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

[Tom W8JI]

> 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