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 _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.