[BC] Re: No Code Vs Code Vs cutting antenna

[Richard Fry]

CBoone wrote:
>I was discussing a 1.4wave vertical antenna for the best radiation
>on a single freq....this "Extra" kept arguing to trim for lowest SWR.
>..HMMM NOW if we do that, is the antenna a true 1/4 anymore??
>Now fellow broadcasters, what happens to the pattern when the
>antenna is NOT the proper length???(I would have expected
>everyone to get that one).

There isn't much difference in the radiation pattern or gain of a "true" 
1/4-wave monopole and one that is as little as 1/10 wave.  Kraus, in 
"Antennas for All Applications," 3rd edition shows very similar pattern 
shapes for both of those, with the slightly narrower elevation pattern from 
the 1/4-wave giving it a little more peak directivity (gain) in the 
horizontal plane--e.g., 3.28X vs 3.0X, which is not much of a hit (0.8dB). 
There is a big difference in their input impedance though, which favors the 
1/4-wave to minimize system losses.

>Matching the xmtr to the feedline using a tuner introduces higher
>losses in the coax feedline.

Better to optimize the antenna match to the coax directly at the antenna 
input connector.  A variable transformer there can do that, without 
introducing matching losses.  This is commonly done in FM/TV broadcast 
antenna systems, but probably rarely by hams.

RF