[time-nuts] Ground loops in measurements?
Moin, A couple of weeks ago, there was a short discussion on "bad" connectors and cables and the coupled in noise of those. Summarized it said that measurements in the time-nuts scale are very sensitive to even the lowest noise levels and coupled in signals. But, all the measurements we do are done using some sort of coax which have their shield connected to the case of the devices. As the invovled devices in a measurement are also grounded over their power supply this will lead to ground loops and thus a 50/60Hz noise. Also, because loops are good magnetic antennas, a lot of other noise floating around in the ether is coupled in (eg a nearby radio station). How do you handle this kind of problems? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] Ground loops in measurements?
50, paul swed wrote: >> > >> > ___ >> > 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. >> > -- Message: 2 Date: Mon, 20 May 2013 06:14:12 -0700 From: Jim Lux To: time-nuts@febo.com Subject: Re: [time-nuts] time transfer over USB Message-ID: <519a21a4.8020...@earthlink.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 5/20/13 2:43 AM, Attila Kinali wrote: > Oh.. and connect the whole thing to a port on the PC that does _not_ > have an internal USB hub. > That's a bit of challenge, I suspect.. A casual look at the PCs I have around here running windows all seem to have on-mobo hubs when you check Device Manager. I suspect they are integrated into one of the peripheral chips. -- Message: 3 Date: Mon, 20 May 2013 06:17:23 -0700 From: "Tom Van Baak" To: "Discussion of precise time and frequency measurement" Subject: Re: [time-nuts] Time Nut Pickens at the MIT Flea ? Message-ID: Content-Type: text/plain; charset="iso-8859-1" A gentle reminder to keep postings to time-nuts as technical as possible, and on-topic. The occasional mention of upcoming local events or conferences is welcome (it's a great way to build community), but I suggest subsequent details, follow-up, meeting arrangements, and where to get pizza should be done by private email. The list now has 1300 members world-wide. Thanks, /tvb http://leapsecond.com/time-nuts.htm -- Message: 4 Date: Mon, 20 May 2013 14:06:08 + From: li...@lazygranch.com To: "Discussion of precise time and frequency measurement" Subject: Re: [time-nuts] time transfer over USB Message-ID: <89993712-1369058767-cardhu_decombobulator_blackberry.rim.net-179398076-@b26.c1.bise6.blackberry> Content-Type: text/plain I suspect the idea is to use a port where no other devices, that is internal, are on the hub. Like you, I never saw a usb port not on a hub. -Original Message- From: Jim Lux Sender: time-nuts-boun...@febo.com Date: Mon, 20 May 2013 06:14:12 To: Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] time transfer over USB On 5/20/13 2:43 AM, Attila Kinali wrote: > Oh.. and connect the whole thing to a port on the PC that does _not_ > have an internal USB hub. > That's a bit of challenge, I suspect.. A casual look at the PCs I have around here running windows all seem to have on-mobo hubs when you check Device Manager. I suspect they are integrated into one of the peripheral chips. ___ 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. -- Message: 5 Date: Mon, 20 May 2013 16:15:00 +0200 From: Volker Esper To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ground loops in measurements? Message-ID: <519a2fe4.8090...@t-online.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Moin Attila, yes ground loops can cause serious measurement problems. And solving those could fill a hole book. Here's what I do in practical: 1.) avoid the loop 2.) if you can't, try harder to avoid it - depending on the problem: break up the dc loop by using capacitors (most often you only need to kill 50/60 Hz so you can possibly insert a C in the shield) - if you need dc current or extremly low frequencies flowing in the shield, use inductors in the shield to get rid of 50/60 Hz - if you have to transfer low frequency rectangular pulses, you have to decide or even to try, what will be the better choice - but that induces new problems if you have to be synchronous to within some ns... - on the lab bench - if you can't avoid loops - make the area of the loop as small as you can to reduce the inducing field -> keep shields together - use a well grounded!! metal plate (use iron, if you can) under your experiment and lay the coax cables flat down on it - as far as you can connect all case grounds at one point only - if you are experimenting with low frequency on your bench you can try to not connect the shield on one side of the cable - be aware, that the current now takes another way, so tha
Re: [time-nuts] Ground loops in measurements?
