Re: K3 Autotuner malfunction

Posted by Rob KK4R on Jul 05, 2015; 4:18am
URL: http://elecraft.85.s1.nabble.com/K3-Autotuner-malfunction-tp7604565p7604624.html

Don,

At first (months ago), I looked at the antenna impedance at the rig and thought that it was a problem.  It was an 80m horizontal loop fed with 450 Ohm line.  It would be problematic to change the feed line length, so I did some calculations and found that 300 Ohm line would provide a better match on most bands.  The line was changed and the loop length trimmed a bit (not enough).  The VSWR was measured across the HF spectrum with a good network analyzer.  The result looked good.  On 80m, SWR ranged between about 7:1 to 3.5:1.  On forty, it was between about 4:1 and less than 2:1.

After reading your message, I checked the impedance and SWR again a couple of ways, and although it isn't as good as from the network analyzer, the data agrees pretty well.  If anything, the SWR looks better now.  The bottom line is that the impedance isn't bad, and I barely need the tuner on 40m at all.  In fact, the tuner might be confused by the low SWR, I suppose.  Using a tuner with a good load breaks the rule, "If it ain't broke, don't fix it!"

The antenna impedance magnitude is between 25 and 80 Ohms in both bands.  I could email you the SWR plot I made when the new feed line was put up, if you are curious.  Too bad I didn't measure S-parameters.

73,
Rob