Roughly speaking, if one is talking about the impedance looking into a typical grounded grid linear amp, the driving impedance begins to vary considerably as the driving signal negative peak voltage lessens approaching the tube's grid cutoff voltage plus cathode bias, and a larger and larger percentage of the drive cycle is in the tube conduction range. This is more obvious on SSB if the amp has a higher cathode bias value for CW.
The input network for the amp is generally tuned to match power and conduction cycles when driving the amp to full output. 73, Guy 2009/7/18 K2QI <k2qi....@gmail.com> > Björn's description of the KPA3 behavior sounds incredibly similar to > issues > I've been experiencing when only operating in sideband. My problem however > isn't so much of an initial low power transmit, but what appears to be the > complete opposite. Some of you may recall the post I submitted to the > reflector several days ago about strange RF activity and my K3. In a > nutshell, my SWR alarm on my wattmeter will trip upon initial keydown when > operating in sideband and the linear is on. It functions fine on the other > hand if I key down with a continuous carrier.. even up to 1200W. The > exciter drive level doesn't seem to make too much of a difference UNLESS I > turn the power output to 12W or less. The moment I switch back to 13W or > higher and the KPA3 is in line, the problems begin. Looking at my > wattmeter > in peak mode shows an initial burst of power when keying down. After a few > seconds, the power drops back to a normal level. I have a theory that > there's some sort of RF burst in sideband mode upon initial keydown; > perhaps > the KPA3 oscillates for just a few seconds and transmits off-frequency > until > it stabilizes. This is just a theory though. > > I'm still playing with my RF grounding and isolation to fully hope in > eliminating all other possibilities before pointing the finger at the K3. > > 73 de James K2QI > > ______________________________________________________________ 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
