[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE:I-Q and HF SSB/AM/FM questions, bulk buy for 200Mhz SAW oscs
- Subject: RE:I-Q and HF SSB/AM/FM questions, bulk buy for 200Mhz SAW oscs
- From: Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx
- Date: Fri, 4 Jul 2003 21:27:27 +0200
> > For AM you can use coherent processing but FM does not work right now.
> Could I not just use it in SSB/CW mode and use AFC to match the carrier
Yes. This is what I mean. You only have "weak signal cw" but by
enabling AFC and coherent processing you will have coherent AM detection.
It will be possible to do FM also but only if the modulation
index is very low and the carrier stable.
> The beat frequency of a carrier-LO (ie zero frequency in my case)
> doesn't bother me too much, but it would be nice to be able to
> lock it in for listening to AM Broadcast
Should be no problem:) That is what coherent processing does.
> > There is no AGC in weak cw mode so you will not have the AGC that should
> > be in place in "normal" modes. There is an RF clipper at the output
> > however so SSB works pretty well without AGC.
> Is there a problem with using normal mode for SSB? I presume I
> just have to
> increase the bandwidth of the first FFT... unless that is just
> the frequency bucket size?
No. The size of fft1 and fft2 does not matter - as long as your computer
is fast enough. You just have to make the baseband bandwidth big enough.
> > You just click on the SSB signal to get it in the loudspeaker.
> > I have planned for an automatic BFO setting in SSB mode and some
> > other fancy stuff but everything takes time....
> Ah, I see. So the AFC will only help control the output frequency
> of a single tone I assume...
Yes. Such as the carrier of an AM station.
> No matter for SSB,
Sure. The carrier is absent. One will have to "guess" where it is.
> and I could probably cook something up
> soldered to my soundcard for AM that would sample the low beat from a
> mismatched carrier in AM and tweak my reference oscillator a
> little to tune it back.
No no. When you set your LO to a frequency close to an AM station you
will feed a 40kHz wide chunk of the RF spectrum into Linrad.
You are free to click on any of the AM stations that are present
within the passband:)
> > What does 5ps mean in terms of phase noise? How many dBc/Hz at 20kHz?
> > Just curious.
> I really have no idea how this would be calculated - I'm really just an
> experimenter looking to build an effective but low-cost
> computer-controlled GCR. All I know is that in the SDR-1000 design that
> pretty good phase noise
> can be achieved due to the AD9854's 12 bit DAC and other improvements,
> improved over the AD9850/1's 10 bits. The author implies that a
> really low
> jitter reference will be required to take full advantage of this.
> The datasheets are at:
I do not know either. I find it very hard to believe such a small
thing can be particularly good. As them what the phase noise is...
> The jitter, by comparison, is extremely low at these kind of
> frequencies, from all the alternatives I looked at. The only
> better alternative was Valpey-Fisher (1ps RMS jitter), and
> they quoted me UKP 48.00 each, min.order 10. Way beyond my means.
Did not someone else specify both time jitter and phase noise?
Leif / SM5BSZ