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Re: Topband: Beverage question

To: "'Tom W8JI'" <w8ji@w8ji.com>, "'Martin'" <dm4im@t-online.de>, <topband@contesting.com>
Subject: Re: Topband: Beverage question
From: "Lennart M" <lennart.michaelsson@telia.com>
Date: Wed, 28 Nov 2012 17:01:13 +0100
List-post: <topband@contesting.com">mailto:topband@contesting.com>
...or for a single band, instead of using ground rods, use a fair ground
radial network at the far side.
Len
SM7BIC 

-----Ursprungligt meddelande-----
Från: Topband [mailto:topband-bounces@contesting.com] För Tom W8JI
Skickat: den 28 november 2012 16:58
Till: Martin; topband@contesting.com
Ämne: Re: Topband: Beverage question

> So, how to measure the bev? Is this procedure correct:
> The bev is ~8 feet above ground. The far end is open, not grounded, no 
> resistor.
> The analyzer connects directly to the bev and the ground rod at the rx 
> end through its bnc-to-banana plug adaptor . Measure and note the 
> impedances for 160, 80, (40, 30m). Calculate the mean average.
> Calculate and install a transformer to match that value to the feedline. 
> At the far end, find the value for the termination resulting in a flat 
> swr-curve over the range 1.5Mhz - 10Mhz.
> Correct?

There are two ways to do this:

1.) measure the impedance peaks and the impedance minimums and take the
geometric mean of the adjacent peaks and minimums and average them. This is
almost certainly the least accurate method.

2.) measure the SWR variation with frequency as you adjust termination
resistance. The resistance that gives the minimal variation with frequency
(using a continuous sweep, not band by band) will be the proper termination.

In all cases, be sure you have reasonably good grounds. Several spaced rods
or a few short buried radials and some rods will generally work, ground
resistance only has to be less than 50 ohms or so. 

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