Re: [time-nuts] Trimble 34310-T EFC Question
FYI, if you are measuring the voltage with a fluke or similar meters, I've seen them throw a lot of noise onto a signal line. In many cases we've had to put an RC filter coming from the fluke to block the noise from the meter getting into the circuit! Also, you aren't running a KW Ham transmitter are you? Also, some CF bulbs are really noisy. I've also seen some PC's swamp out GPS receivers... Basically, I've learned the hard way to eliminate anything in the room first. Only then can you try to modify the circuit! Just some food for thought! Dan On 11/7/2013 10:41 AM, time-nuts-requ...@febo.com wrote: Message: 1 Date: Wed, 6 Nov 2013 19:40:31 -0800 From: John C. Westmoreland, P.E. j...@westmorelandengineering.com To: Bob Stewart b...@evoria.net,Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Trimble 34310-T EFC Question Message-ID: CAFtYB4wY0QEFwc4G2E=f5fknp85eofxijmamvx8ir-lw9yh...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Hello Bob, If you think you are getting any high frequency into the EFC control - it may be worth putting a(nother) low-pass filter in there. Are you measuring noise on that line? Do you have a snap-shot of a schematic? Or, can you take a picture of that circuit? I would hazard a guess you don't want to change the op-amp in such a way the gain is too high - the circuit could be designed for unity gain. A different choice in resistors could still yield unity gain and maybe knock down the noise a bit. I would need to put an ammeter in the circuit to determine if there was any meaningful current flow - without injecting noise of course... ;) 73's, John AJ6BC On Wed, Nov 6, 2013 at 7:26 PM, Bob Stewart b...@evoria.net wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Bob - AE6RV ___ 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] Trimble 34310-T EFC Question
Hi Dan, I'm measuring with an HP 3456A using 1 meter of unshielded twisted pair. I do not have an LC filter on the EFC line. The op-amp driver connects directly to the EFC port on the oscillator. I spoke to someone else who is using the same board and he reports the same problem when attempting to measure the EFC. His other equipment has been at least one generation newer than mine, so I assume the same for the voltmeter. I've been giving some thought to putting an LC on it. But since I can measure it without a problem at the input of the op-amp, that's gone to the bottom of my priorities list. Bob From: Dan Kemppainen d...@irtelemetrics.com To: time-nuts@febo.com Sent: Thursday, November 7, 2013 11:52 AM Subject: Re: [time-nuts] Trimble 34310-T EFC Question FYI, if you are measuring the voltage with a fluke or similar meters, I've seen them throw a lot of noise onto a signal line. In many cases we've had to put an RC filter coming from the fluke to block the noise from the meter getting into the circuit! Also, you aren't running a KW Ham transmitter are you? Also, some CF bulbs are really noisy. I've also seen some PC's swamp out GPS receivers... Basically, I've learned the hard way to eliminate anything in the room first. Only then can you try to modify the circuit! Just some food for thought! Dan On 11/7/2013 10:41 AM, time-nuts-requ...@febo.com wrote: Message: 1 Date: Wed, 6 Nov 2013 19:40:31 -0800 From: John C. Westmoreland, P.E. j...@westmorelandengineering.com To: Bob Stewart b...@evoria.net, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Trimble 34310-T EFC Question Message-ID: CAFtYB4wY0QEFwc4G2E=f5fknp85eofxijmamvx8ir-lw9yh...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Hello Bob, If you think you are getting any high frequency into the EFC control - it may be worth putting a(nother) low-pass filter in there. Are you measuring noise on that line? Do you have a snap-shot of a schematic? Or, can you take a picture of that circuit? I would hazard a guess you don't want to change the op-amp in such a way the gain is too high - the circuit could be designed for unity gain. A different choice in resistors could still yield unity gain and maybe knock down the noise a bit. I would need to put an ammeter in the circuit to determine if there was any meaningful current flow - without injecting noise of course... ;) 73's, John AJ6BC On Wed, Nov 6, 2013 at 7:26 PM, Bob Stewart b...@evoria.net wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Bob - AE6RV ___ 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] Trimble 34310-T EFC Question
Bob wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Generally, an EFC pin connects internally to one or more varicap diodes, which by definition must be reverse biased (thus, the only current flow is the reverse current (leakage) of the diode(s)). There is often an internal series resistor of 50-100k between the EFC pin and the diode(s). It is common to use an additional, external series resistor and shunt capacitor, generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, depending on the application. Of course, this additional pole needs to be taken into account in the loop stability analysis of the PLL. Best regards, Charles ___ 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] Trimble 34310-T EFC Question
