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 <[email protected]> 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 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
