Hi Martin, This topic passed through the group a couple of weeks ago. Don has some very good comments on it.
I can make a few *un-official** comments based on my own limited experience. I am a K2 owner rather than a K3 owner, however, I have a hunch the SWR circuits are close approximations. The K2's SWR circuit has the typical line passing through the center of a toroid with a couple of trim-caps and diode FWD/REF rectification. What is tapped off this are FWD & REF voltages. The typical SWR circuit in an external tuner is almost identical, except that the FWD & REF energy is tapped off as a current which is then series_R limited (trim-pot) for driving an analog meter. The (trim-pot), in all probability was tweaked to adjust the analog meter reading with 100 watts applied. Long story short... I use an outdoors mounted auto-tuner, and I wanted to watch it adjust SWR when I switch frequencies. So I built myself a tiny analog SWR meter using one of the MFJ meters and a modified rectifier circuit. I wanted to test its readings up the scale to 100 watts. Don reminded me of the voltage reading that can be taken on a dummy load (non-reactive resistance) with an HF probe and a scope. IF you have a scope, give it a try. Just tap across the dummy. Set the probe to 10X so there is no circuit loading. wattage = (mV reading * mV reading)/400 This assumes an R of 50 ohms. HAVE FUN!! :) Duane N1BBR -- bw...@fastmail.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
