[time-nuts] Measuring ADEV for a beginner

[Magnus Danielson]

That will work as a starting-point.

When you look at your ADEV plot, you will notice a 1/tau curve for the 
lower taus, that is due to your counters limitations. If you need to go 
below that, you need a better counter, but for the moment you should 
start believe the plot as it flattens out, that has more to do with your 
signal, unless that is the same as your reference or a very high 
measurement floor of the counter.

A good test is to split your reference into the start and stop inputs, 
and then measure the amount of noise you have. Preferably with a 
slightly longer cable to the stop channel. This will give you the noise 
floor of the counter, for that signaltype and trigger-point.

There are ways to improve things if your noise is higher than the 
single-shot resolution, as you read out the ADEV at tau=1s.

Cheers,
Magnus

On 11/01/2014 09:43 PM, Anthony Roby wrote:
> Thanks - seems that I should be able to do this with my Racal-Dana 1992 counter.
>
> Anthony
>
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: Saturday, November 01, 2014 1:29 PM
> To: time-nuts at febo.com
> Cc: magnus at rubidium.se
> Subject: Re: [time-nuts] Measuring ADEV for a beginner
>
> Anthony,
>
> On 11/01/2014 02:29 PM, Anthony Roby wrote:
>> I've been reading a lot about ADEV and following the threads on the list, particularly Karen's in-flight thread.
>> What I haven't come across is a simple explanation of the basic setup required to go about collecting the data.
>> John Miles referenced this page http://www.ke5fx.com/tpll.htm, and the
>> simple setup at the bottom of the page looks like a reasonable place
>> to start.  Seems that I'd need to acquire a phase detector and build
>> or buy some filters and the amp.  I can probably figure that out, but how do I get the data into a PC?  Is there a basic hardware and software setup that someone could point me to or recommend?
>
> The time-interval counter, such as HP5370 or SR620, get started (channel
> 1) by a reference clock, such as 1 PPS and is then stopped (channel 2) by signal under test. The counter is typically read out through GPIB, even if some counters have serial interface and maybe even USB or Ethernet for really new (or retro-fitted), and the recommended path is to get a GPIB to USB interface for instance.
> Then use John Miles TimeLab.
>
> Cheers,
> Magnus
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