[time-nuts] Racal 9420 OCXO

GandalfG8 at aol.com GandalfG8 at aol.com
Wed Aug 24 09:13:15 UTC 2011

In a message dated 24/08/2011 00:03:19 GMT Daylight Time,  
danrae at verizon.net writes:

Nigel, I  took the liberty of correcting the part number in the header.  
They  are quite common, also quite often go wrong, so beware if you buy 
any off  ebay...

I don't think Racal released circuit diagrams of any of their  ovens.  I 
have traced out the circuit of the rapid warm up oven found  in a lot of 
receivers, the 9442-12 and have fixed those, there is a  ceramic cap that 
frequently goes wonky.  The two 9420s I have fixed  were just broken 
wires; they seem to have used PVC insulated wire which  degrades...  I 
haven't done the homework on those yet.

The  9420s I have do have an EFC input as well as a stabilised Voltage 
out to  feed it, and in the receivers I have that use it [RA1795] the 
fine setting  is done from that, coarse setting from the top adjustment.

So yes, in  theory they could be used as a basis for a GPS disciplined 
standard, but a  quick eBay search shows a lot of more modern and 
probably better quality  10 MHz OCXOs from China...


Hi Dan, and thanks for the correction, bit of a silly error considering I  
actually had one in front of me as I typed:-)
I've never owned an RA1795 but don't recall the fine tune option being used 
 in the RA1794 or 1796, despite that table I included, but it's been a 
while  and I could be wrong.
This 9420 has a base plate still attached and with pins 5 and 6 linked at  
the B7G socket, which does seem to imply the EFC option could be available  
even if not used in this particular instance.
Thanks for the repair tips, I'll bear that in mind when I get time to  
check this one out.
I certainly agree re the more modern 10MHz oscillators, and I don't have a  
particular need for another 5 MHz GPSDO anyway, but having been  given this 
oscillator thought it might be fun to knock something  up and see how it 
compared to the Rapco 1804M units I've been playing  with.

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