Re: [time-nuts] 5060A question
From: Bruce Griffiths [EMAIL PROTECTED] Subject: Re: [time-nuts] 5060A question Date: Tue, 08 Jan 2008 20:56:14 +1300 Message-ID: [EMAIL PROTECTED] Dave Carlson wrote: Hello, Since the source of the noise is the vibration of the Hot Wire Ionizer ribbon inside the CBT it will require using something other than pressure on the outer container to snuff it out. The outer steel of the CBT is rigid. Dave Which is why it transmits the sound so well. Its not the pressure but the acoustic damping. However material which has high acoustic damping also tends to be a good thermal insulator, so care must be taken to avoid overheating components. Agree. The idea isnt so much to stop the ribbon vibrating but attenuate the transmission of the vibration to the surrounding structures and ultimately the air. Indeed, this was my point. A correctly sized and located acoustic resonator with appropriate internal damping can help by absorbing the sound caused by the vibration. The fixed frequency suits our purpose here. In the land of EMC there are there ways to reduce interference: 1) Make the transmitter less efficient 2) Make the transmission path less efficient 3) Make the receiver less efficient For this case, 3 is clearly out of the question, but there are certainly alot of options in rule 2 (which can be seens as rule 1 depending on where you draw the boarder between transmitter and transmission path). Cheers, Magnus ___ 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] How to measure regulator noise?
I`d just hang an AC millivoltmeter[or microvoltmeter] across the regulator`s output. I use my H/P 400H, which will give readings down to about 50uV. If your regulator produces less noise than this [say a 723, with 2uV], then you`ll need a more sensitive meter. It might be wise to short the input wires of the meter, to check the inherent noise in the measurement setup - for meaningful results this should be, perhaps, no more than a tenth of the expected reading [depending on how riggerus you want to be]. Bear in mind that most analogue meters are average responding, and calibrated for a sinewave - so to get the RMS value for white noise [or whatever] a correction factor should be applied [depending also on what sort of accuracy you need/want]. If you want to *look* at the noise, I understand that one of the Tek 7000 series plug-ins is able to display very small amplitudes of this order. Again, because you may be dealing with comparitively small voltages [compared with those which might be induced due to hum fields etc], it would be wise to check the residual noise by shorting the probe[s] at the regulator. This is valid since the output impedance of the regulator is nearly zero. Go to it!,..Don C. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, January 08, 2008 10:03 AM Subject: Re: [time-nuts] How to measure regulator noise? Poul-Henning Kamp wrote: In message [EMAIL PROTECTED], Dave Brown writes: John You won't need much of a cap for DC blocking as inputs are hi-Ztoo big and the chargeup may well trigger the overrange condition. You need to put a shunt resistor after the capacitor if the input is hi-Z but an even better way is to offset the gnd clip with a couple of fresh batteries so that you can avoid the capacitor. Batteries have very low, but not zero noise, so what you do is: Put six fresh 1.5 volt batteries in series, so that three of them is the wrong way and the resultant voltage is zero and then you measure their noise. Then you put three of them the wrong way on your 5v supply, so that the output voltage is only .5V and then you measure the noise. That worked fine for me using a HP6885B This technique only offsets the voltage to within 3/4V of zero when measuring an arbitrary voltage regulator output. With a discrete regulator it is usually easy enough for test purposes to adjust the regulator output so that it is within a few tens of millivolts of the battery stack voltage. A low noise preamp with perhaps 40-60dB gain is still required before the spectrum analyser. Even residual dc voltages of a few tens of millivolts may saturate such an amplifier. A simple dc servo can be used to remove the residual offset (1V) without using electrolytic capacitors with their attendant leakage and noise. A low frequency cutoff well below 1Hz is possible without adding significant noise. Alternatively for measurements in the 10Hz to 100kHz range a preamp like that used in Linear Technology's AN83: http://www.linear.com/pc/downloadDocument.do?id=4172 may be useful. It uses electrolytic coupling capacitors together with low value resistors. For ultralow (milliHertz) frequency noise measurement AC coupling is best avoided altogether, if possible. Bruce ___ 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] 5060A acoustic noise issue
Brian, I once obtained a 5060A that was used in the time and frequency lab at HP. I guess it had sentimental value to them as they kept it going long after the 5061B had come out. It had a newer tube in it and more to the point it had one of the later 5061A/B style A11 oven controller modules installed. This provides DC to the hot wire and no acoustic noise! I can't remember where they shoe-horned it in as it is a taller module than the 5060As. These A11 units are obtainable and the modification would not be daunting. Best regards, Corby ___ 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] How to measure regulator noise?
