Electronics > Metrology

GNSS RB (chinese)

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Johnny B Good:

--- Quote from: testpoint1 on February 10, 2022, 10:01:58 pm ---Hi, you need to know which Rubidium clock inside, and, my selling the Rubidium Clock that combined the GPS, I am in US:

--- End quote ---

 Yes, I know where you're located. You sold me an Efratom LPRO-101 a year ago last August.  :)

EDIT: I've attached some photographs showing that LPRO I'd purchased from you.

 The first shows it perched on top of the 1/4 inch thick alloy heatsink plate resting on top of what I'd originally thought would be a most suitable enclosure.

 The second shows it resting on the heatsink plate, revealing my initial test measurements noted in black marker on the top cover.

 The third demonstrates how woefully inadequate my initial choice of enclosure had been - it's perched on top of the custom built case that it's now destined to be installed into.

 The fourth shows the LPRO wrapped in its initial 20mm thick polystyrene jacket still dwarfed by the more adequately sized enclosure - there'll be another 25mm thick wrapping of insulation plus 10mm polystyrene panels glued to the inner walls of the enclosure to prevent the warm/hot exhaust from heating up the enclosure itself.

 The enclosure is going to be used to couple changes of room temperature to a sensor, the output of which currently sets the fan speed to match cooling demand and minimise over/undershoot and eventually allow me to compensate for their biasing effect on the base plate heatsink's temperature control.

 Incidentally, the traces on the DSO are showing a 2MHz Sinc pulse from my modified FY6600 locked to the 10MHz GPSDO reference and the 10MHz output from the LPRO which is the trigger source. That had been my initial attempt to keep track of overnight phase drift due to leaving the LPRO "Hanging in the breeze". ::)

Johnny B Good:
Hello all!

 I've noticed that the attached images in my previous post did manage to attract some attention. The project is still a work in progress but in view of the interest shown, I thought I'd post a couple more images showing the more or less finalised assembly to satisfy curiosity as to its final incarnation.

 I've had it assembled and running for the past three weeks or so but I've been rather pre-occupied with refining the code that controls the temperature regulation and compensates for the effect of ambient temperature on cooling demand as well as the minuscule effect of barometric pressure variations (~ +8E-14/hPa) to even consider posting an update on my efforts so far.

 However, I've been itching to make some token effort at providing a brief update on my progress, hence the couple of attached images of the (almost) completed project.

 The project is "almost complete" since I'd like to wire the "Lamp voltage" and VCXO EFC monitor pins to a rear panel mounted 3.5mm stereo jack and possibly do the same for the calibration tuning voltage and the 5v regulator dedicated to supplying a thermally stabilised bias voltage for critically sensitive circuit elements such as the calibration pot and the ADC reference pin on the nano mcu and maybe even use it to power an add on buffer to prevent the current ripple noise on the mcu's 5v power rail from polluting the PWM outputs.

 However, this last item is going to require a mark II controller board since I've pretty well crammed as many components onto the current circuit board as I possibly can.  :palm:

 I've given the images descriptive names. The full view shows the 'scope traces of the GPSDO and RFS with infinite persistence (GPSDO is the trigger source) and the GPSDO's EFC voltage (SDM3065X) in the background.

 I do plan to post a full article on the project... eventually. I'm afraid you'll just have to make do with this mini-update and these attached photos for the time being.

Johnny B Good:
I've picked out some more photographs (19 in all so another post to follow this one) to show the transition from bare box with a polystyrene foam insulated LPRO simply plonked inside to the (essentially) "finished project".

 I finally decided to rebuild a redesigned polystyrene 'overcoat' using 25mm thick foam (the original had been a bit of a bodge using 20mm thick foam and needed some improvement to better accommodate the nano mcu board I'd piggybacked onto the DC jack with SMA adaptor board that testpoint1 had added to the LPRO).

 The pictures should give you an idea of the ventilation pathways which were designed specifically to minimise passive convective cooling (the heatsink fins are orientated horizontally to help meet this goal). The inspiration for this being the almost non existent convective cooling of FeelTech's (in)famous FY6600 AWG  >:D

 The final seven picture sequence shows the run up from initial power on  through to reaching the target base plate temperature state. The bi-colour status LED shows red until "atomic lock" has been achieved, at which point it changes to green. Reaching the target base plate temperature typically requires another 15 to 20 minutes. It then takes another 12 to 24 hours to reach ultimate stability somewhere in the region of 1E-12 to 3E-13 beyond which, a daily ageing rate in the region of 1E-13  begins to make its presence known. :(

Johnny B Good:
Here are the remaining 9 photographs:-


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