Dave Tweed dtweed.com> writes: > Your enthusiasm is causing you to extrapolate way beyond the concept > of the original project, which was to evaluate the details of a crystal > filter's amplitude response, which was already known to be less than > the bandwidth of the sound card. This isn't a "spectrum analyzer" so > much as a magnitude-only "network analyzer" (no phase information). > > In order to turn this into a direct-conversion spectrum analyzer, > you'd need to build a filter with a fixed 20 kHz bandwidth whose > center frequency could be varied from "DC to 1 GHz". Good luck! > > If you want a rather good design for a low-cost spectrum analyzer, > as well as a discussion of some of the design issues, look for the > article by Neal Martini in the next issue (#192) of Circuit Cellar. > It's based on a MAX3550 and a PIC18F4520. Thanks for answering. My enthusiasm is that of an optimist with experience. I have specan experience with homebrew, HP, and Elbonian devices. I think that I know what can be built, bought and rented, and what it's worth. My question was, assuming this is a $20 project including 1 hour of soldering, and that it will be used for low signal work, in closed circuit (not exposed to QRM for example), and that the user can always turn off the power to the DUT and to the signal source if suspecting something is not right about the output, are there any serious flaws in this scheme, which would prevent it from being used to tune VHF, UHF and microwave circuits using the noise input method (noise which is inherently incoherent and thus makes an IQ demodulator unnecessary) ? As to the CC article, thanks for posting that. Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist