Define 275W. Is that PEP or is that average. If it is what the meter reads the SSB peaks might be much higher. I assume you actually knew this.
Another possibility is the K3 power spike on first SSB syllable, that might be higher than the one on CW. Whenever you change mode or power setting, the ALC is reset and there is a high power spike. If that initial spike causes a breakdown, the arc will persist. However, on the second key up after a little delay to let everything cool off there should not be another arc. If there is, that was not the problem. Easy to eliminate this one. Another possibility is simple RF feedback, causing the K3 PA and amp combination to oscillate at some other frequency where the VSWR is poor. Are you wearing the headset when operating CW? If so it should happen in CW so it probably is not that either. Mike G4MKP wrote: > > Problem on 80m SSB. > > However, when I modulate the radio using SSB on 80m at anything above > approx > 275W, the SWR goes from 1:1 to infinity and I can hear the ATU flashing > over. It also occurs when modulating the radio using AFSK for RTTY > operation. Opening the ATU reveals arcing between the capacitor plates. > The > problem does not occur on any other band. > > > > Terry > > G4MKP > > > > > -- View this message in context: http://n2.nabble.com/ATU-Flashover-tp1345469p1345899.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
