[time-nuts] Re: HP 8663A: option 003

[alan bain]

On Sat, 22 Apr 2023 at 22:39, John Miles via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> > HP 8663A option 003 gives guaranteed/specified SSB performance for the
> > 640 MHz output. What exactly does this mean? Are there hardware
> > differences in the reference section of the 003 units in comparison with
> > non-003 units? Or, was the hardware the same and HP simply categorized
> > them according to measured SSB performance? If it's the latter, what
> > implications does this have for buying 003 or non-003 units now? I think
> > I remember reading somewhere on this list that 10811A SSB
> > categorizations don't matter much after this amount of aging. Maybe the
> > same thing applies here?
>
> Option 003 was aimed at customers who needed to use the synthesizer with a 3048A system equipped with an 11729B/C downconverter.  AFAIK all of them had 640 MHz available on an SMC jack under the top cover, but it seems that only the -003 units brought it out to the rear panel.

I seem to vaguely recollect Opt 003 also provided external EFC to the
timebase reference to allow the phase of that 640MHz signal to be
tweaked until in quadrature for phase noise measuring purposes.
Although I am always amused by the fact that for checking the SSB PN
of the 640MHz signal one needs another 8662 whose PN on the 640MHz
output is known. This feels very Alice in Wonderland.

> Many of the 8662As were built without the rear-panel jack, but it can be added easily enough.  I've never seen an 8663A that didn't have it.
All of mine don't have it, but at least there's a blanking plug, not a
need for a new rear panel (as with moving from front to rear inputs on
some HP products).

I'm assuming that in fact the PN measurement is of the incoherent sum
of the reference and DUT PN and what really matters is having the ref
PN as low as possible so that the measurement provides a tight upper
bound (possibly they even go as far as to assume 50-50 split of noise
power between generators?). But I'd be very interested to know if
there is more to it than that.  The manual also suggests that really
using a 3047 would make this measurement much easier and since this
would seem to be the reason for owning an opt 003 why not.

Which brings me to the question of the interfaces (I have none of
them, but do have two 8662s and would be interested in making some PN
measurements). The 3047 used the spectrum analyser interface 35601A
which I know almost nothing about and the 3048 used the 11848A for
baseband or 11729B/C for mixed down measurements. Are they all equally
useful today, possibly with a more modern FFT analyser as some of
those HP dynamic signal analysers have very low numbers of bits in the
ADC even compared to a soundcard!

Alan




>
> Whether a given unit met the PN requirements for option 003 depended on not only the 10811 OCXO but on the rest of the reference multiplier chain as well, including the 40 and 160 MHz crystal filters.  It's unlikely that all of them met the spec, given how tight the 100 Hz limit is in particular.  So there would have been some selection involved at the factory.  It might have come down to something as banal as fan blade balance.
>
> With regard to the SAW oscillator, none of the 8662/8663 generators included one.  But if you didn't have option 003 -- or if you didn't have an 8662/8663 at all -- the SAW filter stage at the 640 MHz input on the 11729B/C could be configured as a standalone oscillator.  The filter was necessary in any case because the 640 MHz output from the generator was full of spurs from the other stages of the reference multiplier chain.
>
> -- john
>
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