[TowerTalk] Impedance difference on 4080V from Cushcraft?

[Bob Alexander]

Hi Paul,
I would say your problem is on 40 not 80.  To me, covering almost the entire
40 meter band at the 2:1 points says you have considerable losses involved.
This may sound backwards but it's not.  I just checked the manual on-line
and there is no matching device/ mechanism for the feedline so the best VSWR
should be on the order of 1/4:1 like you have on 80.  I would try adding
more radials and see if the VSWR on 40 gets "worse".  You may find that the
80 meter adjustments need to be redone.
Good luck,
Bob, W5AH

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of Dinsterdog at aol.com
Sent: Thursday, May 12, 2005 1:48 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Impedance difference on 4080V from Cushcraft?


I am going to phase a pair of 4080V verticals by Cushcraft using the W9AD
multiband phase system sold by WX0B.

But before I install the phased system, I am trying to figure  something out
about the single antenna I have up.

My impedance at resonance on 40 meters is 50 ohms with an SWR of 1:1.

My impedance at resonance on 80 meters is 40 ohms with an SWR of  1.4:1.

I have 20 buried radials averaging 30 feet, some as small as 10 feet, some
as long as 90 feet crossed over, spreading out in a 40 degree pattern going
east  away from the antenna which is next to my fence.  I have a real estate
problem.......

If you visit the website at Cushcraft, you can download the  manual.

I am trying to lower the SWR on 80M without effecting 40M.

Since I can no longer lower the resonant point by adjusting the top element
length, per the manual, I began adjusting the length of the capacitance
rods
on the 80M hat.   I have spent a lot of time already working with  them.  I
had success lowering the initial resonant SWR from 2:1 to  1.4:1. But I'm
stuck
there.

Should I just be satisfied with the performance or can I do more to improve
things?  I don't really need anymore bandwidth on 80M. I have around 80KHz
at
2:1 SWR and I only work the SSB DX window.  If this was only  for 80M, I'd
use an UNUN to get flat.  But since this is a multiband
vertical...................................

My question is more about theory with the 80M issue than anything  else.
I'm
just picky-It is just interesting to see the impedance  difference between
40M and 80M.

Just for FYI, on 40M, I have 280KHz of bandwidth  at 2:1 SWR and I am  flat
at resonance.  This antenna plays well on an analyzer, hi.

In the rain, I get a 70KHz resonant point drop on both bands- You are
warned
in the manual but not the sale's brochure- So far, I have had fun with  this
thing- Can't wait to phase them-

73

Paul  N0AH
_______________________________________________

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