Moin Attila, yes ground loops can cause serious measurement problems. And solving those could fill a hole book. Here's what I do in practical: 1.) avoid the loop 2.) if you can't, try harder to avoid it - depending on the problem: break up the dc loop by using capacitors (most often you only need to kill 50/60 Hz so you can possibly insert a C in the shield) - if you need dc current or extremly low frequencies flowing in the shield, use inductors in the shield to get rid of 50/60 Hz - if you have to transfer low frequency rectangular pulses, you have to decide or even to try, what will be the better choice - but that induces new problems if you have to be synchronous to within some ns... - on the lab bench - if you can't avoid loops - make the area of the loop as small as you can to reduce the inducing field -> keep shields together - use a well grounded!! metal plate (use iron, if you can) under your experiment and lay the coax cables flat down on it - as far as you can connect all case grounds at one point only - if you are experimenting with low frequency on your bench you can try to not connect the shield on one side of the cable - be aware, that the current now takes another way, so that is practicable in only few situations (and if you fumble around it will change measurement conditions) - use floating power supplies - but remember, they can be coupled to earth or the power line over the stray capacitance of the transformer (rather a problem for higher frequencies than 50/60 Hz) Volker Am 20.05.2013 14:08, schrieb Attila Kinali: Moin, A couple of weeks ago, there was a short discussion on "bad" connectors and cables and the coupled in noise of those. Summarized it said that measurements in the time-nuts scale are very sensitive to even the lowest noise levels and coupled in signals. But, all the measurements we do are done using some sort of coax which have their shield connected to the case of the devices. As the invovled devices in a measurement are also grounded over their power supply this will lead to ground loops and thus a 50/60Hz noise. Also, because loops are good magnetic antennas, a lot of other noise floating around in the ether is coupled in (eg a nearby radio station). How do you handle this kind of problems? Attila Kinali ___ 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] Ground loops in measurements?
Anyone who is serious about Time and Freq has run into ground loop problems, and finding a solution is often more "Art then Science" A common solution is star grounding, Another approach is grid work grounding, another possible solution is to isolate each instrument. Most often some trial and error is required, and nothing is as valuable as the intuition that comes from years of experience. As you experiment, documenting each change can often help not only towards a immediate solution, but also if problems arise from future changes in your system. Thomas Knox > Date: Mon, 20 May 2013 14:08:03 +0200 > From: att...@kinali.ch > To: time-nuts@febo.com > Subject: [time-nuts] Ground loops in measurements? > > Moin, > > A couple of weeks ago, there was a short discussion on "bad" connectors > and cables and the coupled in noise of those. Summarized it said that > measurements in the time-nuts scale are very sensitive to even the lowest > noise levels and coupled in signals. > > But, all the measurements we do are done using some sort of coax which > have their shield connected to the case of the devices. As the invovled > devices in a measurement are also grounded over their power supply > this will lead to ground loops and thus a 50/60Hz noise. Also, because > loops are good magnetic antennas, a lot of other noise floating around > in the ether is coupled in (eg a nearby radio station). > > How do you handle this kind of problems? > > Attila Kinali > > -- > The people on 4chan are like brilliant psychologists > who also happen to be insane and gross. > -- unknown > ___ > 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] Ground loops in measurements?
Hi Coax is interesting stuff. The shielding is only good down to some lower frequency limit. For anything practical that's going to be > 100 KHz. At the frequencies you *should* use coax at, transformer coupling is the easy way to break the ground loop. In this era of cell phones all over the place, a transformer plus some sort of common mode choke is the standard approach. For things like 1 pps, you should be using some sort of balanced transmission. Twisted pair, or better, shielded twisted pair. You can either run into a balanced receiver IC and dc couple or into a transformer and do something a bit fancier. With the IC you have a maximum voltage offset that can be tolerated. With the transformer you have the cost / delay / possible error in picking up the edges. If your environment is noisy enough, you may have to transport your pps on some sort of carrier. RF and optical both have their fans. None of that is going to be easy. The alternative is to do what you would do in a screen room. Single point ground, everything tied tightly together. Put reasonable filtering on everything in and out. Tie the filters to the common ground point. This also is not easy, but possibly not as hard as redesigning the ins and outs of every box in sight. I have seen this approach used on some *very* large systems. A some what extreme approach (that I have seen used). Forget about all the shielding and stuff. Buy a farm, put up a small metal shack in the middle of a large field. Bring a hand cart with batteries. Run everything on a big copper covered table. Lots of ways to go. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: Monday, May 20, 2013 8:08 AM To: time-nuts@febo.com Subject: [time-nuts] Ground loops in measurements? Moin, A couple of weeks ago, there was a short discussion on "bad" connectors and cables and the coupled in noise of those. Summarized it said that measurements in the time-nuts scale are very sensitive to even the lowest noise levels and coupled in signals. But, all the measurements we do are done using some sort of coax which have their shield connected to the case of the devices. As the invovled devices in a measurement are also grounded over their power supply this will lead to ground loops and thus a 50/60Hz noise. Also, because loops are good magnetic antennas, a lot of other noise floating around in the ether is coupled in (eg a nearby radio station). How do you handle this kind of problems? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] Ground loops in measurements?
