Ed I did not see any current, but that is also due to the fact that there is most likely at least 10 K between pin 2 and the varactor. Most likely if it was biased for instance + 12 Volt, there would also be a resistor before the diode. I suspect John is right that with my + voltage the diode was forward biased and blocked oscillation. Maybe this one was strictly - tuning voltage, hope so. I will run it for a time and observe stability. May be similar to HP 10811 bias. Thanks Bert In a message dated 8/10/2012 11:28:46 A.M. Eastern Daylight Time, ed_pal...@sasktel.net writes:
Hi Bert, I see on the data sheet that the tuning voltage is supposed to be -10 to +10 volts and that the supply voltage is +22 to +30 volts. I suspect that one side of the varactor is supposed to be biased at one half of the supply voltage. But in your case, it looks like that bias is now at zero volts due to an internal short - either a short between traces or, more likely, a capacitor failure. When you apply a positive voltage, you're changing the DC voltages in the oscillator circuit which disrupts the oscillator. When you apply a positive voltage to the EFC lead, is there a current flow into the lead? Since a varactor is always supposed to be reverse-biased there shouldn't be any current. Ed On 8/10/2012 4:46 AM, ewkeh...@aol.com wrote: > Bjoern > Thank you for the link I am able to change the frequency 4 Hz from - 2Hz ( > 0V) to + 2 Hz (-12.2V) using pin 2. Reading the info that you got me > probably explains the slot next to the connector, but I experience a much wider > tuning range on pin 2 and John is right any positive voltage forward biases > the diode cutting off oscillation. Will do some testing. > Thanks again Bert > > > In a message dated 8/10/2012 6:28:17 A.M. Eastern Daylight Time, > b...@lysator.liu.se writes: > > Bert, > > Good that you got the EFC working! But I would be a bit suspicious of > needing -13V. > > It seems from: > http://www.ece.gatech.edu/academic/courses/ece4007/08fall/ece4007l01/al4/dat > asheets/symmetricon_oscillator_instructionsheet.pdf > > that the default EFC configuration is (0 to +10)V with a range of 4e-7 > (2Hz). From the same document there are a lot of other EFC configurations, > but none that goes outside of +-10V. > > My 1200 has about 3.5Hz tuning range on (0,10)V. Se attached jpg. I did > not check behavior on negative EFC voltage. > > -- > > Björn > >> John, >> that did the trick I can tune it with a negative voltage, minus 13 gives me plus 2 Hz but this unit came out of a FTS 5000 and it had a positive >> tuning voltage. >> Bert >> >> >> In a message dated 8/9/2012 9:13:29 P.M. Eastern Daylight Time, >> jmi...@pop.net writes: >> >>> John >>> Oven did reduce in current and I can not imagine that it would be that >>> close with an overheated oven. At 0 V it is within .5 Hz of what they normally are. Ground has no effect but even 0.8 V on pin 2 stops oscillation >> That's a suspicious-sounding voltage. Are you sure you're not >> forward-biasing the varicap? Maybe some of these OCXOs were specified >> for use with negative EFC voltage. >> >> If so, then driving the diode with a negative voltage should raise the >> operating frequency (which is what you want.) >> >> -- john, KE5FX >> www.miles.io >> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.