[EIDXA] Feed line question

[Rod Blocksome]

Hi Jason,

Yes, over a long period of time coax loss can increase - especially if 
moisture enters the line.  As the line loss increases it will lower the SWR 
as measured at the transmitter end.

For example:  If the load (antenna feed point) has a 2.0:1 SWR and your new 
coax has 1.0 dB of loss into a matched load (50 ohms), the SWR measured at 
the transmitter end will be 1.7:1.  Now let the coax deteriorate to where 
it's loss into a matched load becomes 3.0 dB.  This same antenna 2.0:1 SWR 
becomes 1.4:1 when measured at the transmitter end.

I assume you are comparing the two antennas by switching back and forth 
while listening to the same station.  If the TH7 is at a lower height than 
the triple stack, it's possible it's gain is similar for the higher arrival 
angles.  But for really long haul stations, the triple stack should be much 
better as the arrival angle of the signal would be much lower.

If this isn't the case, I would suspect something wrong in the phasing lines 
and/or switching in the triple stack.  A good test would be to get someone 
locally (within ground wave range) and have them look at your CW transmit 
signal as you switch between the two antennas.

Hope this helps.  Call if you have more questions.

73's, Rod, K0DAS

----- Original Message ----- 
From: "Jason Joens" <pixelpaint at mchsi.com>
To: "EIDXA Reflector" <eidxa at mailman.qth.net>
Sent: Tuesday, April 02, 2013 9:21 PM
Subject: [EIDXA] Feed line question


>I have a question that's been bugging me for awhile.  What happens to feed 
>line over the years?  Can a feed line go bad over time, increasing losses, 
>yet still present a good VSWR at the radio? To the point where reception is 
>noticeably weakened? Some of the feed lines on the farm have been in place 
>for 20+ years.
>
> I've been comparing a TH7 tribander with the triple stack on 20.  The 
> difference is far from impressive, and I'm starting to wonder why there 
> isn't more of a difference.  Opinions??
>
> 73
> Jason
> Kd0mnd
>
> Sent from my iPad
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