Hi Bob whats the problem at low freqs ?? I thought leakage was a function of the size of the "holes"v the wavelengthor are we into braid skin effect below 100kHz?? so as not to drag this OT a reference will suffice in answer. Best Wishes Alan G3NYK - Original Message - From: "Bob Camp" To: "'Discussion of precise time and frequency measurement'" Sent: Monday, May 20, 2013 6:00 PM Subject: Re: [time-nuts] Ground loops in measurements? Hi Coax is interesting stuff. The shielding is only good down to some lower frequency limit. For anything practical that's going to be > 100 KHz. At the frequencies you *should* use coax at, transformer coupling is the easy way to break the ground loop. In this era of cell phones all over the place, a transformer plus some sort of common mode choke is the standard approach. For things like 1 pps, you should be using some sort of balanced transmission. Twisted pair, or better, shielded twisted pair. You can either run into a balanced receiver IC and dc couple or into a transformer and do something a bit fancier. With the IC you have a maximum voltage offset that can be tolerated. With the transformer you have the cost / delay / possible error in picking up the edges. If your environment is noisy enough, you may have to transport your pps on some sort of carrier. RF and optical both have their fans. None of that is going to be easy. The alternative is to do what you would do in a screen room. Single point ground, everything tied tightly together. Put reasonable filtering on everything in and out. Tie the filters to the common ground point. This also is not easy, but possibly not as hard as redesigning the ins and outs of every box in sight. I have seen this approach used on some *very* large systems. A some what extreme approach (that I have seen used). Forget about all the shielding and stuff. Buy a farm, put up a small metal shack in the middle of a large field. Bring a hand cart with batteries. Run everything on a big copper covered table. Lots of ways to go. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: Monday, May 20, 2013 8:08 AM To: time-nuts@febo.com Subject: [time-nuts] Ground loops in measurements? Moin, A couple of weeks ago, there was a short discussion on "bad" connectors and cables and the coupled in noise of those. Summarized it said that measurements in the time-nuts scale are very sensitive to even the lowest noise levels and coupled in signals. But, all the measurements we do are done using some sort of coax which have their shield connected to the case of the devices. As the invovled devices in a measurement are also grounded over their power supply this will lead to ground loops and thus a 50/60Hz noise. Also, because loops are good magnetic antennas, a lot of other noise floating around in the ether is coupled in (eg a nearby radio station). How do you handle this kind of problems? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] Ground loops in measurements?
A couple of good references regarding noise minimization in electronic systems are: "Grounding and Shielding: Circuits and Interference" by Ralph Morrison & "Noise Reduction Techniques in Electronic Systems" by Henry W. Ott And the old fallback has been MIL-HDB-419 volumes I and II which mostly addresses facility installation but does provide some insight to good grounding practices for same. If you do have in interest in facilities grounding, the Verizon Plant Practices manuals (which are sometimes found on the Web) are also good as is the Motorola R56 installation standard. My references were mainly the two books by Morrison (best) and Ott when I was designing and building astronomical instrumentation where we had to get our detector noise levels down below 10 electrons when measuring light levels from stars. Greg This message was sent using IMP, the Internet Messaging Program. ___ 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] Ground loops in measurements?
