> It (LTSpice) has some severe limitations for most of the simulations I have done.
You might bring those up with Mike Engelhardt (the author). He doesn't miss many tricks. > These need to be supplemented with on board filtering as they aren't > quite as quiet as you need. > Either the NIST style darlington buffered RC low pass filter (one per > amplifier) and/or a modified (stabilises the shunt transistor re by > making its collector current approximately PTAT) version of Wenzel's > active power supply noise filter can be used. The Jung article at Gerhard's link claims 3 nv/root-Hz at 1 kHz. Wenzel's page claims 20 nv/root-Hz at 1 kHz. What figures would be expected from the modified version you're talking about? > You can easily measure the phase noise for low offset frequencies using > a low noise mixer with appropriate (not 50 ohm) IF termination followed > by a low noise (audio frequency) preamp driving a sound card. A 24 bit > sound card is ideal, however 16 bit sound cards just need a little more > preamp gain. No need for a PLL just split the output of a low noise OCXO > or similar source drive the mixer LO port with one output and the > isolation amplifier with the other whilst the isolation amplifier output > drives the mixer RF port. You will need to adjust the phasing between > the LO and Rf signals so that they are approximately in quadrature by > using a suitable length of coax or other means. You can even take > advantage of the 2 channel (stereo) sound card inputs to do get well > below the mixer noise and/or sound card noise floor by using cross > correlation techniques. What's the current thinking re: FFT window functions for noise measurement? Does it matter what you use, as long as the window's equivalent noise bandwidth is factored in? -- john, KE5FX _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
