[Antennas] Change in coaz = change in SWR.

Sat, 26 Oct 2002 20:39:43 -0500

If changing the feed line causes the SWR to change,
1) the antenna is NOT resonant at the desired freq and the coax is
tuning it OR
2) the coax is radiating..

either way, double check SWR AT THE ANTENNA if you can....also double
check the antenna length....it should be close to what the actual
figure is of 468/freq = length in feet overall....of course this varies 
due to height above ground and surroundings near the antenna field.

A good choke balun at the antenna may also help (wind the coax about
9 times or so around a oatmeal container...round of course :) and tape
it so it stays in that shape...that will act like a choke to the RF
and hopefully kill any radiation along the feedline (some snap on
iron core chokes will also work..)

Chris
WB5ITT

Thomas Beltran 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
> 
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