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 <[EMAIL PROTECTED]> 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@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: [EMAIL PROTECTED] > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts