[time-nuts] any HP 5370B Available or other TIC

[Bob Camp]

Hi

The real answer (as always) is "that depends". Keeping things very simple
(ADEV only):

At one second Tau, a good eBay oscillator will be in the vicinity of
3x10^-12. The 5370 has a single shot resolution of 20 ps RMS. That might get
you to 2x10^-11. The 5370 won't let you do this level of 1 second ADEV
directly. 

The same oscillator *might* get to 1x10^-12 at 100 seconds. The 5370's 20 ps
would give you 2x10^-13 at 100 seconds. Between 1 and 100 seconds, the 5370
becomes useful for measuring ADEV in this case.

In both cases, you still need a reference that's as good as or better than
the oscillator you are testing. The numbers are all a comparison of
reference to device under test. This is true no matter what technique you
use. Since it's always a comparison, there are other approaches.

A quick and simple approach with what you have is a single mixer. Offset
(tune) the device you are testing by 1 to 10 Hz from your reference. The
Rakon would be at 10.000001 MHz and the Z3801 at 10.000000 MHz. Plug the
Rakon into one RF port on a double balanced mixer. Plug your reference into
the other RF port on the mixer. Take the beat note (1 to 10 Hz audio) out of
the IF port. Filter it a bit to get rid of the RF on it. Feed it into your
Keithly 776 counter. 

When the device you are testing moves by 0.1 Hz, the beat note does the
same. At 10 MHz 0.1 Hz is 1x10^-8. At 1 Hz 0.1 Hz is 10%. The mix down
"amplifies" the change in frequency by 1x10^7 in this case. If your Keithly
could read 9 good digits off of the 1 Hz, you would have 1x10^-18 data. 

Life is never this simple. Converting the audio sine wave to a square wave
is a noisy process. That limits the resolution you can actually get. Your
counter input is likely not ideal for this task. There are a variety of op
amp circuits you can use to significantly improve on it. You still won't get
1x10^-18, but you can get to 1x10^-12. With some care and luck you might
even do better than that. 

A chunk of perf board, and the parts you have sitting in a junk box will
probably do well enough to get you started. To buy simple stuff and wire it
up on perf board should be below $50. A full blown approach with a fancy
multi stage filter/limiter and a PC board might get you into the $200 range.


All this assumes that you offset the device you are testing from the
reference. That lets you use a single mixer. If you want a more general
approach where the device under test is not offset, then the DMTD is the way
to go. More money (more mixers), but it removes a constraint. 

Lots of ways to go.

Bob  

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Paul Cianciolo
Sent: Wednesday, August 17, 2011 11:11 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] any HP 5370B Available or other TIC

Hello Folks,
I am looking for an instrument that is better than Fluke 103a comparator.
The purpose of this piece of equipment is help me learn more about
oscillators and characterizing them
 
The HP5370B is the TIC I keep hearing about but I am not glued to that make
or model.
I wou;d like to hear suggestion from the group.
 
Another way to go might be to build one of those units where there is
a common oscillator is split and feeds the LO of 2 mixers.
The RF side comes from the DUT and the REF  
Sorry I cannot remember the acronym... MDMM????
 
I do have that Keithly model 776 Counter time with GPIB  I am really fuzzy
on this aspect...
 
Comments welcome 
 
Thank you
 
PaulC
W1VLF
 
  

From: To: Sent: 



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