R: [TowerTalk] Beverage Questions (Revisited)

[Maurizio Panicara]

-----Messaggio Originale-----
Da: Chuck <dietz@texas.net>
A: Maurizio Panicara <i4jmy@iol.it>; Tower Talk (mail list)
<towertalk@contesting.com>
Data invio: marted́ 4 gennaio 2000 14.48
Oggetto: [TowerTalk] Beverage Questions (Revisited)



> How do you short the end of a single wire?  If I short it to ground,
> there will still be thousands of ohms of resistance through the ground.


To find out line lenght using line properties, what you look for is the
frequencies in which the transformed impedance, at load side, is minimal or
maximal. The measured impedance at peaks is not relevant.
Naturally if your beverage were a two wire you might overcome the "lossy
ground problem" shorting the two ends of the wires together and measuring at
the other edge so neglecting the ground. In such case the real short will
produce more defined low/high impedance peaks in your instrument.
Although in a single wire beverage one of the "line" wires is a lossy
conductor, a short to the ground better fixes the load position along it
than an open circuit does and takes away the uncertaintinity about the
lenght. Even if smoothed, infact, the impedance peaks (frequency dependent
only) have to exist and are related to line lenght, not to conductor/s
resistivity.

>
> So, I should put the analyzer at the antenna and adjust the transformer
> ratio first?  Or try to flatten response by varying the resistance?  The
> SWR seems to be lower above and below the 160 meter band.
>

"The load resistor in a terminated beverage affects the F/B. Varying the
resistor for matching purposes could negatively influence F/B".

First step is to roughly calculate what the antenna impedance should be with
a certain wire diameter placed at a certain height over ground, providing
the proper termination load and the proper matching transformer.
Second step is to verify if the antenna works checking if the SWR response
doesn't vary abruptly changing the frequency and if a reasonable F/B is
present.
If the second point has been achieved, the final step can take place.
In the case SWR has an high value (or better to say the energy transfer
between antenna and receiver is not optimized), the transformer can be
rewound or tapped to better match the beverage characteristic impedance to
50 Ohm.

73,
Mauri

>
> Thanks again,
>
> Chuck, KZ5MM




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