Mark, I have had some problems with PA oscillation around 5.6 Mhz if the power supply voltage fell below 13 volts. The frequency of oscillation was dependent on PA voltage and NOT drive frequency. I solved it with a little extra bypassing on the B+ lead at the PA.
73's Mark NU6X -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mark Amos Sent: Wednesday, August 01, 2007 3:52 PM To: FlexRadio@flex-radio.biz Subject: [Flexradio] Transmit problem Flexers, I'm having a transmit problem with my SDR1000. Here's the lineup: SDR1000 with all the options (ATU, PA, RFE, transverter) Edirol FA66 USB cable All audio lines isolated between computer, Edirol and the radio. Ferrite clamps on all of the audio and control cables. Radio gear, computer, tuner, etc. all connected to common shack ground. Palstar tuner Butternut vertical The problem is that on 40 Meters, when I key the transmitter, the forward power goes up over 200 watts with any setting over 10W "drive" setting. At that point the SWR (as shown on the Palstar and on PowerSDR) goes through the roof, and the power output from the Flex does as well. It ONLY happens on 40 meters and ONLY when connected to the antenna (i.e. there is no problem transmitting into a dummy load.) I substituted a dummy load at each location between the transmitter and the antenna and thus ruled out issues with the coax, bulkhead feedthroughs, tuner, etc. So, it appears to be an antenna problem (perhaps a short or open that only shows up at power above 10 watts...) What puzzles me is the SDR1000 cranking out such high power (as reported by PowerSDR, the tuner and an in-line wattmeter) under a high SWR condition. PowerSDR shows "High SWR" on the panadapter display, but doesn't cut back the power. So, here's my question: would an RF feedback / antenna problem account for this behavior? Mark _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
