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HP 5335A Timer / Counter - Anything i should know?

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Dr. Frank:
Ok, I fired up my 5335A @ 9:39h. Room temperature was about 21.1°C, Gate Time 12.5sec for 1x10-10 resolution.
Reference is the Trimble Thunderbolt, with the "good" Trimble OCXO inside. Samples vary 1 digit only, i.e. by +/- 1x10-10.

  9:39 => 9.999 999 970 MHz
10:34 => 9.999 999 969 MHz
11:24 => 9.999 999 967 MHz

So the warm-up or retrace effect (oscillator was off before) is <= 3x10-10
I opened the lid, and attached a thermocouple thermometer on top of the case of the 10811.

12:00 => 9.999 999 970 MHz @ 31.6°C, just opened lid
12:45 => 9.999 999 970 MHz @ 38.0°C, open
13:00 => just closed lid, 32.0°C
13:17 => 9.999 999 969 MHz @ 29.4°C, closed
14:17 => 9.999 999 969 MHz @ 29.3°C, closed

So, the change over temperature is about/less than 1x10-10 over a 9°C change.

Your OCXO seems to be too sensitive against temperature changes, although it might still be in spec. of the 5335A manual, page 1-4, i.e. <7x10-9, 0 to 50°C.

My 5335A drifted by about -2.2x10-9 over at least 2 years, maybe longer, see Reply #27 here in this thread. OCXO was continuously running since that time.

Frank


tkamiya:
I guess you have a particularly good OCXO.  I know mine sat idle for years before I started playing with it.  I'm going to keep it plugged in for a while and repeat the test. 

Maybe all it needs is a cup of morning coffee.

In few days, I will have another 5335A, this time with factory option 10.  So I will be able to perform a direct comparison.

I actually have many rubidium modules.  The problem is power consumption.  It takes 2.5A total per spec, 1.8A actual measurement.  I actually tried to fit that all in.  I couldn't find a good placement for the power supply to be not near input and not near Rb.  So I am going with an external solution.

Dr. Frank:
Maybe, but in my memory, the other (repaired) 10811 inside the 5370B performs similar.

I also switch off my FRS-C Rb standard, due to high power consumption.. as it's mandatory to mount them on a big heat sink / metal plate.
Several Rbs inside one case, with one common heat sink might be a problem.

I packed 2 power supplies, 1 Rb, and the GPSDO inside a slim 19" case.. everything fine so far, only the Rb affects the Trimble stability a little bit.

Frank

tkamiya:
I might have exponent expression wrong.  My measurement was : 10,000,000,00x where x changes.  That's 10^-9? or 10^-10?  Input is 10MHz.  I always mess this up!

The GPS I have is PRS-10 and FRS-C.  I intend to use former and slave it to GPS.  To avoid any interactions, power supply will be linear and external.  So it'll be shielded from temp change and magnetic field.   

I am revamping my house standard.

I was also surprised how much Rb drifts.  It took good 24 hours to completely stabilize.

Dr. Frank:

--- Quote from: tkamiya on February 21, 2019, 03:30:24 pm ---I might have exponent expression wrong.  My measurement was : 10,000,000,00x where x changes.  That's 10^-9? or 10^-10?  Input is 10MHz.  I always mess this up!

The GPS I have is PRS-10 and FRS-C.  I intend to use former and slave it to GPS.  To avoid any interactions, power supply will be linear and external.  So it'll be shielded from temp change and magnetic field.   

I am revamping my house standard.

I was also surprised how much Rb drifts.  It took good 24 hours to completely stabilize.

--- End quote ---

That change would be x * 10-10.
The un-modified 5335A has 4s max. Gate Time, so only 10-9 will be displayed/resolved.
So maybe you should have a 2nd look, what you really measured.

My FRS-C needs about one week, until it has stabilized to parts in 10-11.. that drift-time always depends on the limit criterion used.
I have provided an external potentiometer to adjust the Rb to 2*10-12, but drifts are on the order of 1*10-11.

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