On Sat, 16 Oct 2010 15:43:01 -0400, Garey Barrell wrote: > >Is that a possibility? If the antenna is tuned to 20M by the tuner, and >the transmitter is putting out 40M RF, then the transmitter is seeing a >mismatch and 'shuts down'. Does it 'really' go to ZERO power or is it >just rolled back to 20 or so Watts?
Actually, the oscillation seems to be inherent in the bandswitch segment that covers 40 Meters. I was able to see it in any 500 KHz segment of that range, and the actual frequency of the oscillation was in the area of 9 MHz, regardless of which 500 KHz segment of that range that I was in. So, any antenna resonant in a ham band would have high VSWR at the freqency of oscillation. In power testing on a dummy load, I did seem to see a shallow peak in output around 9 MHz, and for some reason this is what suggested to me that the gain somewhere in the predriver might be too high in that area. I ceased further investigation once I found a fix that worked. Maybe somone who has the proper software could model the REV. 2 predriver and see what crawls out. >BUT, if you put 40M RF into a tuner set for 20M why would the external >power meter show high reflected power? Unless enough 40M RF is getting >through the tuner to see the mismatched antenna.... > >My head hurts.... Worth looking into. What puzzles me is the behaviour of the forward power meter. IIRC, in the units that I had here, the forward power was quite high when it was oscillating. Almost like full power CW. Maybe it's some difference in the way the rigs were adjusted. WTF? Interesting problem. 73 -Jim -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime." HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://radiojim.exofire.net http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
