[TowerTalk] SWR jumps on a 6m beam

[Mark Robinson]

I have seen something like this when I had a bad coax cable. I think it was 
the braid connection in the PL-259. I now use silver plated Teflon PL-259's 
and a higher wattage soldering iron to make the shield solder connections.


Mark N1UK


----- Original Message ----- 
From: <john at kk9a.com>
To: <TOWERTALK at contesting.com>
Cc: "Rick Kiessig" <kiessig at gmail.com>
Sent: Saturday, 29 December, 2012 10:46 AM
Subject: [TowerTalk] SWR jumps on a 6m beam


> Try it without the lightning protector.  Is this Hofi rated for that power
> level on 50 MHz?
>
> John KK9A
>
>
> To:<towertalk at contesting.com>
> Subject:[TowerTalk] SWR jumps on a 6m beam
> From:"Rick Kiessig" <kiessig at gmail.com>
> Date:Sat, 29 Dec 2012 19:52:14 +1300
>
> I have an UltraBeam UB-50 (SteppIR-like dynamic elements covering 6 to 40)
> on my tower. When set for 6m, the antenna analyzer shows an SWR of less 
> than
> 2:1 across the band. I set my TX for 50W output, and my Expert 2K-FA
> auto-tunes fine, reporting a tuned SWR of around 1.05:1.
>
>
>
> When I TX with less than about 250W output, the reported SWR stays in the
> original range, maybe bouncing up to 1.5:1 at times. However, if I 
> increase
> power to 500W or so, the amp complains about high SWR and kicks out of
> operate mode. This happens reliably, every time.
>
>
>
> Everything works fine on all other bands with a full 1000W. It's only 6m
> that's causing me grief.
>
>
>
> I'm also using the 4-element add-on kit for 6m on the UB-50, and I've
> adjusted the now-unused dynamic reflector to a non-resonant length of 
> 1.5m.
>
>
>
> The feedline is about 50m of LMR-600, with a segment of BuryFlex running 
> up
> the tower. I have a Power Master meter at the output of the amp, with a
> section of LMR-400 running from the amp to the meter that passes through a
> common mode choke (three loops through eight #31 toroids). I'm using a 
> Hofi
> lightning protector tied to a ground rod at the shack entrance. The coax
> shield is also tied to ground at the base of the tower.
>
>
>
> Any suggestions on what might be causing the problem or how to chase it 
> down
> would be appreciated. Could it be RFI getting into the amp? Maybe I need a
> larger choke (or a second one)?
>
>
>
> 73, Rick ZL2HAM
>
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