# Re: [time-nuts] Question about frequency counter testing

```Hi, Magnus!

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From: "Magnus Danielson" <mag...@rubidium.dyndns.org>
```
```2. Study how PDEV calculation fits on the used HW. If it is possible to
do in real time PDEV option can be added.
```
```
You build two sums C and D, one is the phase-samples and the other is
phase-samples scaled with their index n in the block. From this you can
then using the formulas I provided calculate the least-square phase and
frequency, and using the least square frequency measures you can do
PDEV. The up-front processing is thus cheap, and there is meathods to
combine measurement blocks into longer measurement blocks, thus
decimation, using relatively simple linear processing on the block sums
C and D, with their respective lengths. The end result is that you can
very cheaply decimate data in HW/FW and then extend the properties to
arbitrary long observation intervals using cheap software processing and
create unbiased least square measurements this way. Once the linear
algebra of least square processing has vanished in a puff of logic, it
is fairly simple processing with very little memory requirements at
hand. For multi-tau, you can reach O(N log N) type of processing rather
than O(N^2), which is pretty cool.
```
```
```
I had some free time today to study the document you suggested and do some experiments in matlab - it was very useful reading and experiments, thanks! It looks like the proposed method of decimation can be efficiently realized on the current HW. Also as a side effect calculating large averaging in several blocks should reduce floating point associated errors which can reach significant values with careless coding.
```
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Also all modes can be unified and can reuse the same acquisition code, nice... :)
```
```
```I hope to have an updated version of that article available soon.
```
```

```
```From the 2.5 ns single shot resolution, I deduce a 400 MHz count clock.
```
```
Yes. It is approx. 400MHz.
```
```
OK, good to have that verified. Free-running or locked to a 10 MHz
reference?
```
```
Locked to OCXO (10MHz).

All the best!
```
Oleg
```_______________________________________________
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