Ed I think so too. I hope if it is a shorted capacitor it stays but looking at for instance at the bias of a 10811. There would be no capacitor right at the diode. I have the tuning network for a 1130 and it shows a 20 K to an internal +12 V Bert In a message dated 8/10/2012 2:01:22 P.M. Eastern Daylight Time, ed_pal...@sasktel.net writes:
Bert, I wasn't suggesting amps of current. A normal reverse-biased diode would give nanoamps of current flowing out. Microamps (or more) of current flowing in would show that the internal biasing of the varactor was messed up. A bad diode could also show current flowing in, but your success with negative voltage biasing suggests that the diode could be okay. Ed On 8/10/2012 11:31 AM, ewkeh...@aol.com wrote: > 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.