[time-nuts] Just any counter external reference and discipline mode.

[Richard (Rick) Karlquist]

> There's a lot of lore out there that, for instance, HP would put 
> oscillators with good long term stability in counters, but for things 
> like a spectrum analyzer or signal generator, you'd use an oscillator 
> with good close in phase noise, because absolute frequency accuracy 
> isn't as important, but ability to make close in measurements with high 
> dynamic range is.

Yes, some validity to that.  Santa Clara Division's overriding 
constraint was to make sure that every oscillator could find a home.
The counters were synergistic with the RF instruments in that sense.
Another issue was that they didn't want to use a lot of resources
to do production testing.  Finally, as a captive supplier, SCD
was not allowed to charge extra $ for specially selected oscillators.

> 
> I would also not make any assumptions about continuity of design, 
> especially when it changes from an all analog to a DDS based design. A 
> synthesizer using analog synthesis with PLLs would smoothly sweep, while 
> a DDS design typically goes in discrete steps (unless specifically 
> designed for smooth sweeps), and may or may not be phase continuous 
> across steps.
> 

There are a lot of quirks about continuity of design.  In general,
the microwave divisions in Santa Rosa wanted to keep the "platform"
and architecture the same and update products by making newer
blocks that did the same function as older ones.  Then there was
the permanent magnet YIG tuned oscillator (PMYTO) ("because we can" 
since we make our own YTO's).  This kept showing up in new products long
past its "best by" date.  A fixed frequency 2nd LO using a microwave
cavity for the tank circuit initially used in 1968 was still being
designed in in the 2000's.  The YTO kind of spoiled HP with its
effortless smooth phase continuous sweeps.

Around 2000, when I was working for Agilent Labs, I got assigned to
a committee to study replacements for the YTO.  The problem was
that they wanted a drop in replacement, rather than a new architecture
that was not designed around the YTO.  I was happy to be paid to
attend meetings, but in the end I don't think we accomplished
anything.  We didn't even kill off the PMYTO of all things.
There is a lot of inertia, especially when people's jobs depend
on nothing changing.

Rick N6RK