[Elecraft] TUNE power, low vs high

[Jack Brindle]

The answer is pretty simple. The higher the output power, the more resolution for both forward and reflected power measurement. 
When calculating SWR we can get some pretty small reflected power values that may still produce a pretty high SWR. In order
to get something that provides reasonable results, you need a bit more power. If you tried doing the measurement with 0.8W of forward
power there wouldn’t be enough reflected power to measure.

One way to really see this is to try to tune at very low power, then increase the power. You might be surprised to see a pretty high
SWR that looked pretty good before. So, the more forward power you have, the better the tune will come out. Of course there is a limit.
You don’t want to put too much power through the tuning relays.

73!

Jack Brindle, W6FB




On Dec 12, 2013, at 4:34 PM, Arno Dienhart <adienhart at gmail.com> wrote:

> What could be the difference for the tuning result between tuning at, say,
> 0.8W vs at 3W?
> 
> If there is no difference, why is the ATU tuning set to 2 or 3W, and not
> lower?
> 
> 
> 
> I am thinking that a random length antenna with a potentially high SWR will
> tax the PA more at higher outputs. So why shouldn't I use a low output,
> always (besides causing less QRM then)?
> 
> 
> 
> 73 de Arno K7RNO
> 
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