Bill,
A technique similar to this is used in the HP5328A counter, when
equipped with the option 040, and when doing the TI averaging.
Noise is intentionally added into the 100 MHz control loop, and then
multiple measurements is averaged. This way, the sample point moves
around it's average, and you can get better average resolution this way.
However, the single-shot resolution is still just 10 ns.
Since then interpolation of single-shot events have been investigated,
and is now down to 200 fs in the best counter I know of (and have).
Cheers,
Magnus
On 02/06/2015 07:52 AM, Bill Hawkins wrote:
Referring to a 1952 manual on servo systems, jitter seems to be noise
in the system, while dither is intentionally introduced to get a servo
through its dead space (usually caused by static friction).
The dead space in a counter is the interval between least significant
integers.
Thus the amplitude of the dither is the size of that dead space at a
frequency
that will be lost in the average.
I can see how this would work for a servo system, but how can a counter
display
more resolution than its least significant digit?
Bill Hawkins
-----Original Message-----
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus
Danielson
Sent: Wednesday, February 04, 2015 5:41 PM
To: time-nuts@febo.com
Cc: mag...@rubidium.se
Subject: Re: [time-nuts] T.I. questions
Joe,
The single-shot resolution of the Option 040 series input is 10 ns.
The T.I. interval option adds jitter to make the averaging useful.
If your PPS was instead a burst or a clock, comparing it to your clock
would make more sense and you could use that higher resolution.
If I had a GPIB interface for my 5328A, I would play around with it
more.
I think I recall a 10 ps resolution being achievable according to fancy
specs, with averaging to it's max.
Cheers,
Magnus
On 02/04/2015 09:58 PM, Joseph Gray wrote:
Sorry for the simple questions. Old hands can simply ignore this
message if it bothers you.
I have an HP 5328A that I have pieced together from broken units. As
soon as I make a ribbon cable for the GPIB card, I want to use it for
T.I. measurements. I know it isn't nearly as good as a 5370, but it is
what I have at the moment.
The manual states that the Universal module adds dithering to the
multiplied 100 MHz internal reference. If I use a GPSDO as an external
reference, will this multiplying/dithering allow me to use the same
GPSDO (divided down to PPS) on either the START or STOP inputs? If
not, then how about using a different GPSDO as the external reference?
Or even an FE5680A rubidium?
If I read the specs correctly, using T.I. averaging on the 5328A, a
1000 s average should get me 100 ps resolution? With this particular
instrument, what is the best, useful resolution I can expect?
Joe Gray
W5JG
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