Hi The braid becomes less effective at lower frequencies due to skin effect. Once that happens you have a magnetic loop that is not as effective at rejecting signals as a twisted pair. Looking at it another way, the threat signal is induced on the shield (braid) and it penetrates to couple to the center conductor. There are a couple of other ways to look at it, they all ultimately come back to the same point. There are a few other odd things that happen as well as you drop frequency, none of them really very helpful for moving signals. --- Now - is it actually a problem or not? As always, that depends. Most of the nasty stuff in a 1 pps is in the edges. That energy (with a fast edge) is nicely captured by the coax. The low frequency stuff is not captured as well, but it also doesn't couple all that well either. Making a transformer work to 1 Hz isn't very easy. So, coax is fine for getting the signal to it's destination. It's only when you look at the ground loops and threat signals that there could be an issue. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Alan Melia Sent: Monday, May 20, 2013 2:50 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ground loops in measurements? Hi Bob whats the problem at low freqs ?? I thought leakage was a function of the size of the "holes"v the wavelengthor are we into braid skin effect below 100kHz?? so as not to drag this OT a reference will suffice in answer. Best Wishes Alan G3NYK - Original Message - From: "Bob Camp" To: "'Discussion of precise time and frequency measurement'" Sent: Monday, May 20, 2013 6:00 PM Subject: Re: [time-nuts] Ground loops in measurements? > Hi > > Coax is interesting stuff. The shielding is only good down to some lower > frequency limit. For anything practical that's going to be > 100 KHz. > > At the frequencies you *should* use coax at, transformer coupling is the > easy way to break the ground loop. In this era of cell phones all over the > place, a transformer plus some sort of common mode choke is the standard > approach. > > For things like 1 pps, you should be using some sort of balanced > transmission. Twisted pair, or better, shielded twisted pair. You can > either > run into a balanced receiver IC and dc couple or into a transformer and do > something a bit fancier. With the IC you have a maximum voltage offset > that > can be tolerated. With the transformer you have the cost / delay / > possible > error in picking up the edges. > > If your environment is noisy enough, you may have to transport your pps on > some sort of carrier. RF and optical both have their fans. > > None of that is going to be easy. The alternative is to do what you would > do > in a screen room. Single point ground, everything tied tightly together. > Put > reasonable filtering on everything in and out. Tie the filters to the > common > ground point. This also is not easy, but possibly not as hard as > redesigning > the ins and outs of every box in sight. I have seen this approach used on > some *very* large systems. > > A some what extreme approach (that I have seen used). Forget about all the > shielding and stuff. Buy a farm, put up a small metal shack in the middle > of > a large field. Bring a hand cart with batteries. Run everything on a big > copper covered table. > > Lots of ways to go. > > Bob > > > > -----Original Message- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Attila Kinali > Sent: Monday, May 20, 2013 8:08 AM > To: time-nuts@febo.com > Subject: [time-nuts] Ground loops in measurements? > > Moin, > > A couple of weeks ago, there was a short discussion on "bad" connectors > and cables and the coupled in noise of those. Summarized it said that > measurements in the time-nuts scale are very sensitive to even the lowest > noise levels and coupled in signals. > > But, all the measurements we do are done using some sort of coax which > have their shield connected to the case of the devices. As the invovled > devices in a measurement are also grounded over their power supply > this will lead to ground loops and thus a 50/60Hz noise. Also, because > loops are good magnetic antennas, a lot of other noise floating around > in the ether is coupled in (eg a nearby radio station). > > How do you handle this kind of problems? > > Attila Kinali > > -- > The people on 4chan are like brilliant psychologists > who also happen to be insane and gross. > -- unknown > ___ > time-nuts mailing list -- time-nuts@febo.com
Re: [time-nuts] Ground loops in measurements?
t. Regards Paul WB8TSL On Sun, May 19, 2013 at 10:09 PM, Bob Bownes wrote: We should plan a Time-Nuts BOF lunch after the next flea. Saw little TN gear @ Dayton save one Efretom RBI time base for $1800 and a few 10811s of dubious quality for $50 ea. the dents put me off gambling on one since I was given or the afternoon before! ;) On May 19, 2013, at 21:50, paul swed wrote: ___ 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. -- Message: 2 Date: Mon, 20 May 2013 06:14:12 -0700 From: Jim Lux To: time-nuts@febo.com Subject: Re: [time-nuts] time transfer over USB Message-ID:<519a21a4.8020...@earthlink.