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[Towertalk] Re: [Towertalk] Pattern

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Subject: [Towertalk] Re: [Towertalk] Pattern
From: (
Date: Tue, 10 Sep 2002 17:19:35 +0200
Hi Dan,

I've no experience with boom loaded dipoles, but with self supporting 
loaded dipoles on low bands yes.
I think a 140 ft high dipole on 80m will be an efficient transmitting 
antenna meanwhile I doubt it will be the same good "tool" as a 
receiving antenna.
Actually, the theoretical dipole figure 8 pattern with deep nulls in 
free space at zero angle doesn't match with real dipoles over ground 
although half wave from ground is probably the best among the real 
Also a pair of end fire verticals aren't comparable in directivity with 
3 or 4 ones since the -3dB aperture is quite wide.
In my experience what counts to receive is overall directivity, nulls 
are good to notch some local noise rather than to decrease fields from 
sky waves and gain is quite a relative issue.
Of course anything is better than nothing and a dipole at 140ft is more 
than anything.
Anyway, if you have the room try a short simple terminated beverage, 
some 300 to 500 ft of copper wire 6ft over ground will give you a 
totally different reception, just another world compared to the high 
dipole or to a couple of verticals.

Mauri I4JMY

> I have recently acquired a good used KLM 20M6 (57 ft boom). I plan to
> put it at 140 ft and load the boom for 80m as a rotary dipole, after
> connecting the end elements to the boom. I have a 4 el 20 at 60ft on
> another tower. In your experience, have  boom loaded yagi/dipoles show
> sharp end nulls as you would expect from a linear dipole? Have you eve
> measured or estimated the end nulls. Obviously I am interested in
> whether these T dipoles have the gain of a dipole over an
> omnidirectional vertical. I have a full size 2 el vertical array for 8
> which works fairly well but think the high dipole might be better,
> particularly for receiving. 
> 73, Dan, N5AR
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