I just got one of these modules on a board. It seems to work with u-center and Lady Heather. I'm still reading through the documents that I downloaded, but my understanding is that this module is essentially a mini-GPSDO, with a reference output of 30.72 MHz that is frequency locked to GPS. The internal TCXO is also supposed to be locked to GPS, eliminating sawtooth jitter. There was a previous GPSDO that locked it's internal oscillator to GPS, but I forget which one it was.
BTW, that oddball frequency is used for certain cellular systems. It has something to do with audio modulation. In fact, you can divide it down nicely for 96 KHz, 32-bit, 2-channel audio. I guess if you're an audiofool, you could GPS lock your stereo
In u-center, it seems to work very much like an M8T. One curious thing, when I set the TP2 to various frequencies, the ones that look stable, without lots of jitter are the same frequencies that are integer divisors of 24 MHz, not 30.72 MHz. The maximum TP2 frequency I can set is 24 MHz. So, is the M8F using the same TCXO as the M8T, and somehow still locking that oddball 30.72 MHz to GPS? I'm confused.
In LH, the M8F looks pretty much like an M8T. However, the device name is shown as "Ublox timing", and not a specific module. The sawtooth error shows as exactly 0.000000 nS. The accuracy is exactly 6.000000 ns (it started out as something over 1000, then dropped to 9 ns, then 6 ns). It just went up to 8 ns, then dropped to 7 ns (I'm indoors, so perhaps that's why it's jumping). Since LH reports sawtooth error from other u-blox receivers, can I assume that this M8F actually has no sawtooth error?
One anomaly regarding the reference output: it's supposed to be 30.72 MHz, but I'm reading 32-34 MHz, and it's not stable.Does anyone have experience with the M8F, and can provide some insight? I'll continue to read the documentation.
The M8F is also supposed to allow disciplining an external oscillator, with the addition of an external I2C DAC. This is the reason I got this module. If it works, this should make a dandy GPSDO with an external 10 MHz OCXO.