[time-nuts] HP 5334 oscillator performance

[Rick Karlquist]

I was the project manager of the 5334B, which was a reduced
factory cost replacement for the 5334A.  Of course I thoroughly
evaluated the 5334A before deciding what changes to make.  I will
apologize on behalf of the company for that oscillator
in the 34A.  It is a really poor design.  Giving the 5334A project
team the benefit of the doubt, I guess the philosophy was that
the built in oscillator is for very non-critical applications and
they didn't want to increase the cost to those users but putting
a decent oscillator in the standard counter.  Many users were like
us and had a house frequency standard, so we never used a built in
oscillator in a counter.  Due to time and cost pressures, we unfortunately
inherited the same oscillator in the 5334B.

So in both products, please plan on getting a 10811 or using an
external frequency reference.

Rick Karlquist N6RK
Project manager, 5334B, circa 1986



Colin Bradley wrote:
> I recently took one of my 5334A’s off of the house standard to lend to a
> friend. I thought it a good idea to check the onboard oscillator before
> lending it out. Both of my 5334A’s lack Opt 10 oscillators. This
> particular unit was almost 40Hz high in frequency. I tried to set it to
> frequency and had trouble getting it closer than 2Hz. The set-ability was
> very poor. I checked the service manual and found that HP only specified a
> final frequency within 8Hz. I can now see why. I then turned the
> instrument off for 12 hours. The next day I powered the unit back up. The
> oscillator was 20Hz higher than where I had measured it at shutdown the
> night before. It took well over an hour for it to re-stabilize and
> overshot the previous set point by 2Hz. At this point I decided to lend a
> Heathkit IM-2420 to the friend and continued experiments with the 5334A.
>
> I now took the second 5334A down and ran the same tests on it. This
> instrument was somewhat better but still shared many of the problems the
> first unit.
> 1)                  60+ minutes to stabilize after power-up. Oscillators
> would start out 9 – 19Hz high and settle in at +- 1Hz.
> 2)                  Poor retrace at turn on. Final settling frequency can
> vary by 1Hz.
> 3)                  Poor set-ability due to the ceramic trimmer.
> 4)                  Oscillator pulling of 2 – 3Hz when I connected another
> counter to the rear panel oscillator jack. The oscillator buffer is on the
> same ECL chip as the oscillator.
> After looking at the circuit I decided that a new TCXO would be a better
> solution than trying to modify the existing circuit for better
> performance. Since these units are used at room temp most of the time, I
> need not worry about a wide temp range specification.
>
> I set the following goals for the replacement oscillator.
> 1)                  Improvement of stability by an order of magnitude and
> set-ability of two orders of magnitude.
> 2)                  Replacement to be built on a circuit board that would
> mount in the oven oscillator connector on the main circuit board.
> 3)                  Use of the full time 24vdc at this connector to power
> the oscillator at all times. Use of an on-card battery supply for
> oscillator backup.
> 4)                  Cheap
> 5)                  Use of readily available TCXO oscillator module. After
> checking Mouser and Digi-Key I settled on a Mouser supplied FOX801BE 10mHz
> unit @ $13.46. to start my experiments. This oscillator draws only 2ma.
> and frequency is set by an external trim pot.
>
> I would be interested in the experiences of others with respect to the
> performance of their non-oven 5334’s (or 5328’s) and ideas that support
> the design goals. Thanks
> Colin
>
>
>
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