I've read about a zillion pages on the FY6XXX. Still not clear on the connectors on the back. Any chance one of those connectors will accept a 10 MHz reference input signal?
No chance of that. They're all accounted for in the manual. However, don't let that stop you fitting another socket (BNC or an SMA-F) and following in Arthur Dent's footsteps, linked to below (or mine when I finally get round to adding an SMA-F socket to complement my version of Arthur's OCXO upgrade).
https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1346454/#msg1346454 Since I chose to modify the existing PSU board (
https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg2310768/#msg2310768) rather than replace it, I had to add the innards of a small 12v 300mA smpsu wallwart to power my own OCXO upgrade. This gave me the advantage over Arthur's setup in that I could wire this directly to the C6 mains socket I'd fitted to overcome the ESD risk posed to any DUT so I could turn the generator off on the rear panel switch and keep the OCXO running whilst the unit remained plugged into a live mains outlet.
Using the the front panel "Standby" button only turns the display off by way of a power saving of circa 1 or 2 watts at most, leaving it to consume some 5 watts or so. The consumption of the OCXO once up to temperature is a mere 1.35W from the mains (the OCXO itself only consumes some 700mW naked or around 600mW when blanketed with quarter inch thick rubber foam - primarily to buffer it against random wind chill effects from the cooling fan).
I'm planning on avoiding the issues of using a switch to select between the internal and external frequency references by using the "Injection Locking" technique whereby the external reference is used to couple remarkably little, yet more than ample, energy into the local OCXO to cause it to lock to the external reference automatically without the need for a change over switch.
I've already proved that the 10MHz CQE OCXOs I'm using can be locked over a +/-10ppb range quite readily via their output pins which, since an error of as much as 1ppb can now be regarded as outrageously off frequency, is a more than ample lock in range (I've been able to trim to within 50ppt of my basic fledgling GPSDO[1] and see the OCXO in my FY6600 stay within +/- 70ppt for a week or more making long term calibration to within 0.5ppb a realistic goal).
[1] I've been experimenting with GPS modules for several months now and only recently acquired a collection of OCXOs to develop the original raw 10MHz PPS output calibration standard into a proper, if rather basic[2], GPSDO. Currently I have it assembled onto a prototyping board which I've been tinkering with for more weeks than was strictly necessary.
I finally shut it, the 'scope and the FY6600 down just a few days ago to get used to the idea of not being able to glance at the 'scope trace evidence of my successes with the FY6600 OCXO mod and the GPSDO project by well of self admiration at getting so close to boxing off my first homebrewed GPSDO project. It seems I'm finally ready to take that boxing off step since, surprisingly, I didn't feel any obvious symptoms of "Going Cold Turkey".
I guess the knowledge that the only way forward now to get away from the susceptibility to "Theremin Effect" induced phase shifts and other prototyping board layout induced instabilities, is to actually commit it all to a PCB fitted into a nice metal enclosure to shield it from external environmental influences.
Once I've sorted out the GPSDO, I'll be able to turn my attention back to the task of fitting an SMA-F external reference socket and injection locking circuitry into the FY6600. I'll take a bunch of photos to make a "Show and Tell" post in the FY6600 thread when I've completed this (final???) modification. It'll probably take me a few weeks to get to this stage so don't wait for this with bated breath.
[2] Basic in the sense that I'm just using a two pole RC LPF on the phase detector output which, whilst sufficient to suppress the jitter on frequencies that are derived using non-integer divide ratios of the 48MHz clock and deal with the sawtooth adjustments, does not have the long term averaging effect of a micro-controller filtering algorithm to filter out the basic GPS navigation system shortcomings in handling ionospheric variations which reflect as nanoseconds worth of phase shift (typically as much as +/-15ns over periods of 30 to 300 seconds and beyond) on the PPS signal (100KHz setting in the U-blox M8N (fake) module I'm currently using to phase lock my 10MHz OCXO to).
Whilst these phase variations don't fatally detract from the process of confirming that a free running OCXO or Rubidium clock is already within a few PPT of nominal, trying to make recalibration adjustments otoh, becomes rather a matter of 'dumb luck' and persistence when it comes to any attempt at trimming an OCXO to within 50ppt of frequency.
JBG