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[Amps] swr

To: amps@contesting.com
Subject: [Amps] swr
From: "c." <carlseye@tampabay.rr.com>
Date: Thu, 04 Jan 2007 15:00:01 -0500
List-post: <mailto:amps@contesting.com>
      I've been following this thread on input swr VS. cable length. 
I've seen this many times but what has apparently not been considered is 
the capacitance per foot of the cable, which is in the range of 25-30 pf 
with the RG8 series of cables. That means 20 ft. of cable has around 600 
pfs.All that is being added to the input side of the pi-net inputs used 
in most amps.. When I see that problem My approach is to go into the amp 
and change the capacitance values as needed , especially on the exciter 
side of the pi-net.!!! I know that in the past some mfrs. have specified 
a certain length of coax for their amps, which of course could have been 
due to a couple other reasons, but I don't like having 20 ft. of coax 
running loose in my setup. Six ft. of cable is plenty for me. Of course 
, if you sell your amp after modifying it then the next owner will be 
asking the same questions as have been asked here already.!!!
       I also have noted that some folks have changed to a parallel 
tuned input ckt and have wondered what the swr must be like.!!!!If the 
ckt is resonant in band will the swr be low ??
        just another thought.!!!
           any comments??
      carl / kz5ca

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