Re: [TowerTalk] SWR variations with power

[Grant Saviers <grants2@pacbell.net>]

Any ferrite baluns, ununs, chokes on the feedline or at the antenna?  At 
2K power levels you could be heating them up (or saturating something) 
and changing the Z.  Different frequencies will behave differently, 
also.  The time constant of the change may yield some clues and you can 
scan suspects with an IR thermometer. (about $40 at Harbor Freight).
How do you like the 2K-FA?  reply off list.

Grant KZ1W

On 11/4/2013 1:03 PM, Rick Kiessig wrote:
> I have a power/SWR meter in my amplifier (an Expert 2K-FA), as well as an
> off-board Power Master.
>
>   
>
> Both meters show that the SWR level fluctuates somewhat as the power level
> changes - getting higher with more power. for example, the range might
> bounce around between 1.2 and 1.4 as I talk on sideband at 1 kW, vs. close
> to 1.0 after the auto-tuner in the amp runs (generally with 20 to 50W
> input). It seems to behave a little differently on different bands.
>
>   
>
> Changes at the Power Master appear to be dampened somewhat compared to the
> amp's meter, but they are there.
>
>   
>
> Is this normal? If not, what could cause that kind of thing? A poor
> connector or a weak coax segment? My station is fairly close to the tower
> and antenna. Could it be related to RFI intrusion?
>
>   
>
> A TDR sweep using an AIM 4170 shows an impedance bump on the near end of the
> coax, perhaps from the Power Master coupler - but nothing else that looked
> unusual. A "regular" AIM impedance sweep also looks OK.
>
>   
>
> If the SWR fluctuations aren't normal, suggestions for chasing them down
> would be appreciated. I've thought about putting a dummy load at various
> points in the coax run, but it would be a fair bit of work, so I'm hoping
> there's a better way.
>
>   
>
> Regards,
>
> Rick
>
>   
>
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>
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