Hi Gerald, I don't think Jon's problem is one of TX Image Rejection. We nulled it down at least 70 dB using the procedure in the manual. But we're still seeing grunge on the opposite sideband. If I listen to that sideband on another receiver, it doesn't sound like a clear voice (as I would expect if, say, there was an I/Q imbalance that would produce sort of a DSB effect). Instead, it kind of sounds like SSB when you receive it in AM mode - you can tell it's a voice, sort of, but it sounds very very bad.
My current hypothesis is that it might be PA IMD. Wish I'd looked at the spectrum pre-PA (at the QRP Output connector) yesterday when we had it on the bench, rather than looking only at the output post-PA. - Jeff, K6JCA. --- Gerald Capodieci <[EMAIL PROTECTED]> wrote: > There is a procedure for Transmit Image Rejection > management on the bottom of page 90 of the manual. > It worked for me but I'm using a Delta 44. The > section was rewritten by Eric but not published yet. > Just use another trusted receiver, tune it to the > same frequency but the apposite side band and adjust > the SDR slider controls to surpress it. > > K6JEK <[EMAIL PROTECTED]> wrote: Here is an update > on the poor sideband suppression from my SDR-1000. > It is putting significant energy out on the wrong > sideband, visible in > the panadapter of a nearby fellow Flexer and audible > by not so nearby > hams listening on the opposite sideband. > > Yesterday I took the radio over to Jeff, K6JCA's, > impressive lab. > Together we used as many pieces of test equipment as > we could think of > -- HP spectrum analyzers, lab grade audio spectrum > analyzers, signal > generators, and most effectively of all Jeff's SDR > 1000 to see what was > happening with mine. We haven't completely solved > the problem. But > here are the weekend's revelations: > > 1) It not the opposite sideband. Listening on the > opposite sideband > sounds like SSB through an AM detector > 2) Wide band noise was coming out of the Firebox. > The little filter > on the line-out line knocked it way back. > 3) Audio coming out of the Firebox looked really > good on the lab grade > audio spectrum analyzer -- brick wall, no funny > business -120 dBV > noise floor (with the filter) > 4) Careful adjustment of the TX Image dropped the > opposite sideband > signal by quite a bit, 10 - 20 dB > 5) Jeff's radio has some of the funny opposite side > signal too > 6) Jeff has too much stuff > 7) Two hams can spend an afternoon pushing RF > between radios and not > blow anything up > > _______________________________________________ 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
