Vasile Surducan gmail.com> writes: > Would work yes, but will be almost unuseless. The simple mixer must > be replaced with an IQ one, else would be necessary two or three IF > stages with all the problems. The biggest one will be the frequency > fluctuation in the audio side and the limited bandwith or distortion. > Also will be necessary a real VCO and not a white noise generator. > There are many analyzers like this one on the web, the best one is > using a tuner > and claim to work ok till 2Ghz. I'm seeing every day how works a good > spectrum analyzer (for it's 30 years old age) TEK492 and if that one > can't be used for fast signal analyses, all analyzers having the same > principle (unfortunately) can't. > So depends what do you need. I wrote: > > Finally an affordable solution for > > filter and amplifier design for homebrew UHF and microwave ? > > > > http://www.qsl.net/7n3wvm/Fil_Meas.html > > > > Peter Could you elaborate on this ? Why is an IQ mixer needed ? The way I see it the most needed thing is low (very low) phase noise of the carrier so the LO does not swamp the mixer and the audio after it (although I am unsure what happens with the phase noise in a direct conversion receiver when an actual signal is not present). The scheme is the same as used in DSB/CW direct conversion receivers, whose performance is rather good usually. Also using a noise source as input makes it possible to go to very high frequencies without the usual problems. No ? Also it is a very simple and inexpensive scheme. With a $10 mixer it could cover dc to 4GHz. If a stabilised Gunnplexer is used then microwave filter (and Gunn and varactor bias, by voltage, to match an existing filter or structure) tuning becomes possible. What am I missing ? Ok, dynamic range is probably 55dB or less (sound card dynamic range). With a good sound card and a preamplifier this could be 90-100dB. Many people already have such a good sound card. If the LO is replaced with a stepwise DSS or PLL then a spectrum can be taken with say 40kHz 'windows' from DC (almost) to 1GHz. The DSS could be controlled by a USB to parallel control for example. Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist