[time-nuts] Symmetricom 1111C OCXO question
Hello all, I've a C OCXO (inside a Symmetricom 5045A that is inside an Oscilloquartz OSA 5585) that refuses to start. It seems that one voltage regulator is not operating, with only 2V at its output while it should have (I think...) around 12V. I've partially analyzed the circuit, and it is nothing from other world: a 6.9V reference diode, driving an operational amplifier, driving a NPN transistor. But the 6.9V reference diode is biased from the regulator output, so... if the regulator does not provide output, the zener is not biased, and then... the regulator does not provide output. So it must be some kind of start-up circuit, that makes the transistor to conduct a bit, or to bias the diode, when power is applied. I've been looking around, but not found it yet. I have make a quick test by placing a 6k8 resistor between the collector and the base of the transistor to make it conduct, and then the regulator starts, provides adequate output (12.5V), and also the 5MHz output appears. Any idea is welcome :) Best regards, Javier ___ 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.
Re: [time-nuts] Symmetricom 1111C OCXO question
Hi Normally that sort of circuit has a “boot strap” pull-up resistor that weakly biases the diode to get things running at start up. Bob On Apr 3, 2014, at 11:08 AM, Javier Herrero jherr...@hvsistemas.es wrote: Hello all, I've a C OCXO (inside a Symmetricom 5045A that is inside an Oscilloquartz OSA 5585) that refuses to start. It seems that one voltage regulator is not operating, with only 2V at its output while it should have (I think...) around 12V. I've partially analyzed the circuit, and it is nothing from other world: a 6.9V reference diode, driving an operational amplifier, driving a NPN transistor. But the 6.9V reference diode is biased from the regulator output, so... if the regulator does not provide output, the zener is not biased, and then... the regulator does not provide output. So it must be some kind of start-up circuit, that makes the transistor to conduct a bit, or to bias the diode, when power is applied. I've been looking around, but not found it yet. I have make a quick test by placing a 6k8 resistor between the collector and the base of the transistor to make it conduct, and then the regulator starts, provides adequate output (12.5V), and also the 5MHz output appears. Any idea is welcome :) Best regards, Javier ___ 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.
[time-nuts] NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock
Full story at http://www.nist.gov/pml/div688/nist-f2-atomic-clock-040314.cfm Edésio ___ 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.
Re: [time-nuts] Symmetricom 1111C OCXO question
Hello! Yes, I was thinking something like that, but was not able to find it. After analyzing somewhat more, I'm finding that the problem seems more subtle. Since the gain of the operational is 1, and there is a positive feedback (the diode bias from the output), the output voltage should build up until reaching the zener threshold and then stabilize. But it only reach 2V, and remains there. The zener is biased using a 2k resistor. A further examination reveals that the zener also supplies a reference voltage to three sections of a quad X9241 digital potentiometer, through resistors (1k for each of two sections, 10k for the other). The X9241 receives a 5V supply from a MIC5205-5 regulator, that takes its input also from the output of the main regulator. The X9241 is non-volatile, and has the I2C bus accesible from outside the oscillator. When the output voltage is locked at ~2V, the output of the MIC5205 is also ~2V and in this condition is seems that the resistance to ground of the X9241 sections (nominally 10k each) is a lot lower, so they load too much the reference diode, and makes the voltage at the zener not to go up more. So I suspect that the output of the MIC5205 is activated too early, and when ramping up, it creates the lock-up. I've tested to put a 1000uF capacitor at its output to try to delay its turn-on, and then the circuit starts up OK - the voltage at the reference diode is the expected, the output of the regulator is ok, the output of the oscillator is ok. The MIC5205 has an enable pin, but it is tied to the input, and also has a bypass pin in order to connect a bypass capacitor to enhance its noise performance and power supply noise rejection, and this capacitor also has an effect on the regulator turn-on time. There is in fact a ceramic capacitor connected there. So tomorrow I will test to add some capacitance in parallel with it and see what happens. Normally I would doubt that the ceramic capacitor is bad, but I would also be surprised that the design of the circuit is so marginal that a slightly faster turn-on time in a secondary regulator is able to create this havoc :) Best regards, Javier On 03.04.2014 23:41, Bob Camp wrote: Hi Normally that sort of circuit has a “boot strap” pull-up resistor that weakly biases the diode to get things running at start up. Bob On Apr 3, 2014, at 11:08 AM, Javier Herrero jherr...@hvsistemas.es wrote: Hello all, I've a C OCXO (inside a Symmetricom 5045A that is inside an Oscilloquartz OSA 5585) that refuses to start. It seems that one voltage regulator is not operating, with only 2V at its output while it should have (I think...) around 12V. I've partially analyzed the circuit, and it is nothing from other world: a 6.9V reference diode, driving an operational amplifier, driving a NPN transistor. But the 6.9V reference diode is biased from the regulator output, so... if the regulator does not provide output, the zener is not biased, and then... the regulator does not provide output. So it must be some kind of start-up circuit, that makes the transistor to conduct a bit, or to bias the diode, when power is applied. I've been looking around, but not found it yet. I have make a quick test by placing a 6k8 resistor between the collector and the base of the transistor to make it conduct, and then the regulator starts, provides adequate output (12.5V), and also the 5MHz output appears. Any idea is welcome :) Best regards, Javier ___ 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. ___ 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.
