>From G3PLX: I just checked my two soundcards for the low-frequency roll-off. My new Firebox is 2.4dB down at 1.8Hz and the MP3+ is 1.5dB down at 1.2Hz. And that was done quickly by linking line-out to line-in, so it includes the LF roll-off of the transmit side too. I am quite certain the music business wouldn't touch a soundcard that rolled-off at 200Hz.
The LF roll-off is really not a problem for zero-IF anyway. Even if you put the oscillator right in the centre, which theoretically puts a deep narrow null in the passband, I defy anyone to notice it's there on an SSB signal. There are ways to eliminate this null completely, but I really don't think we need to do it. To Ahti: I have never seen 1/f noise in my zero-IF work (I designed such a receiver before I retired, for HF GMDSS working). The local oscillator radiation problem looks just like 1/f noise, but that can be fixed once it is recognised. It's also possible that poor post-mixer design could result in supply-line noise being a problem (this has a 1/f spectrum), but the post-mixer amplifier design of the SDR1000 kit is excellent in this respect. If 1/f noise was present, it would show as a noise peak at the centre of the output spectrum. There is no such peak. If, as Frank says, the SDR1000 software can do zero-IF already, has anyone done any tests with it? What were the results? Were there any problems? Has the local oscillator radiation problem gone now that the RF amplifier is in place? I think it's worth looking at this area again. The 22kHz image problem will be tolerated by SDR1000 fans but this is surely not a proper solution. My GMDSS receiver would not have gained it's approval certificate if the operator had to balance the image rejection each time he changed bands! 73 Peter _______________________________________________ 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
