Salvaged OCXO by ar electronique
Hi,
I recently bougnt two used DVB modulators by Teamcast for salvaging
parts. There were a couple Mini Circuits VCOs, mixers and filters in
them as well as a 300Msps DAC and a beefy FPGA. But the most treasured
part for now is an OCXO (my first one!) labelled:
ar electronique micrOSTAR-FB 509 A 10 AR1275
My usual searching the list archives on time related parts didn't turn
anything up. I'm having a really hard time to find a data sheet for it.
A mail to the manufacturer remains unanswered. The closest I could come
to one is this Product matrix:
http://www.ec-m.it/docs/OCXO.pdf
This reveals some marketing specs and also that it is a 12V-supply-only
part, but no pinout or ratings.
I got the OCXO running by analyzing the PCB a bit, which is not that
easy because it appears to have infinite layers and I'm getting blinded
by the gold plating.
However, there is one pin left which measures open on the PCB and 8V
when leaving it unconnected. Maybe I'm supposed to buffer that? I also
still have no idea how regulated that single-supply must be or what load
it expects on the 10MHz output…
I'm having a hard time finding these answers myself since this is the
most stable oscillator in my shack by far and I can't really measure
what happens when wiggling the unknown PIN or the 12V, or changing the
load on the output. Any input appreciated!
regards,
Andreas
Hi
If you have not already spotted a Vref pin on the unit, your magic
8V pin may be the Vref for the EFC. It also could be “factory use only /
do not connect “.
There are OCXO’s on eBay in the < $30 range that should do about as
well as what the spec sheet shows for the part you have. The unanswerable
question is of course “which ones?”. As noted in many posts sorting
through this and that to find a good part is never easy.
Bob
On Apr 30, 2020, at 3:27 AM, Andreas Seltenreich seltenreich@gmx.de wrote:
Hi,
I recently bougnt two used DVB modulators by Teamcast for salvaging
parts. There were a couple Mini Circuits VCOs, mixers and filters in
them as well as a 300Msps DAC and a beefy FPGA. But the most treasured
part for now is an OCXO (my first one!) labelled:
ar electronique micrOSTAR-FB 509 A 10 AR1275
My usual searching the list archives on time related parts didn't turn
anything up. I'm having a really hard time to find a data sheet for it.
A mail to the manufacturer remains unanswered. The closest I could come
to one is this Product matrix:
http://www.ec-m.it/docs/OCXO.pdf
This reveals some marketing specs and also that it is a 12V-supply-only
part, but no pinout or ratings.
I got the OCXO running by analyzing the PCB a bit, which is not that
easy because it appears to have infinite layers and I'm getting blinded
by the gold plating.
However, there is one pin left which measures open on the PCB and 8V
when leaving it unconnected. Maybe I'm supposed to buffer that? I also
still have no idea how regulated that single-supply must be or what load
it expects on the 10MHz output…
I'm having a hard time finding these answers myself since this is the
most stable oscillator in my shack by far and I can't really measure
what happens when wiggling the unknown PIN or the 12V, or changing the
load on the output. Any input appreciated!
regards,
Andreas
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Bob kb8tq writes:
If you have not already spotted a Vref pin on the unit, your magic
8V pin may be the Vref for the EFC. It also could be “factory use only /
do not connect “.
Thanks - I think I did spot such a pin: there's 5.3V suspicuously close
to the tuning input, and wiring a pot to it with the wiper to tune
appears to do the right thing. I guess the 8V will have to remain a
mystery then…
Here is my current best guess in case someone else searches the archives
in the same situation:
+-------------------+
10 MHz sine | o o | 12V --,
1.3Vpp | | | connected to
| micrOSTAR-FB 509 | | supply on PCB
| (top view) | | 250mA…100mA
GND | o o | 12V --^
| |
| |
5V3 out | o |
TUNE | o o | Mystery 8V out, measures open on PCB
+-------------------+
There are OCXO’s on eBay in the < $30 range that should do about as
well as what the spec sheet shows for the part you have. The unanswerable
question is of course “which ones?”. As noted in many posts sorting
through this and that to find a good part is never easy.
I skimmed the archives in that regard before, but thought I'd get this
DVB-modulator instead - the same price but lots of extra RF critters
(and a too-large-to-be-useful machined aluminum case).
Thanks also for the off-list mail from Tim about what to expect from the
tuning pin. The entire unit actually had a 1PPS-input, but it went into
the FPGA on the digital board. The connections were
+----------+ +----------------+
| RF board | --10MHz--> | digital board | <-- SMA "1-pps"
| w/ OCXO | <---IF---- | w/ 300MHz DAC | <-- rs485
+----------+ +----------------+
rs485--^
So maybe the oven was not disciplined and the digital side just shifted
the IF around to compensate. Both had a PIC controller with a rs485
connection to the outside world though, so something external could have
talked to both and adjust a DAC to the oven, although I didn't spot a
discrete one on the PCB yet.
I don't have a frequency counter in the shack, so I improvised with my
HackRF (0.5ppm-TCXO). To take a closer look at its performance and
tuning it, I'm squaring the OCXO with a 74AC04 and look at a
high-resolution-FFT of the 200th overtone. The FFT-bins are 0.1Hz wide.
Here's a screenshot of the warmup. The screen is 190Hz wide (apparently
gqrx can't draw sensible axis labels for such a high resolution FFT)
http://aurora.npff.co/~andreas/ofen2.jpg (110kB)
I guess this is what the texbooks say a SC-cut warmup curve should look
like. The residual drift is probably the TCXO in the Hackrf: Touching
the HackRF causes dents in the curve while touching the oven doesn't
cause a visible change.
regards,
Andreas