[TowerTalk] Gain Is a Function of Boom Length - True and Not True

[Jim White, K4OJ]

My homebrew designs all center around W2PV's theorem that the boom 
should be an odd multiple of 1/4 wavelength to achieve max gain... they 
tend to be big antennas but they seem to work pretty good :-)

K4OJ



Jim Lux wrote:
> At 05:10 PM 9/10/2003 -0400, Bryan Rambo wrote:
> 
>> I believe N0AX's statement to be true.  Thanks Ward!
>>
>> A corollary:
>> No amount of clever engineering in areas of element interaction, feed
>> efficiency, tuning networks (i.e. - traps), impedance matching gadgetry,
>> etc. can make up for a short boom.
>>
>> True?
> 
> 
> Not precisely...
> There are some fundamental limits on a combination of gain and bandwidth 
> (the classic reference is "Chu and Harrington").  You can theoretically 
> make a small, high directivity, but very narrow band  and very 
> inefficient antenna.  However, you can't get around the radiation 
> resistance problem, which makes losses a problem.  Compact loops typify 
> the problem.
> 
> And, using practical materials and practical construction, losses are an 
> issue.
> 
> Also, to a certain extent, smaller means less effective aperture (think 
> capture area), until you get to around 1/2 wavelength, where the antenna 
> can be physically smaller, but still has an effective aperture of about 
> 1/2 lambda.
> 
>> 73 - Bryan W4WMT
>>
>> ----
> 
> 
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