[TowerTalk] Reflector element question...

[Stan Stockton]

Geoff,

The length and the diameter and length of each diameter (taper schedule) 
will affect the performance.  You would not want to look at the overall 
length dimensions for elements of a 6m design in the handbook and then 
use tubing of the same length that is twice the diameter.  With the 
right dimensions, however, you can make what you have work well - 
perhaps even better than what you would have had using the smaller 
diameter tubing the article calls for.  I have no idea where that 
particular antenna has its best gain or F/B but you can certainly 
adversely affect both by making the reflector a different electrical 
length than what the design calls for.

I just looked at a design of a 5 element 6M Yagi that had 31+ dB of F/B 
at 50.1.  Increasing the length of the reflector by 2 inches overall 
dropped the F/B by about 6 dB.  Generally speaking increasing the length 
will help the F/B at a lower frequency than where it was previously 
best.  For example, while it dropped 6 dB at 50.1 it got better at 49.9 
by about 4 dB.

Stan, K5GO


----- Original Message ----- 
From: "Geoffrey Way" <wayg at cape-vision.com>
To: <towertalk at contesting.com>
Sent: Friday, September 10, 2010 3:14 PM
Subject: [TowerTalk] Reflector element question...


> I'm converting an old Moseley CL-33 tribander into a 6m beam.
> It has a 12 foot boom, so I'm following the suggested layout in the
> ARRL antenna book for a 5-element design shown on p. 18-27 of
> the 2007 (21st) edition.
>
> My question is, if I have some extra length on the reflector element,
> would I get any additional front to back ratio if it were longer? And,
> is there a length that becomes too long, having some adverse effect?
> Or is it just a case of no further benefit? Perhaps some other effect
> that I am unaware of?
> -- 
>
>             Geoff Way, KA1IOR
>
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