[time-nuts] FE-5680A tuning vs resonant peaks

[Jeff Woolsey]

I have tweaked mine to my satisfaction now.  An offset of -768 gets it
as close as I can measure under sub-optimal conditions. See results at
bottom.

I am still curious as to whether Rubidium exhibits the same resonance
peaks that Cesium does, per Tom Van Baak's graph at
http://leapsecond.com/images/cfield.gif .


> Hi
>
> A few generic Rb information points:
>
> 1) All the telecom Rb’s need an external heatsink. To just mount them on
> a PC board, you need a lot of airflow (like fans …). 
>
> 2) Heat sinking improves the lifespan of these devices. Without a heatsink,
> a year or two is doing pretty well. With a heatsink that gets the base to 40C
> (possibly heatsink + small fan) a decade or more is possible. 

It sits on a square-foot slab of steel to the corner of which is mounted
a Panavise base.


>
> 3) If your Rb has a PPS output, cal is pretty easy. Just compare the pps
> to a < $20 GPS module with a scope. A day or three of tweaking should 
> get you pretty close. 

It does, but the generic problem with this technique is that there is an
arbitrary constant offset between the two pulses.  The first time I did
this some years ago, I set an 8-digit counter to show the time
difference between the two pulses (~735ms that time), then took a
timestamped photo every ten minutes or so, did some math, and found the
Rb and the GPSDO were within 2e-10 of each other. You want the delta as
stable as possible.

There's also the Lissajous method.

I never run mine for more than a week, and often less than a day.  It's
more of a Because I Can sort of thing...


>
> 4) With very few exceptions telecom Rb’s either have rotten phase noise / spurs
> or they have horrible phase noise / spurs. If you are going to do anything 
> “fancy” (like microwaves) with one, you will need a cleanup loop. 

Fortunately for me, I am not....


>
> 5) Many outfits produced a wide range of parts, all with the same part number.
> What you have with a XXXX model number on it may be *very* different than 
> what I have with the same … errr ... FE-5680 model number on it. 

Basically, the two [non-]programmable units mentioned earlier.  I have
the non- version.  It has only the DE9 connector.


>
> 6) Most Rb’s have some sort of crystal oscillator in them. There often is an
> adjustment (re-centering) needed on surplus parts. 

On tindie, there's also Nick Sayer's GPS disciplining board for the
FE-5680A.


>
> 7) Like OCXO’s Rb’s do have a warmup / retrace process that runs into 
> days. They also are sensitive to temperature, voltage, pressure, and 
> humidity. Compared to an OCXO, most of these sensitivities are pretty
> small. 
>
> As mentioned in a number of posts, in a lot of ways, an Rb makes a pretty
> good basement lab standard. Compared to a GPSDO, there are a lot
> fewer things to go wrong.
>
Other than the lamp life...  I've heard of ways to rejuvenate it.  Mine
spends 99.44% of its time powered off, though.

==

Here's the output from a Python script I wrote to evaulate oscillator
performance (I'm too impatient to wait for ADEVs) using vxi11 to talk to
a LAN-connected GPIB controller.  And while this counter does do
statistics, it doesn't do linear regression.  This is from this morning;
it was behaving almost as well last night.


bash-4.3$ python count-one-adhoc.py 1e7
Given ideal  1e7
HEWLETT-PACKARD,53131A,0,3944
Reference is EXTERNAL at +1.00000E+007 Hz
3.452 Previous gate time
Suggested gate time 1.79330192372
1.793 Gate time
1589572346.83 first time
0 bias
10000000.0 expected value

12 readings to take
 1 9999999.9998 Hz 1.93545103073 s 1.93545103073 delta s
 2 10000000.0 Hz 3.87260103226 s 1.93715000153 delta s
 3 9999999.9998 Hz 5.80996990204 s 1.93736886978 delta s
 4 10000000.0002 Hz 7.74672698975 s 1.93675708771 delta s
 5 10000000.0002 Hz 9.68287706375 s 1.93615007401 delta s
 6 9999999.9999 Hz 11.6207020283 s 1.93782496452 delta s
 7 10000000.0004 Hz 13.5647189617 s 1.94401693344 delta s
 8 10000000.0 Hz 15.5021290779 s 1.9374101162 delta s
 9 10000000.0003 Hz 17.4395709038 s 1.93744182587 delta s
10 10000000.0002 Hz 19.3772699833 s 1.93769907951 delta s
11 10000000.0 Hz 21.3132119179 s 1.93594193459 delta s
12 9999999.9997 Hz 23.2543890476 s 1.94117712975 delta s

151.119617939 Sum s
2440.26380663 Sum s^2
120000000.0 Sum y
1.20000000001e+15 Sum y^2
23.2543890476 Sum ds
45.0639478477 Sum ds^2
1511196179.4 Sum ys

10000000.0 Hz  mean
0.150755672289 Hz  std dev

12 readings in 23.2543890476 seconds, should be 21.516
1.93786575397 delta t mean, 0.144865753969 dead time, 0.144865753969 also,  8.07951778966 %
0.00240610675374 delta s std dev

1.50755672288e-08 stability? 15.0755672 ppb
4.16655598912e-12 accuracy?  4.1665560 ppt

second denominator  2.0
0.000215087265483 correlation
3.78864265201e-06 slope
9999999.99999 intercept
10000000.0 Hz  hat in the middle
10000000.0001 Hz  hat # 17 at about 32.9437178175 s
bash-4.3$ 

-- 
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel.  -Crow on solitaire