Sami Aintila wrote: >Peter, > >I am seeing all kinds of nasty crud around DC, and so are many other >SDR-1000 users. On some systems - maybe with some sound cards - maybe >with better grounding - the problem is not very prominent. But for >optimal (receiver) performance it's always safer to operate at some >frequency offset instead of DC. (I haven't checked the source code >lately so I'm not sure, but I think the current PowerSDR software >actually uses "0 Hz IF" for TX.) > >
This corresponds to my experiences with three different sound cards and my SDR. Keep in mind that whatever the defects of my particular receiver, it has an extensive practical lineage. In addition to all my well-documented adventures with it on HF, recall that I originally purchased it from Terry, W0VB, who performed the first moonbounce QSO with it (and in circumstances that Terry considered very challenging in terms of beforehand preparation of that famous event). So, whether mine is the best receiver that came off the line or not is kind of beside the point. Even if it is a sample size of one (three if you count sound card _types_), it has certainly been well-proven in all respects. In particular, much weak signal work has been done with it under a wide variety of conditions, geographies, and bands. Yet, I see, visually, all kinds of noise "on the left" of the panadapter display under a variety of conditions. Whatever the theory may say, my practical experience suggests that an offset from DC is a good idea. I basically ignore whatever the last kilohertz or so of the panadapter says. If I understand the display at all, it is very suggestive that Zero IF wouldn't be very successful compared to the actual implementation. Larry WO0Z _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