Hi …….unless the oscillator has a bias / attenuator network internally to shift the region of the varicap’s capacitance/voltage curve the efc affects. That’s often done to modify the linearity of the tuning curve. It’s pretty simple to check. Put an ohm meter on it and see what it reads. Check on a couple of ranges in case you are forward biasing something. Bob On Nov 7, 2013, at 6:09 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Generally, an EFC pin connects internally to one or more varicap diodes, which by definition must be reverse biased (thus, the only current flow is the reverse current (leakage) of the diode(s)). There is often an internal series resistor of 50-100k between the EFC pin and the diode(s). It is common to use an additional, external series resistor and shunt capacitor, generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, depending on the application. Of course, this additional pole needs to be taken into account in the loop stability analysis of the PLL. Best regards, Charles ___ 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] Trimble 34310-T EFC Question
From: Charles Steinmetz csteinm...@yandex.com It is common to use an additional, external series resistor and shunt capacitor, generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, depending on the application. Of course, this additional pole needs to be taken into account in the loop stability analysis of the PLL. Thanks Charles, My exposure to this stuff is extremely limited, and this is a big help! I can plug this into LTSpiceIV and hopefully wind up with something that works at all ranges of this dithered PWM derived DAC. Bob From: Charles Steinmetz csteinm...@yandex.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, November 7, 2013 5:09 AM Subject: Re: [time-nuts] Trimble 34310-T EFC Question Bob wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Generally, an EFC pin connects internally to one or more varicap diodes, which by definition must be reverse biased (thus, the only current flow is the reverse current (leakage) of the diode(s)). There is often an internal series resistor of 50-100k between the EFC pin and the diode(s). It is common to use an additional, external series resistor and shunt capacitor, generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, depending on the application. Of course, this additional pole needs to be taken into account in the loop stability analysis of the PLL. Best regards, Charles ___ 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] Trimble 34310-T EFC Question
Thanks Bob, I have a spare oscillator, so it's a simple deal to put a meter on it, now that I know what to look for. Bob From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, November 7, 2013 6:27 AM Subject: Re: [time-nuts] Trimble 34310-T EFC Question Hi …….unless the oscillator has a bias / attenuator network internally to shift the region of the varicap’s capacitance/voltage curve the efc affects. That’s often done to modify the linearity of the tuning curve. It’s pretty simple to check. Put an ohm meter on it and see what it reads. Check on a couple of ranges in case you are forward biasing something. Bob On Nov 7, 2013, at 6:09 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Generally, an EFC pin connects internally to one or more varicap diodes, which by definition must be reverse biased (thus, the only current flow is the reverse current (leakage) of the diode(s)). There is often an internal series resistor of 50-100k between the EFC pin and the diode(s). It is common to use an additional, external series resistor and shunt capacitor, generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, depending on the application. Of course, this additional pole needs to be taken into account in the loop stability analysis of the PLL. Best regards, Charles ___ 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.
[time-nuts] Trimble 34310-T EFC Question
I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Bob - AE6RV ___ 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] Trimble 34310-T EFC Question
Hello Bob, If you think you are getting any high frequency into the EFC control - it may be worth putting a(nother) low-pass filter in there. Are you measuring noise on that line? Do you have a snap-shot of a schematic? Or, can you take a picture of that circuit? I would hazard a guess you don't want to change the op-amp in such a way the gain is too high - the circuit could be designed for unity gain. A different choice in resistors could still yield unity gain and maybe knock down the noise a bit. I would need to put an ammeter in the circuit to determine if there was any meaningful current flow - without injecting noise of course... ;) 73's, John AJ6BC On Wed, Nov 6, 2013 at 7:26 PM, Bob Stewart b...@evoria.net wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Bob - AE6RV ___ 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] Trimble 34310-T EFC Question
Bob, Most EFC circuits are relatively high impedance, i.e., around 50K. So, we are talking micro amps of current flow. If there is jitter it is most likely somewhere else in the circuitry OR you are seeing the natural noise in the GPS system. BillWB6BNQ Bob Stewart wrote: I think I may need to change the LPF feeding the EFC in my GPSDO to get rid of dithering jitter. Is there any point in adding a resistor and cap in the EFC line, or do I need to go back and change the values in the op-amp circuit feeding it? Currently an op-amp directly feeds the EFC pin. I guess this boils down to something like: is there any meaningful current flow in EFC circuit in this oscillator? Or should I add them but will I probably have to change the existing filter, as well? Bob - AE6RV ___ 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.
