[GPS_Standard] Ovenaire OSC 49-61C

[Geoff Blake]

On Wed, 23 Jan 2008, Bert, VE2ZAZ wrote:

> Hi (again) Geoff,
>
> It may not be visible on the GPS_Standard article pictures, but I use the
> same Ovenaire OSC 49-61C OCXO in my system. I don't have the specs. So I did
> a bit of experimenting to find out the pinout, the voltages, the tuning,
> etc. This unit has no electronic tuning pin so I added one. The final unit
> works well and meets the my GPS_Standard system specs. That being said, The
> HP 10811 and HP10544 series are probably better units. I have not personally
> tried to compare; just a gut feeling. Note that the Ovenaire is a
> single-oven unit.
>
> I had to crack open the unit in order to figure out what the pinout was. I
> also added a EFC (electronic tuning) line to the unused pin. I basically
> connected that line to the center wiper of the fine tuning potentiometer. I
> then adjusted the pot for a 1Hz end to end tuning range with 0-5Vdc applied.
>
> I found what the supply voltages were by slowly increasing the voltage until
> the unit worked solid. This is how I wired it:
>
> Pin1: GND
> Pin2: GND
> Pin3: +8V DC (oscillator)
> Pin4: No Connect, re-wired for EFC, 0 to +5V DC
> Pin 5: +15V DC (oven)
> Pin 6: GND (oven)
>
> By the way, when I opened the unit the insulation fell off in powder,
> completely dried out. I replaced it with some pink bubble pad, the ESD-free
> pink type. I cut several pieces and enveloped the electronics. I re-inserted
> everything in the case.
>
> There you have it. Have fun experimenting!

Hi Bert, List,

Right, I have studied the 8568A circuit diagrams and it
appears that there is no information given rergarding pin
connections.

I have found the supply circuitry and basically the 8568A uses a
diode gate arrangement to switch the power rails (oven and osc.)
between the normal (+20v) supply and the "standby" supply (which
is regulated at ~20V).

Because of the diode gate, the oven supply is one diode drop below
+20V.

The supply to the oscillator (but not the oven) is switched off
via a series transistor when an external standard is used so the
oscillator supply is a Vce(sat)) below that of the oven.

There is also an "on temperature" tellback from the oven which I
have not investigated thus far.

Because the OSC 49-61C has no EFT facility, I am going on the hunt
for another 10811 and will probably consign the Ovenaire unit to a
stand-alone (not GPSDO) standard.

Thanks & 73
Geoff

-- 
    Geoff Blake G8GNZ      located  near  Chelmsford,  Essex,  U.K.
    Please reply to:      geoff(at)palaemon(dot)demon(dot)co(dot)uk
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