[time-nuts] Bad batch of HP10811's

Didier Juges didier at cox.net
Fri Jan 19 23:53:28 EST 2007


Warmup data on the HP 10811:

Here is some data collected on the internal HP 10811 timebase in my HP 
5370A counter, which had been turned off and plugged off for about 3 days.

21:39:25,  9999798.6
21:39:35,  9999806.0
21:39:46,  9999822.6
21:39:55,  9999836.8
21:40:06,  9999853.2
21:40:15,  9999866.8
21:40:26,  9999881.7
21:40:35,  9999892.4
21:40:46,  9999904.1
21:40:56,  9999913.1
21:40:58,  9999915.2
21:41:07,  9999923.0
21:41:16,  9999930.1
21:41:25,  9999936.5
21:41:36,  9999944.0
21:41:46,  9999949.3
21:41:55,  9999954.3
21:42:06,  9999959.9
21:42:15,  9999964.0
21:42:26,  9999968.6
21:42:35,  9999971.8
21:42:45,  9999975.2
21:42:54,  9999977.9
21:43:05,  9999981.0
21:43:17,  9999983.9
21:43:26,  9999985.9
21:43:35,  9999987.8
21:43:46,  9999990.0
21:43:55,  9999991.3
21:44:07,  9999992.9
21:44:16,  9999994.0
21:44:25,  9999994.9
21:44:36,  9999996.1
21:44:45,  9999996.9
21:44:56,  9999997.7
21:45:06,  9999998.3
21:45:15,  9999998.9
21:45:17,  9999999.0
21:45:19,  9999999.1
21:45:21,  9999999.2
21:45:24,  9999999.3
21:45:26,  9999999.4
21:45:36,  9999999.7
21:45:45,  9999999.8
21:45:56,  9999999.9
21:46:05,  9999999.9
21:46:08,  9999999.9
21:46:10,  10000000.0

After that, the display was a stable 10,000,000.0 for the next 15 
minutes (one reading was 10,000,000.1), then I stopped the data collection.

The counter used was the HP 5334B with the Thunderbolt as external 
reference.

Ambient temperature: about 22 degrees C (cool)

Bottom line: about 200 Hz from a cold start and about 7 minutes to 
within 0.1 Hz of final frequency.

Didier KO4BB


Didier Juges wrote:
> That is interesting. I have not checked the 10811 for that particular behavior, but I have checked a number of cheap, non TC crystal oscillators, and the initial drift has always been much smaller, in the order of 100's of Hz, not 1,000's, scaled for 10 MHz.
>
> I refer to the crystal oscillators inside my various ham radio gear and non-TCXO controlled instruments, such as the 5334B counter I have.
>
> It may be due to the fact that the crystal in the HP 10811 is optimized for flat temperature sensitivity around the operating point of the oven, when the cheap crystals I have checked are optimized around ambient (if they are optimized at all).
>
> I have several 10811's here (one by itself, the others inside instruments) and now that you picked my attention, I have to do the test :-)
>
> It's easy to plot it against the Thunderbolt with a counter hooked to the GPIB controller and with my logging software running. I shall report here soon :-)
>
> Didier KO4BB
>
>
> ---- Jeroen Bastemeijer <J.Bastemeijer at TUDelft.nl> wrote: 
>   
>> Dear Time-nuts,
>>
>> Just a quick experiment. I started with the cold 10811 OCXO (switched 
>> off for >24 hours). I connected it to a counter and noted the frequency 
>> every 30 seconds. (last two measurement each 5 minutes).
>>
>> You can see the curve in the attached PDF. The offset at t=0 was 1706 Hz 
>> (Compared to 10.000000MHz).
>>
>> After 10 minutes warm-up the total offset is 0.75Hz (compared to 
>> 10.000000MHz) and offset is 0.12Hz from the "final" value. According to 
>> the spec the offset should be within 5*10^-9.
>>
>>  From this I conclude the oscillator is not faulty. Sorry, Didier  ;-)
>>
>> The possible reason for this offset is probably not the crystal, but the 
>> tempco of the rest of the circuit. The oven heats up till about 82 
>> degrees centigrade. A PN-juntcion at room temperature (22 degrees) will 
>> increase 60 degrees in temperrature, it's forward voltage will change by 
>> approx. 120 mV!!!!! This change will lead to a significant change in 
>> circuit properties (e.g. of the oscillator and the attached AGC circuit).
>>
>> Probably this was the reason HP specfied it's oscillator first after 10 
>> mins of warm-up.
>>
>> This makes me wonder: If an oscillator gives a big offset, the 
>> ovencontroller may be faulty... not working at all, or not getting warm 
>> enough.
>>
>> Jeroen PE1RGE
>>
>>
>>
>> The raw data:
>> Time Frequncy [MHz]  Offset [Hz]
>> 0    9,998294    1706
>> 30    9,998405    1595
>> 60    9,998645    1355
>> 90    9,998854    1146
>> 120    9,999038    962
>> 150    9,999197    803
>> 180    9,999349    651
>> 210    9,999466    534
>> 240    9,999569    431
>> 270    9,999666    334
>> 300    9,99974    260
>> 330    9,999804    196
>> 360    9,999858    142
>> 390    9,999906    94
>> 420    9,99994027    59,73
>> 450    9,99996696    33,04
>> 480    9,99998633    13,67
>> 510    9,99999979    0,21
>> 540    10,00000062    -0,62
>> 570    9,99999958    0,419999999
>> 600    9,99999925    0,75
>> 900    9,99999933    0,67
>> 1200    9,99999937    0,630000001
>>
>>
>> Didier Juges wrote:
>>
>>     
>>> That sounds like an awful lot of drift, absolutely inconsistent with a 
>>> crystal oscillator of any kind.
>>>
>>> Either this OCXO is really sick, and just happen to end up at the right 
>>> frequency by accident, or it is an OCO (Oven Controlled Oscillator :-)
>>>
>>> Didier KO4BB
>>>
>>> Jeroen Bastemeijer wrote:
>>>  
>>>
>>>       
>>>> Dear Rick,
>>>>
>>>> Are you sure the 500Hz is too much for a cold oven? I checked my 5345A 
>>>> (recently acquired) counter, which was switched off for some time. 
>>>> Measuring the frequency directly after applying power and switching on, 
>>>> resulted in about 1640 Hz frequency offset. After warm up, the error is 
>>>> below 0.4 Hz. (The unit used here is a 10811a). The error drops pretty 
>>>> fast, allthough I didn't measure an accurate curve. Is the frequency 
>>>> difference caused by the tempco of the oscillator circuit?
>>>>
>>>> Cheers, 73s Jeroen PE1RGE
>>>>  
>>>>    
>>>>
>>>>         
>>> _______________________________________________
>>> time-nuts mailing list
>>> time-nuts at febo.com
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>>>
>>>
>>>
>>>  
>>>
>>>       
>> -- 
>> Ing. Jeroen Bastemeijer
>>
>> Delft University of Technology
>> Department of Electrical Engineering
>> Electronic Instrumentation Laboratory
>> Mekelweg 4, Room 13.090
>> 2628 CD Delft
>> The Netherlands
>>
>> Phone: +31.15.27.86542
>> Fax: +31.15.27.85755
>> E-mail: J.Bastemeijer at TUDelft.nl
>>
>>     
>
>
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