Didn't some of the 5345 or 5328 manuals have schematics for the 10544. I
have no idea if it's in the on-line manuals but I recall seeing the
timebases in some.
Phil
----- Original Message -----
From: "Bruce Griffiths" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Friday, January 15, 2010 4:39 PM
Subject: Re: [time-nuts] HP 10544A with dodgy output?
Nick
The 10544A had at least 2 variants.
I have the originals but the various datasheets are available on Didiers
site.
The earlier versions had a somewhat higher phase noise spec, as can be
seen from the datasheets with different dates.
There was a significant change to the circuit to achieve the lower phase
noise.
I don't have any details but I believe the changes were mainly to the
oscillator and the method of extracting the output signal from the
oscillator.
I suspect that using 2N3904's rather than a CA3045 may lower the close in
phase noise.
But this would depend on if the CA3045 were used in the oscillator.
Do you have the serial number of your 10544?
The circuit could be radically different as the CA3045 includes a
differential pair (the emitters of the pair are tied together).
From the image it appears that at least one of the transistors of the
differential pair is used in the circuit.
Is the board shown actually the oscillator board or just the buffer board?
Is your OCXO a 10554 or is it a 10544A?
Bruce
Nick Foster wrote:
Bruce,
The 10544 I have doesn't correspond to the 10544 schematic I found on
leapsecond.com. Here's a photo of the AGC board inside mine:
http://www.nerdnetworks.org/~bistromath/photos/misc/10544.JPG
It's an RCA CA3045 array instead of the 3094's used in the schematic I
saw. Looks like the best thing to do is pull it out and test it, and
replace if necessary. I imagine that despite the transistor change the
schematic is mostly the same. Do you happen to know for sure?
Thanks,
Nick
Date: Sat, 16 Jan 2010 09:35:03 +1300
From: [email protected]
To: [email protected]
Subject: Re: [time-nuts] HP 10544A with dodgy output?
The output of the diode detector is compared with the dc base voltage of
the oscillator transistor adjusting the oscillator transitor current
whenever the detector output deviates from
Oscillator transistor base voltage - 2*Vbe.
Bruce
Nick Foster wrote:
Thanks for the quick reply, John.
From: [email protected]
Okay, 12V on the oscillator (pin 3) and 20V on the oven (pin 14). How
much
on the oven controller, pin 8?
+12V. The oscillator uses the same supply as the filter, with the
addition of a 10mH inductor + decoupling caps.
Are pins 2, 4, 5, 9, and 15 grounded? Pin 6 (EFC) should be grounded
for
initial testing.
Yes and yes.
Upon looking further, something jumped out at me: the output is 2.2V
RMS into 1000 ohms instead of the 1V RMS spec'ed in the datasheet. So I
suppose the problem might be in the AGC circuitry, instead of the
output emitter follower. It doesn't look as though the AGC in this
oscillator contains a trimpot, like the 10811 does.
I'm using the schematic at
http://www.leapsecond.com/museum/10544/10544-3.gif, but I don't have a
good idea of how that AGC works.
--n
From: [email protected]
To: [email protected]
Date: Fri, 15 Jan 2010 15:06:42 -0500
Subject: Re: [time-nuts] HP 10544A with dodgy output?
Okay, 12V on the oscillator (pin 3) and 20V on the oven (pin 14). How
much
on the oven controller, pin 8?
Are pins 2, 4, 5, 9, and 15 grounded? Pin 6 (EFC) should be grounded
for
initial testing.
John WA4WDL
--------------------------------------------------
From: "Nick Foster"<[email protected]>
Sent: Friday, January 15, 2010 2:53 PM
To:<[email protected]>
Subject: [time-nuts] HP 10544A with dodgy output?
Hi all,
I've just built a GPS-disciplined oscillator built around a 10544A,
somewhat in the style of the Brooks Shera unit, just to use around
the
shack. Problem is, now that it's wired up, I notice the output is
heavily
distorted. It's clipped on the negative side of the waveform, like an
emitter follower without enough headroom. The more I load the
oscillator
output, the heavier the clipping. When I load the oscillator output
with
1000 ohms, spec for this unit, almost 30% of the waveform is clipped
on
the negative side. If I don't load it at all and just put a probe on
the
output, it looks OK, but still some flattening of the bottom half of
the
waveform.
I've got it wired up according to the datasheet, with +12V on the
oscillator and +20V on the heater. The grounds for the
oscillator/amplifier, oven controller, heater, and output are all
tied
together.
I know these are old units, and I'm wondering if this is a problem
(for
instance in the output emitter follower amp) that others know about,
before I tear into it looking for a solution.
Thanks for your time,
Nick
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