Da: Chuck <firstname.lastname@example.org>
A: towertalk <email@example.com>
Data invio: lunedì 27 dicembre 1999 1.29
Oggetto: [TowerTalk] Beverage Questions
> 1. I have a NE beverage which is about 14 ft high
Actually, 14 ft is too high not to lose a part of the beverage benfits due
to the antenna response to other unwanted modes. Lower the height, if
possible. Best is between 4 to 8 ft.
>I have used the AEA Analyzer on the beverage and
> observed that when it is not terminated there are "dips" to low SWR at
> 1650 khz and 2330 khz with the lower freq. being a sharper dip to a
> lower SWR. Does this mean I probably have an odd multiple of a 1/4
> wavelength at those freqs?
> 5/4 W @ 1650 = 745 ft
> 7/4 W @ 2330 = 739 ft
> Perhaps I have about 740 feet out?
To estimate lenght, best way is to take advantages from lines properties
that reproduces (or reverses)terminating impedance, independently by
characteristic line impedance, at each half wavelenght multiple (at each
quarterwave and odds multiples).
An open line leads to a certain degree of doubtful results as the infinite
impedance load is difficult to replicate.
The best is to short the far end, take away transformer, and measure where
impedance is minimal or maximal.
If the analyzer goes enough down in frequency, the first zero dip is half
wavelenght, the maximum a quarter.
If the analyzer doesn't go so down in frequency the first zero dip you
measure will be one wavelenght, or one and a half, or two etc. etc. and same
apply to maximums read impedances indicating the odd quarters.
A bit of common sense will help you to say which multiple can be.
> 2. When terminated with about 800 ohms, the SWR comes down to about 1.8
> to 1 in the 160 meter band. Can I fine tune the resistance of the
> termination and get this lower? Does it matter when it is already below
> 2 to 1?
No, at this point SWR minimum doesn't matter and the correct procedure is
not to lower SWR (your transformer could be a wrong ratio) but finding out a
terminating resistor that flattens the SWR response along the widest
Found such terminating resistor, the SWR can be minimized (reasonably)
changing the tap on the input transformer.
In your case, since the used 14 ft wire height, hardly it's a 9:1 ratio.
> I have room for a 300 ft SE beverage. Would one so short work?
Not below 80 meters.
One wavelenght long beverage somehow works and it's better than nothing.
> Chuck, KZ5MM
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