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Re: [Amps] *** SPAM *** Re: Alpha 87a

To: <amps@contesting.com>
Subject: Re: [Amps] *** SPAM *** Re: Alpha 87a
From: "Tom W8JI" <w8ji@w8ji.com>
Date: Tue, 2 Jan 2007 20:17:34 -0500
List-post: <mailto:amps@contesting.com>
> Tom said:
>>Currents on the
> shield can't change SWR inside the cable <
>
> This is very true: however, what they can do is to change 
> the indicated SWR, depending on the SWR meter. So you can 
> have a cable that in reality has a 1:1 SWR, but has an 
> indicated 1.5:1. This fact is not always appreciated..

CM currents can only affect the meter if it is really messed 
up and totally unreliable. I've never seen one like that 
yet, although I can imagine how one could be made to work 
that way. One way that *could* happen is a meter with a 
remote indicator and no bypassing on the interface line, so 
the shield voltage is rectified and detected by the poorly 
bypassed external leads....but that wouldn't be a good meter 
to use around any antenna.

Common mode currents cannot affect the SWR reading unless 
they are involve a radiating load and they are actually 
changing that load's characteristics....but in this case the 
SWR is really changing.


73 Tom


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