[time-nuts] Measurement of Peak Frequency Using a Perseus SDR

[Magnus Danielson]

Hi Mark,

On 2019-01-09 08:27, Mark Goldberg wrote:
> I believe I finally have my frequency measurement process refined and have
> described it here:
>
> https://drive.google.com/open?id=1luVumTygkvfnDsZvGZGSsJA75IwMKmJ8
>
> Comments, corrections and criticism are welcome.

I have not seen anyone comment on this post yet.

It's an interesting approach and in general, this is one of the ways we 
can expect that frequency/stability measurements to be done these days, 
by sampling the RF and analyze it.

It would be interesting to figure out why you have a "bump" there, so I 
wonder what part does that.

For one thing, if the frequency estimation algorithm you depend on does 
averaging/least-square style of algorithms, the lower taus will be 
significantly lower than expected. TvB has some pretty good plots from 
experiments illustrating this.

Another thing, one reason to get a "bump" is due to high Q in a PLL circuit.

However, I'd be careful to judge it to be any of these without more 
careful look on the data.

It can be useful to alternate views to figure things out. For instance, 
swapping between MDEV and TDEV could give you some hints. Similarly 
swapping between frequency and phase does the same in raw-data view.

For phase/frequency plots, it may be worthwhile to average the data 
using the +/- keys in TimeLab, as the filtering away high-frequency 
noise may make it easier to see lower-frequency variations.

In general, I recommend you to have a third reference to play around 
with and measure. As one fools around with different combinations one 
learns to see which artefacts follows which device.

Do keep up the investigations. Try different approaches and learn.

Cheers,
Magnus