On Jan 8, 2008, at 12:50, Don Collie wrote: I`d just hang an AC millivoltmeter[or microvoltmeter] across the regulator`s output. I use my H/P 400H, which will give readings down to about 50uV. If your regulator produces less noise than this [say a 723, with 2uV], then you`ll need a more sensitive meter. Electronic voltmeters or microvoltmeters have a noise bandwidth which is larger than the bandwidth on the front panel. The front panel bandwidth is related to accuracy and is not the -3dB bandwidth. The noise bandwidth is nearly always range setting dependent and can vary very much. I have seen a factor of four in noise bandwidth between adjacent range settings. The only way to have a good indication on noise is in a known and constant bandwidth. The noise bandwidth of a filter is not the same as the 3dB bandwidth and dependent of the filter order and shape. It is always more. Henk ___ 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] How to measure regulator noise?
Don Collie wrote: I`d just hang an AC millivoltmeter[or microvoltmeter] across the regulator`s output. I use my H/P 400H, which will give readings down to about 50uV. If your regulator produces less noise than this [say a 723, with 2uV], then you`ll need a more sensitive meter. It might be wise to short the input wires of the meter, to check the inherent noise in the measurement setup - for meaningful results this should be, perhaps, no more than a tenth of the expected reading [depending on how riggerus you want to be]. Bear in mind that most analogue meters are average responding, and calibrated for a sinewave - so to get the RMS value for white noise [or whatever] a correction factor should be applied [depending also on what sort of accuracy you need/want]. If you want to *look* at the noise, I understand that one of the Tek 7000 series plug-ins is able to display very small amplitudes of this order. Again, because you may be dealing with comparitively small voltages [compared with those which might be induced due to hum fields etc], it would be wise to check the residual noise by shorting the probe[s] at the regulator. This is valid since the output impedance of the regulator is nearly zero. Go to it!,..Don C. Don This method doesnt give the noise spectrum which can be important for use when powering VCXOs etc. The better discrete low noise regulators have very low noise so one still needs a low noise preamp. For noise measurements at frequencies below 10Hz a preamp with low noise and a low cutoff frequency can be challenging. Bruce ___ 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] 5060A acoustic noise issue
You might try Frequency Standards and Services in Colorado Springs for any parts. However installing the 5061A/B A11 Dc Oven Controller into a 5060A may not be simple. Dave - Original Message - From: corby d dawson [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Tuesday, January 08, 2008 8:48 AM Subject: [time-nuts] 5060A acoustic noise issue Brian, I once obtained a 5060A that was used in the time and frequency lab at HP. I guess it had sentimental value to them as they kept it going long after the 5061B had come out. It had a newer tube in it and more to the point it had one of the later 5061A/B style A11 oven controller modules installed. This provides DC to the hot wire and no acoustic noise! I can't remember where they shoe-horned it in as it is a taller module than the 5060As. These A11 units are obtainable and the modification would not be daunting. Best regards, Corby ___ 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] How to measure regulator noise?
