[Antennas] Change in coaz = change in SWR.

[Dan Richardson]

At 12:07 PM 10/26/2002 -0700, you wrote:

>I exchanged 100' feet of RG-58 with 100' of Cable X-Perts 1318FX.  After
>checking the SWR with an RF-1, there is quite a difference - the resonant
>frequency of the antenna has gone up around 600 khz.  For example, I had a
>1.7:1 (checked just before changing the coax) at 14.230.  Now that freq
>shows an SWR of  4:1.  The low point, 1.3:1, is at 14.880.  Before adjusting
>the antenna, I thought I would check with the people on this list.  Any
>ideas?  Tom W6EIJ

If the antenna changed frequencies that would suggest that the transmission 
line, or a portion of it, is part of the antenna. This can happen due to 
unwanted common mode current flowing on the outer coax braid. I suggest you 
consider using a choke/balun at the antenna's feed point to reduce this 
from happening.

Danny, K6MHE