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]
10811coldstart.pdf
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