Hi Bruce and Henk, Your point about Bandwidth is a valid one, and as you say, it depends on the application. The 400H has corner frequencies of about 10Hz, and 4Mhz, so the noise BW is a bit wider than this [Y/N?]. This setup can`t measure noise at very low Frequencies, or Frequencies much greater than the [nominal] 4Mhz, because the noise frequency components simply can`t get through. For my purposes the setup I described is adequate - I mainly want to compare one regulator with another [although it would be nice to be able to do so over the frequencies 0Hz to infinity]. I suggest that if a regulator proves itself quieter over a restricted BW such as I described, it is *probably* quieter at other frequencies too. Take that Bruce! ;-)..Don. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, January 09, 2008 9:26 AM Subject: Re: [time-nuts] How to measure regulator noise? Henk ten Pierick wrote: On Jan 8, 2008, at 12:50, Don Collie wrote: I`d just hang an AC millivoltmeter[or microvoltmeter] across the regulator`s output. I use my H/P 400H, which will give readings down to about 50uV. If your regulator produces less noise than this [say a 723, with 2uV], then you`ll need a more sensitive meter. Electronic voltmeters or microvoltmeters have a noise bandwidth which is larger than the bandwidth on the front panel. The front panel bandwidth is related to accuracy and is not the -3dB bandwidth. The noise bandwidth is nearly always range setting dependent and can vary very much. I have seen a factor of four in noise bandwidth between adjacent range settings. The only way to have a good indication on noise is in a known and constant bandwidth. The noise bandwidth of a filter is not the same as the 3dB bandwidth and dependent of the filter order and shape. It is always more. Henk Thus if one is to make useful comparative measurements with an AC voltmeter, an external filter which has a significantly narrower bandpass than that of the AC voltmeter is useful. A spectrum analyser with the capability of averaging cross power spectra has the added advantage (over an AC voltmeter) of being able to make meaningful measurements of noise below the noise of its input amplifiers (or the noise of external preamplifiers). Since its difficult to build a preamp with noise much below 10nV/rtHz whilst ensuring that the preamp input will survive worst case transients etc when connected to a power supply of 10V or more, such a capability is useful for measuring the noise of ultra low noise regulators which may have high frequency noise of 20nV/rtHz or less. For example the preamp used in Linear technologies AN83 is virtually guaranteed to be damaged by connecting its input to a powered up 20V supply. Off course, connecting it to the power supply before powering up the supply will (if the regulator output slew rate is sufficiently low) allow it to be used to measure the noise of higher voltage supplies (at least if higher voltage 330uF OSCON caps were available). However accidents/mistakes do happen (as do faulty regulators) and eventually the preamp input opamp will be destroyed. Using standard electrolytics for the input coupling capacitor for testing higher voltage supplies isnt particularly useful as they have increased leakage current and associated noise. Schemes such as using a relatively high resistance in series with the preamp input which is shorted out after the coupling capacitor has charged are not foolproof and eventually a mistake will lead to destruction of the preamp input stage. For circuit schematics of preamps with input protection schemes that allow power supplies with outputs greater than 5V to be tested see: http://www.ko4bb.com/~bruce/LNPS.html http://www.ko4bb.com/%7Ebruce/LNPS.html Bruce ___ 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] 5060A acoustic noise issue
Corby- That's interesting to know that somebody has performed the conversion at least once before. I have a 5060 donor chassis and maybe that would be the one to try and see how I might fit an A11 module in place of the A20. Thanks! -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of corby d dawson Sent: Tuesday, January 08, 2008 11:48 AM To: time-nuts@febo.com Subject: [time-nuts] 5060A acoustic noise issue Brian, I once obtained a 5060A that was used in the time and frequency lab at HP. I guess it had sentimental value to them as they kept it going long after the 5061B had come out. It had a newer tube in it and more to the point it had one of the later 5061A/B style A11 oven controller modules installed. This provides DC to the hot wire and no acoustic noise! I can't remember where they shoe-horned it in as it is a taller module than the 5060As. These A11 units are obtainable and the modification would not be daunting. Best regards, Corby ___ 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] How to measure regulator noise?
Don Collie wrote: Hi Bruce and Henk, Your point about Bandwidth is a valid one, and as you say, it depends on the application. The 400H has corner frequencies of about 10Hz, and 4Mhz, so the noise BW is a bit wider than this [Y/N?]. This setup can`t measure noise at very low Frequencies, or Frequencies much greater than the [nominal] 4Mhz, because the noise frequency components simply can`t get through. For my purposes the setup I described is adequate - I mainly want to compare one regulator with another [although it would be nice to be able to do so over the frequencies 0Hz to infinity]. I suggest that if a regulator proves itself quieter over a restricted BW such as I described, it is *probably* quieter at other frequencies too. Take that Bruce! ;-)..Don. Don If you have a PC sound card then it can be used with a suitable preamp to measure regulator noise spectral density over the [20Hz, 20kHz ] range. Except for switching regulators there's usually not much noise beyond 100kHz. Often linear regulator output noise may peak somewhere within this range. The location and the amplitude of the noise peak depends on the regulator output current and the characteristics of the regulator output capacitor. The originator of this thread needs to know the regulator noise spectrum detail in order to properly evaluate various regulators for use in low phase noise equipment. The high frequency noise of a regulator is not a reliable guide to its flicker noise characteristics. In low phase noise design guessing isnt good enough, actual measurements are required for verification. Whilst it is relatively easy to filter out high frequency power supply noise, filtering out low frequency noise is much more difficult. Single ended circuits (most RF circuits) have little or no inherent power supply rejection and they are particularly susceptible to phase noise generated by power supply noise modulating the RF circuit's phase shift. Bruce ___ 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.
