Peter, You are right about the 22 kHz image in transmission. That is why I am reluctant to transmit without checking (and adjusting) the attenuation on the used frequency.
With the preamplifier board the leakage of the sampling signal still can be detected by my other receivers. In practice it is no problem on the usual noisy bands. That is true also with the 1/f-noise, if you are running with the gains now used in the SDR-1000. In my earlier experiments with zero-IF I tried to maximize the dynamic range without any preamplifier. Then the 1/f-noise determines your weak signal performance. The maximum signal will be about 4 Vpp at the 200 ohm level that the QSD sees and can handle. This makes about 0 dBm at the antenna connector. Just for an explanation, this experiment was made for a commercial instrumentation project handling about 20 kHz bandwidth. If you have a SoftRock receiver available, you may tune across the 0 Hz IF. With the present high gain opamp you hardly can see anything special. Try to set the gain to 0 dB, then you possibly will find a difference. Measure the signals before the sound card. 73, Ahti OH2RZ On 21/05/06, Peter Martinez <[EMAIL PROTECTED]> wrote: > >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 > _______________________________________________ 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
