The way I look at short term stability is to multiply up to microwave frequencies then mix the two and look at the resulting beat note. The popular ADF4351 Fract-N synthesizer is ideal for this. Take two of them, and programme for two frequencies in the GHz region a 1kHz or so apart when driven by the two 10MHz freqs that are being compared Apply the two multiplied signals to a mixer, and look at the resulting IF product with a PC soundcard input. Using spectral analysis software with a waterfall display, such as Spectran or Spectrum Lab you can look at the multiplied frequency instability in real time.
An example of the techniques used on a range of 10MHz reference sources can be found here (I used a different Fract-N synth with a smaller setting grid possible than teh ADF4351 can give, but the same idea applies) Andy www.g4jnt.com On Sun, 28 Nov 2021 at 18:19, Erik Kaashoek <[email protected]> wrote: > As the collection of frequency sources and counters in my home lab is > growing I'd like to understand the performance of the frequency sources. > Two different GPSDO do help to check long term stability. > But the Rubidium frequency standard I have (Accubeat AR60A) is fairly > unknown and seemingly not of good reputation, more specifically its > (very) short term stability is doubted. > So how best to check very short term (below 1s) frequency stability. > The frequency counters available loose resolution quickly when the gate > time is reduced below 1 second and high performance phase noise > measurement equipment is not available so google helped with a search > for alternative measurement methods. > What I found was a method using two frequency sources, one of the two > being a VCO, a mixer and some filters and amplifiers. > By weak locking (large time constant) the VCO source using the mixer as > phase detector to the other source, the output of the mixer's IF port > should carry a voltage real time proportionally to the phase difference > and by filtering and amplifying it should be possible to check for > variations in the 1ms-1s range. > Maybe even a scope can see the variations. > When you know the amplification and the full range voltage you can even > do an absolute measurement. > Would this method work? > Any specific concerns to take note of when doing the measurement? > Removing the DC component (or locking the VCO such that there is no DC > component) will be crucial I guess but given the slow speed of the loop > even an ADC->computer->DAC->VCO setup can work. > Any suggestion is welcome. > Erik. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
