[time-nuts] Best phase detector / mixer for 100MHz?

[Garry Thorp]

Hello Anders,

I have used the Mini-Circuits ADE-1H as a combined mixer and phase comparator, to lock a pair of Pascall OCXOFs together and give an output at twice the frequency. With ~18-19dBm into the LO and RF ports, the output level at 2f (from the IF port) was ~11dBm. The mixer didn't appear to increase the phase noise floor noticeably, beyond the 3dB increase due to adding 2 oscillators together.

If you load the IF port with 50 ohms at RF and high impedance at DC / low frequency, you should get significantly more than 1V/radian sensitivity with 18dBm into each input. As the normalised close-in phase noise of 100MHz OCXOs is considerably higher than that achieved by the best 5-10MHz oscillators, I don't believe the mixer's flicker noise should be significant.

Garry Thorp


I have been using an minicircuits mixer as a phase detector for measuring low frequency(5-10MHz) and it is usually good enough. But when I want to measure 100MHz the sensitivity of the mixer decreases a lot, so when I want to measure some really low noise 100MHz(Pascall -178dBc floor with 18dBm out) oscillators the sensitivity is not good enough. I read in an old article by Walls, Stein et al(Design considerations in state-of-the-art signal processing and phase noise measurement system) that one can use two diodes in series in the double balanced mixer to increase the sensitivity. I tried this with some standard 1n5711 Schottky and the sensitivity is now 1V/rad, but is there a easier way to do this? /Anders