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 5/20/13 2:43 AM, Attila Kinali wrote: Oh.. and connect the whole thing to a port on the PC that does _not_ have an internal USB hub. That's a bit of challenge, I suspect.. A casual look at the PCs I have around here running windows all seem to have on-mobo hubs when you check Device Manager. I suspect they are integrated into one of the peripheral chips. -- Message: 3 Date: Mon, 20 May 2013 06:17:23 -0700 From: "Tom Van Baak" To: "Discussion of precise time and frequency measurement" Subject: Re: [time-nuts] Time Nut Pickens at the MIT Flea ? Message-ID: Content-Type: text/plain; charset="iso-8859-1" A gentle reminder to keep postings to time-nuts as technical as possible, and on-topic. The occasional mention of upcoming local events or conferences is welcome (it's a great way to build community), but I suggest subsequent details, follow-up, meeting arrangements, and where to get pizza should be done by private email. The list now has 1300 members world-wide. Thanks, /tvb http://leapsecond.com/time-nuts.htm -- Message: 4 Date: Mon, 20 May 2013 14:06:08 + From: li...@lazygranch.com To: "Discussion of precise time and frequency measurement" Subject: Re: [time-nuts] time transfer over USB Message-ID: <89993712-1369058767-cardhu_decombobulator_blackberry.rim.net-179398076-@b26.c1.bise6.blackberry> Content-Type: text/plain I suspect the idea is to use a port where no other devices, that is internal, are on the hub. Like you, I never saw a usb port not on a hub. -Original Message- From: Jim Lux Sender: time-nuts-boun...@febo.com Date: Mon, 20 May 2013 06:14:12 To: Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] time transfer over USB On 5/20/13 2:43 AM, Attila Kinali wrote: Oh.. and connect the whole thing to a port on the PC that does _not_ have an internal USB hub. That's a bit of challenge, I suspect.. A casual look at the PCs I have around here running windows all seem to have on-mobo hubs when you check Device Manager. I suspect they are integrated into one of the peripheral chips. ___ 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. -- Message: 5 Date: Mon, 20 May 2013 16:15:00 +0200 From: Volker Esper To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ground loops in measurements? Message-ID:<519a2fe4.8090...@t-online.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Moin Attila, yes ground loops can cause serious measurement problems. And solving those could fill a hole book. Here's what I do in practical: 1.) avoid the loop 2.) if you can't, try harder to avoid it - depending on the problem: break up the dc loop by using capacitors (most often you only need to kill 50/60 Hz so you can possibly insert a C in the shield) - if you need dc current or extremly low frequencies flowing in the shield, use inductors in the shield to get rid of 50/60 Hz - if you have to transfer low frequency rectangular pulses, you have to decide or even to try, what will be the better choice - but that induces new problems if you have to be synchronous to within some ns... - on the lab bench - if you can't avoid loops - make the area of the loop as small as you can to reduce the inducing field -> keep shields together - use a well grounded!! metal plate (use iron, if you can) under your experiment and lay the coax cables flat down on it - as far as you can connect all case grounds at one point only - if you are experimenting with low frequency on your
Re: [time-nuts] Ground loops in measurements?
I will try to avoid too much repetition of what has already been posted. Some other ways I have handled ground loops: 1. Capacitive or inductive coupling - this may include AC coupling in *both* the center conductor and shield of a coaxial cable. 2. High isolation power supplies - these may use special transformers which include a large air gap to reduce capacitive coupling. In extreme applications, they can also be implemented using ceramic transducers. A less expensive way is to implement a small high frequency inverter using a torroidal transformer with well separated windings; Tektronix liked to do this and I have a number of older DMMs that use this for isolation of their floating inputs. 3. Some instruments implement isolation internally and use connectors which are isolated from chassis ground. The Tektronix PG506 pulse generator is a good example of this. 10Base-2 used isolated BNC connectors and an isolated power supply. 4. USB is a major and sometimes destructive problem with its shield and signal ground connection between instruments. USB isolated hubs are available and Analog Devices even makes an ASIC for this now. Ethernet is pretty good in this respect. One reason I have always liked RS-232 is that it was relatively easy to isolate. The old MIDI standard uses optical isolation as part of the standard. 5. One trick you can find inside test instrumentation is the use of common mode chokes (current baluns) on transmission lines between modules. The same thing can be done externally. 6. Instrumentation amplifiers can be used in place of transformers for isolation in some cases. Differential inputs can be very handy to prevent ground loops even from single ended sources. 7. One trick I have used at lower frequencies is to use currents instead of voltages (transconductance outputs) with resistive terminations at the endpoint and the coax only grounded at one end. This also works across a ground plain when ground currents would otherwise corrupt precision like maybe if you were driving the control voltage input of an OCXO. 8. Differential oscilloscopes probes are very handy for tracking down ground loops. I really like my Tektronix 7A13 and 7A22 differential amplifiers for this. 9. If you are making a normal single ended measurement with an oscilloscope probe, measure the point where the ground clip is attached; if the signal is not flat, then you have a ground loop. ___ 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.
