[time-nuts] Bad batch of HP10811's

[Didier Juges]

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
> >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >
> >
> >
> >  
> >
> 
> -- 
> 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
>