[time-nuts] Can a VNA be a high resolution frequency counter

[Azelio Boriani]

The frequency accuracy is related to the conversion process, the sampling
process and the computation that follows. In a sampling VNA the frequency
is extracted after the FFT, I suppose, so I don't think that sampling VNAs
can do any better than a real frequency counter. Sweeping spectrum
analyzers seems to stop for some time the sweep at the marker and route the
IF to a real counter, when the counter is called in: this should be more
accurate.

On Wed, Nov 14, 2012 at 3:30 AM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> The help file is correct, but possibly a bit misleading. Most of what they
> show could be done by a computing counter. They have been around long
> enough that they are a sub $100 ($50?) item these days. Clock jitter is
> going to be a very real limit doing what they are trying to do.
>
> Bpb
>
> On Nov 13, 2012, at 8:27 PM, Malcolm <g0mic at aol.com> wrote:
>
> > I have been looking at the DG8SAQ VNA for other purposes and it is
> suggested in the VNWA_Help.pdf  on page 158 that it can be used as a high
> accuracy / resolution counter. Document available at
> http://www.sdr-kits.net/vnwasoftware/?20    .
> >
> > Ignoring any drift in the TXCO as I would drive it from an external
> reference source ( GPSDO or Rb derived) of 36 MHz,  being a (junior in
> knowledge) time nut I added this as another reason to buy the VNA.
>  However, I do have some reservations and would like the comments of better
> qualified time nuts and the answers to some questions:-
> >
> > 1.  Can the VNA really have that level of resolution?
> >
> > 2.   Is the resolution  reduced in the ratio of the measured frequency
> to the clock frequency e.g. at 360 MHz is the resolution 10 times worse
> than that at 36 MHz?
> >
> > 3.   Are there any other factors that should be taken into account when
> performing frequency measurement please?
> >
> > Whether or not  this feature works is not a deciding factor in my
> consideration just a possible plus.
> >
> > Your comments please ladies and gentlemen.
> >
> > Regards
> >
> > Malcolm
> > G0MIC
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