With my SDR, 0 watts in the Tune Setup equates to 0 watts out when in Tune mode. You've probably already done this, but make sure you've clicked on the "Apply" (Or "OK") button after changing the tune power to ensure that the software sees it. Otherwise, you may think that you've changed it to 0 watts, but software may think the setting is still 35 watts.
You've described two problems: 1) Tune power should be 0, but instead fluctuates up to 35 watts, and 2) SWR on an external meter should read almost 1:1, but reads almost 4:1. Regarding the 1st problem, some possibilities are: this could be a problem with the SDR amplifier self-oscillating. What's the SWR when this occurs? Or, because the "Tune" level is set by audio from the soundcard, perhaps it could be a flakey sound-card output or bad connection between the sound-card and the Line-Out jack of the SDR, or perhaps even a very bad ground-loop? The 3/8" connectors on the back of the SDR can be flakey (mine are) - try jiggling the cables back there. (You might also try installing a Radio-Shack ground-loop isolator.) Regarding the 2nd problem (which might be related to the first): if your external meter reads almost 4:1 (and it reads 1:1 with all other transmitters), then the first suspect, in my opinion, is the SDR. And the most likely cause is that it's producing a significant amount of power at a frequency that is different than the tuned frequency of your antenna. As Jim Lux mentioned, the PA might be bad and producing a very distorted waveform (which will generate harmonic energy that will surely raise your SWR), or perhaps the transmitter is transmitting at a different frequency (here's another dumb point which you've probably already verified: make sure your XIT is Off and also that you're only operating in VFO-A mode, not dual vfo modes). I'm not sure what would cause transmission at an incorrect frequency, though. Perhaps the digital signal from the PC to the SDR (which sets the frequency) is being corrupted by noise? Do you ever experience problems setting the receive frequency? If you have an oscilloscope, I'd recommend looking at the TX waveform & frequency. Lacking that, you might try listening to it with another receiver. Good luck on your hunt. I'd recommend giving Flex-Radio a call on Monday. 73, - Jeff, K6JCA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of k5nu Sent: Sunday, January 28, 2007 5:08 AM To: FlexRadio@flex-radio.biz Subject: [Flexradio] sdr swr A question for the group. On the "transmit" tab I have the Tune set to Zero. I still have 35w output as I click the Tune button. Is that normal? Also on my external wattmeter, the power out in the "Tune" position, is very unstable. It will "flutter" back and forth by as much as 25-30 watts. This makes it very difficult to tune an amp. With the power out jumping around. etc. All calibrations have been done in the method suggested by various sdr users here on the reflector. My patience is wearing very thin. 73, Mike K5NU -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20 070128/3e02a102/attachment.html _______________________________________________ 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 Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.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 Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
