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

[Richard (Rick) Karlquist]

Good question; answer is not so simple.  Here goes:

Signal generators and spectrum analyzers have to have a low phase
noise oscillator inside to be able to generate/detect spectrally
pure signals.  Unlike counters, the 10811, etc has to be standard
equipment, not an option.

Therefore, in order to make the product "customer proof"
(or "sailor proof" if the Navy is the customer), they
do not allow the customer to supply has own noisy external
reference.  Instead, they lock the high quality internal
reference to the customer's external reference ... with a
VERY SLOW phase locked loop.

An additional insurance policy that goes along with this is
that this scheme limits how far off of 10 MHz the external
reference can go.  The internal workings of the product
may include PLVCXO's etc that don't have much frequency
agility, such as the optional 640 MHz SAW oscillator in
the 8662A.

Now for something completely different:

Counters, OTOH, ship with an oscillator that is basically
a 99 cent clock oscillator like your computer has.  There
are many applications where all you need is what we call
"indication only" (AKA sanity check) where this cheap
oscillator is fine.  The other end of the spectrum was
exemplified by the HP Santa Clara Division itself.  We
had a high performance HP Cs standard compared to Loran
or later GPS that was distributed around the plant.
We would plug this external reference into the counter
and make 12 digit measurements.  Spectral purity wasn't
so critical for a counter, just to get the frequency
right.  Also, the counter worked perfectly well if
you put in 10.001 MHz etc, it just scaled everything.
There were various reasons why you might want to do this.
Customers without a house standard, but with high
accuracy demands had to pony up the $ for the OCXO
option.

IMHO, this "different strokes for different folks" made
a lot of sense.  Also, each division was autonomous, so
there was no way to force all the divisions to do
external reference one "corporate" way.  That wasn't
what the "HP way" was about.


On 7/13/2020 9:58 AM, Taka Kamiya via time-nuts wrote:
> I'm sorry to interject a newbie question....  I changed the title to distinguish from rest of the conversation.
> 
> At least for me, the general public, circuit diagram is not made available for later models.  I have no way to tell for sure what is being done inside.
> 
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>   
> 


Before I got a job at HP in 1979, the manuals did have circuit
diagrams.  I used to read them like text books.  I would
often open up HP instruments to discover details not
covered in the manual.  I reverse engineered them, and
even modified them.  Another good resource was HP Journal.

That is what inspired me to apply for a job there.
Once there, I could talk to the actual engineer
who designed the thing.  Amazing!

Also, at HP, I discovered why the screws always
cammed out:  "Pozidrive".  Never heard of it before.
Who knew?

Rick N6RK