center feed does move the feedpoint away from a current null or
peak...thus moving the feed point to a spot that will not be too high a Z at
most freqs..and low at others...No the current peak is not centered on the
bands..the move off the center of the dipole at the lowest freq makes the
feedpoint OFF the max current and thus shifts the feedpoint imepdance on
those bands harmonically related....(even harmonics of a normal dipole are
HIGH Z; odd harmonics are low Z...shifting off center makes the Z somewhat
more avergaed over the various bands...at least that's the theory! :)
As for 160, I would call it a top loaded 22ft vertical myself...but the top
loading is not symetrical....Not really sure what the current distribution
would be on that..It's a shortie no matter which way you look at it :)
Chris
WB5ITT
> -----Original Message-----
> From: antennas-bounces at mailman.qth.net 
> [mailto:antennas-bounces at mailman.qth.net] On Behalf Of RB
> Sent: Monday, January 03, 2005 11:25 PM
> To: antennas at mailman.qth.net
> Subject: [Antennas] questions on Windom
>>> I have a 136' (1/2 wave on 80m) Carolina Windom from Radio 
> Works. It's a good antenna, and works well for me. 
>> There is a transformer or balun at the feedpoint (14% off 
> center). Then, a 22' coax downdrop to a choke balun. Coax 
> on to the shack. 
>> What function does the choke balun play? There's coax on 
> both sides of it. I thought unbalanced signal goes in one 
> end of a choke balun, and balanced signal comes out. Having 
> coax on the balanced output side of the balun would seem to 
> be counterproductive. But, it works, and works well. How/why? 
>> Does the off-center feed shift the current peak over by the 
> amount of offset on some bands? Is the current peak 
> symmetrically centered on some bands? What is the effect of 
> off center feed? 
>> The antenna is rated for 160m use, too. What do I have when 
> on 160? Is it sort of a 22' top loaded vertical? It's a 
> shortie, physically, for 160, if you consider only the 
> horizontal part. Likely very reactive---which is why power 
> input rating on 160 is only 500 watts.