Jay, Don't tear into it too quickly. Make some methodical tests first.
TRUISM: If you successfully obtained a null while connected to a dummy load, and then left that same dummy load connected when you checked the SWR reading, the SWR will read 1.0 - if it does not, your null was not correct. End of truism. An SWR of 9.9 usually indicates either a short or an open circuit - 9.9 is the highest SWR that is indicated by the K2. Be certain the coax cable to your dummy load is good as a first step. You could not have achieved a proper null if you have either an open circuit or a short condition, so you will have to do the null again. Before doing anything else, make a couple of 'sanity' measurements. Set the ATU menu to CALP and set to ANT1, then power off and remove the input coax to the KAT2 from the RF Board. Measure the resistance from the input coax center conductor to the center conductor of the ANT1 jack - it should measure zero ohms. Also measure resistance from the center conductor of the ANT1 jack to the shell - that should be very high (even infinite). If these measurements do not check out properly, the path is not intact through the wattmeter and relays K17 and K18 and that problem must be found before proceeding. If the above checks were good, then connect the dummy load to ANT1 and measure the resistance from the center conductor to the shield on the input coax (with the input coax still unplugged) - it should measure 50 ohms. If not, stop and find the problem. If all is well down to here, then put the KAT2 input coax back in place and try the null again. If it anywhere near normal, the slot on C55 will be within 30 degrees of parallel with the long side of the KAT2 board. If it is perpendicular to the long side of the board, then the capacitor is either at its minimum or maximum capacity point and you have a problem with T1, R3, R4, C54 or C55. As usual, T1 is the most likely suspect. 73, Don W3FPR Jay Sissom wrote: > Oops, I sent this to Don by himself, but thought I should send it to > the list just in case it helps someone. > > > > Thanks Don, just an update. I re-nulled C55 and it nulled fine. When > I checked the voltage at U4 pin 1, it was 2.8V which was a little low. > Then I set R1 & R2. After doing that, the SWR into a dummy load is > 1:9.9. I'll take the antenna tuner apart and look to see what I can > find. > > Thanks & 73 > Jay > W9IUF > > > ______________________________________________________________ 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
