[time-nuts] VNA design

[Dr. David Kirkby]

On 3 June 2014 19:22, paul swed <paulswedb at gmail.com> wrote:
> Great comment by Dave on the fact that someone
> will give out some of the old options. Now I have to figure out what on
> earth that might actually mean.
> Regards
> Paul
> WB8TSL

There are a few options for those VNAs. These are basically generic,
but check your manual for more details.

1) Option 006, on an 8753B or later, allows the instrument to work to
6 GHz. It basically lets the receiver tune to 6 GHz, but the internal
source still only goes to 3 GHz. So you need an S-parameter test set
with a doubler to get to 6 GHz. But there is no harm in having the
option, irrespective of whether you have a 6 GHz test set.

2) Option 010 is the time domain. It converts the frequency domain
data to the time domain via an inverse FFT. Then you can put a "gate"
around some stuff in the time domain and transform that back to the
frequency domain.

A nice option to have, and very expensive on new instruments.

3) Option 002 allow the instrument to work on harmonics. I'm not sure
how useful that actually is - I think it was mainly for internal use
at HP, and is not of great use, but if you can get the option, you
might as well.

4) Old 8720 series instruments had a tuning step of 100 kHz. There is
an option to make that 1 Hz. How the **** HP got away with selling a
VNA where the step size was 100 kHz I will never know, but they did.

There are other options for the instruments - the most time-nut
related is the high stability oscillator. That is option 1D5 on my
instrument (8720D). I don't know how easy it is to add the hardware to
an 8753 - I suspect it is just one of the standard 10811A or similar
oscillators. If you do that, it would seem sensible to get the
instrument to report it has the option, even though it wont actually
effect the performance. It would affect the resale value, and would
mean Agilent would calibrate it properly if sent it for cal.

When my 8720D was sent it for calibration, the accuracy of both the
standard and the high stability oscillator was checked. Both were in
spec. I suspect they would not check the high stability one unless the
instrument reported it had that option fitted.


BTW, Agilent will still calibrate 8753s, and when I got my 8720D done,
it was not that expensive. I guess it is all relative, but the 8720D
is quite an expensive instrument, and I use it professionally, so it
is worth getting calibrated - unlike 99% of the other stuff I have.

Dave