Bill, On 12/09/2013 02:30 AM, wb6bnq wrote: > Hi Dave, > > My question was more centered on determining your expectations. I ran > into an even worse condition with the cheap sound card, in my shop > computer, I used for the Frequency Monitoring Tests (FMT) ran by > Connie (K5CM). Being in a space with no temperature control at all, > the sound card had a 7.0 Hertz variation over a few minutes. Clearly, > it was a crystal going wild. > > As an experiment, I decided to rip out the crystal and replace it with > the output of a HF synthesizer dialed to the proper frequency. My > synthesizer, and other LAB equipment, is locked to my house standard > which is monitored (not controlled by) with GPS. > > As expected, the results were spectacular ! I ended up with a > measurement process that had a resolution of 120ns, and maybe somewhat > less. At 1000 Hertz that is an uncertainty of +/- 1.2e-10. I did not > try to account for ground loops or other anomalies; and the sound card > was some cheap $18 item with no spectacular ratings in and of itself. > > I am now finishing up on a project to replace my expensive commercial > synthesizer so it can return to test equipment duty. If you are > interested in what I am doing in that regard, email me about it off list. > > As for the TS-2000 radio, I have not studied it, per se. But like a > lot of these modern radios there are several possible error points > within their design that could cause offsets and drift that may affect > the outcome depending upon your application. > > However, if you are using a common analog detection type radio in the > "AM" mode, then the radio does not matter to the outcome. The radio > only serves as a mixer, albeit an expensive one. For example, when > comparing an approximate 10 MHz unknown signal, the mixing action > provides four (4) more decades of resolution if the output of the mix > is 1000 Hertz. If using a modern DSP radio in the "AM" mode you may > have to account for possible slight errors in the internal codecs > (A>D/D>A). > > The only two error points that matter (using "AM" in the above > example) is the local signal generator used to beat against the > unknown incoming signal and the computer's sound card stability. If > both are tied to your "House Standard," then it is totally up to the > quality of your local standard's stability and accuracy. There are dirt cheap DDS-modules to buy from China, based on AD DDS-chip. If you need help with the reference frequency, you might want to use that TAPR module for clock-stepup. I don't think the TAPR module does the frequency you want straight away.
Just to give you some ideas to follow up. It will be much cheaper and compact than your RF-generator today, and considering you already is listening to a stepped down signal, the purity is good enough for the purpose. Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.