[TowerTalk] CM current and SWR meter changes

Steve Hunt steve at karinya.net
Fri Apr 20 09:42:52 PDT 2012


I may be wrong that it is a *direct* effect of the presence of CM 
current. Another explanation would be that changing the coax length 
alters the CM path impedance, that changes the net impedance at the 
feedpoint, and that in turn alters the SWR measured back at the shack.

Steve G3TXQ

On 20/04/2012 17:07, Jim Lux wrote:
> On 4/20/12 7:46 AM, Steve Hunt wrote:
>> Tod,
>> Typical SWR meters are affected by any CM current that is present, and
>> because the CM signal is a standing wave it can cause the meter to read
>> differently for different cable lengths. In fact if someone ever reports
>> to you that their SWR changed significantly when they changed their coax
>> length, CM current is one of the likely "suspects".
>> 73,
>> Steve G3TXQ
> What is the mechanism of the change here..

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