Re: [time-nuts] Symmetricom 1111C OCXO question
Other idea than leaving the 6K8 resistor? On Thu, Apr 3, 2014 at 5:08 PM, Javier Herrero jherr...@hvsistemas.eswrote: Hello all, I've a C OCXO (inside a Symmetricom 5045A that is inside an Oscilloquartz OSA 5585) that refuses to start. It seems that one voltage regulator is not operating, with only 2V at its output while it should have (I think...) around 12V. I've partially analyzed the circuit, and it is nothing from other world: a 6.9V reference diode, driving an operational amplifier, driving a NPN transistor. But the 6.9V reference diode is biased from the regulator output, so... if the regulator does not provide output, the zener is not biased, and then... the regulator does not provide output. So it must be some kind of start-up circuit, that makes the transistor to conduct a bit, or to bias the diode, when power is applied. I've been looking around, but not found it yet. I have make a quick test by placing a 6k8 resistor between the collector and the base of the transistor to make it conduct, and then the regulator starts, provides adequate output (12.5V), and also the 5MHz output appears. Any idea is welcome :) Best regards, Javier ___ 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.
Re: [time-nuts] Symmetricom 1111C OCXO question
On 03.04.2014 18:25, Azelio Boriani wrote: Other idea than leaving the 6K8 resistor? Yes... I would prefer to know why the little thing has stopped working. The 6k8 resistor has also probed to be a marginal solution. The operational amplifier is a Burr-Brown one (don't have the p/n at hand now), and since it was my first suspect, I replaced it with a similar (but not the same) part from Linear Technology that I had at hand. With this one, I tested the resistor trick. After concluding that the original opamp was ok, I have put it back. With the original one, the resistor trick did no longer work, so it was not only a dirty solution, but also very marginal. So... I would prefer to find and solve the real failure :) Regards, Javier ___ 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.
Re: [time-nuts] NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock
Wow, if 1 second in 300 million years is correct, that's around 1 E-16th. M On Thu, Apr 3, 2014 at 2:51 PM, Edesio Costa e Silva time-n...@tardis.net.br wrote: Full story at http://www.nist.gov/pml/div688/nist-f2-atomic-clock-040314.cfm Edésio ___ 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.
[time-nuts] maybe OT: GLONASS
I do not have a GLONASS receiver running at home at this time, but the media reported a total GLONASS outage a day or so ago. Was it real or just rumor? A co-worker in the lab at my day-job says he thinks he caught a GLONASS RX acting badly. Just technical curiosity. Sorry for BW. -Brian, WA1ZMS/4 ___ 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.
Re: [time-nuts] NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock
It's true that this is really a feat given the difficulty of measuring these systematics. Not to toot my own horn but... http://www.nist.gov/pml/div689/20140122_strontium.cfm . even just a few months ago we were talking about mid E-18 using an optical clock. -Ben On Thu, Apr 3, 2014 at 6:24 PM, Michael Perrett mkperr...@gmail.com wrote: Wow, if 1 second in 300 million years is correct, that's around 1 E-16th. M On Thu, Apr 3, 2014 at 2:51 PM, Edesio Costa e Silva time-n...@tardis.net.br wrote: Full story at http://www.nist.gov/pml/div688/nist-f2-atomic-clock-040314.cfm Edésio ___ 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. ___ 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.
Re: [time-nuts] maybe OT: GLONASS
They apparently uploaded bad ephemeris data to the system and confused the receivers. It took them about 12 hours to straighten it out. ---Kenton A. hooverken...@nemersonhoover.org+1 415 830 5843 I do not have a GLONASS receiver running at home at this time, but the media reported a total GLONASS outage a day or so ago. Was it real or just rumor? A co-worker in the lab at my day-job says he thinks he caught a GLONASS RX acting badly. Just technical curiosity. Sorry for BW. -Brian, WA1ZMS/4 ___ 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.
Re: [time-nuts] maybe OT: GLONASS
Some details: http://gpsworld.com/glonass-gone-then-back/ Outage map (adjusted color version attached): http://gpsworld.com/wp-content/uploads/2014/04/glonass_problem-300x210.jpg /tvbattachment: 2014-glonass-outage.gif___ 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] Water on Enceladus - What does this imply about NASA'a ability to measure frequency?
I just read about a discovery of a liquid water ocean on Saturn's moon Enceladus. The method used was to measure the velocity of a spacecraft as it makes a close fly-by. Gravitational anomalies will cause the spacecraft to speed up or slow down as it flies over massive objects like mountains. With three pass they now have a 3 dimensional map of density distribution. It must be very sensitive if they can tell liquid water from ice by its gravitational field. (or even rock from ice) They say they can measure the spacecraft's velocity to 90 microns per second. They do this by measuring the Doppler sift of the transmitter.I've been trying to figure out what 90 microns/sec means in terms of frequency. But I think(?) I need to know the orbital velocity of Enceladus. -- Chris Albertson Redondo Beach, California ___ 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.
