[TowerTalk] VSWR Changes with Power

[John Simmons]

Intermittent connection somewhere?

-de John NI0K

ed_richardson at shaw.ca wrote on 10/20/2019 11:06 AM:
> Finally got around to making the long awaited antenna repairs. However I now
> find myself with a strange problem.
>
>   
>
> On 15m, I have swept the antennas using 2 different handheld devices and
> measured the VSWR in the shack using both the VSWR meter in the amp and the
> standalone power master meter on the amp output.  All measurements are the
> same when using any power less than 200 watts drive from the rig and with
> the solid state amp in standby. The VSWR from 1:1 to 1.5:1 across the band
> in a normal curve.
>
>   
>
> When I place the amp on and adjust the drive, the vswr measured on the amp
> and the power master jump  to 2.3:1until I get to more than 600 watts output
> when it suddenly drops back to the expected reading.  The abnormal high
> reading is present even at power levels previously shown as normal when the
> amp is offline and the rive is direct from the rig.  Ihe VSWR = 2.3:1  amp
> on 200 watts forward. VSWR = 1.1:1 forward power  200 w direct from radio.
>
>   
>
> Increasing the power to >500 watts = 1.1:1 VSWR as expected.
>
>   
>
> Replacing inserting a 50 ohm load at the shack end of the antenna system
> feedline results in normal performance regardless of the power output.
>
>   
>
> I thought I might have been seeing a balun saturation problem which is why I
> am posting on this group. However getting different results with the same
> power originating from the amp or the rig perplexes me.
>
>   
>
> Suggestions on where to look?
>
>   
>
> Ed VE4EAR
>
>   
>
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