[time-nuts] General questions about making measurements with time interval counter.
bob at evoria.net
Thu Jan 12 11:31:45 EST 2017
Normally I see somewhere between 2E-11 and 4E-11 at 1S tau on my 5370A, as in the blue trace on the attached plot. Am I misunderstanding your meaning? Granted, I am clocking the 5370A with a GPSDO, but I believe I see about the same thing with the HP10811. This test was 1PPS vs 1PPS on two different units.
The plot also has a test run by Tom, in orange, using his H Maser and a Timepod to show how poor the 5370 is compared to the Timepod below about 60S tau. These are essentially apples vs apples tests.
From: Bob Camp <kb8tq at n1k.org>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Thursday, January 12, 2017 8:27 AM
Subject: Re: [time-nuts] General questions about making measurements with time interval counter.
There are a number of ways to improve the resolution (and accuracy) of your data without spending
big piles of cash. They have been discussed here on the list many times over the last few years.
What I’m suggesting is that you dig into that ahead of taking data. You will dive into it eventually as you
look more and more at devices that are locked to some sort of stable reference internally.
Ideally you would like a device with a floor 5X to 10X better than what you are measuring. For ADEV style
data, the 5370 is a 1x10^-10 sort of device single shot (so 1x10^-9 is the limit at 10:1). With a lot of averaging
(which is not something you do with ADEV) you can get about 5X better than that as a floor. In either case, it is getting in the way of any
readings that are much below 1x10^-9 at one second. A low cost XO can hit that level of performance.
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