Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output - around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
--
Christopher Howard
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
On Wed, 19 Feb 2025 09:35:52 -0900, Christopher Howard <christopher@librehacker.com> wrote:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy >that would somehow pick up less ambient noise.
I assume that your "leads" are a coax.
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
Common-mode chokes, ferrites or toroids, can help. Just plugging the generator and the scope into the same outlet may help.
I assume that your "leads" are a coax.
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
Common-mode chokes, ferrites or toroids, can help. Just plugging the generator and the scope into the same outlet may help.
What sort of noise and at what sorts of frequency?
How much of each lead (signal and gnd/return) is "exposed"
outside of the shield?
Frequency??
Martin Brown <'''newspam'''@nonad.co.uk> writes:
What sort of noise and at what sorts of frequency?
Looking at in on the scope, the noise is thick, like a solid bar of
spikes around the real signal. When I zoom in on it, it seems like it
has a beat of around 40 Khz.
Martin Brown <'''newspam'''@nonad.co.uk> writes:> What sort of noise and at what sorts of frequency?Looking at in on the scope, the noise is thick, like a solid bar ofspikes around the real signal. When I zoom in on it, it seems like ithas a beat ofaround 40 Khz.-- Christopher Howard
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
John Larkin <jjlarkin@highlandtechnology.com> writes:
I assume that your "leads" are a coax.
Yes, the loads something my co-worker threw together from old cable
laying around. One one side is BNC that plugs into the signal generator. After than is a thin coax about 3mm thick. At the other end, he split
the inner conductor and the shield into two leads, one with a pin at the
end, and one with an alligator lead.
Martin Brown <'''newspam'''@nonad.co.uk> writes:
What sort of noise and at what sorts of frequency?
Looking at in on the scope, the noise is thick, like a solid bar of
spikes around the real signal. When I zoom in on it, it seems like it
has a beat of around 40 Khz.
John Larkin <jjlarkin@highlandtechnology.com> writes:
I assume that your "leads" are a coax.
Yes, the loads something my co-worker threw together from old cable
laying around. One one side is BNC that plugs into the signal generator. >After than is a thin coax about 3mm thick. At the other end, he split
the inner conductor and the shield into two leads, one with a pin at the
end, and one with an alligator lead.
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
I have a project I'm doing building my own analog computer — which
currently does not have any filtering installed on it, other than some
100 nF bypass caps. I can see this heavy noise — about .6 mV p-p — on
all signal output, regardless of what op amp I tap into. If I remove the >analog computer and just tie the signal generator to the scope, I see
the same noise.
If I turn the computers off around my workbench, the noise becomes less, >proportional to the percentage of computers I turn off. If I take the
signal generator and the computer into another room with no computers,
the noise almost vanishes.
Common-mode chokes, ferrites or toroids, can help. Just plugging the
generator and the scope into the same outlet may help.
I am planning to go that route, with the chokes and such, once some
parts come in. But I was also wondering about the single leads
themselves, which feed from the signal generator into analog computer
inputs.
On 20/02/2025 5:35 am, Christopher Howard wrote:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output - around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
You might think about double shielded coax.The standard woven braid outer offers about 98% shielding and adding a wrap of
aluminised Mylar underneath it get you closer to 100% shielding.
As other posts have pointed out, your problem is probably going to be earth loops, and wrapping a short length of the coax around
a ferrite toroid can help with that. Ralph Morrison wrote the book on the subject back in 1967. I read the first edition back
then, and I've had access to most of the subsequent editions. I've got the fourth edition from 1998 when I finally had to buy my
own copy.
https://books.google.com.au/books/about/Grounding_and_Shielding_Techniques_in_In.html?id=IxUjAAAAMAAJ&redir_esc=y\
The 40kHz periodicity suggests that old cheap switching power supplies are the source of the noise.
--
Bill Sloman, Sydney
John Larkin <jjlarkin@highlandtechnology.com> writes:
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
I have a project I'm doing building my own analog computer — which currently does not have any filtering installed on it, other than some
100 nF bypass caps. I can see this heavy noise — about .6 mV p-p — on
all signal output, regardless of what op amp I tap into. If I remove the analog computer and just tie the signal generator to the scope, I see
the same noise.
If I turn the computers off around my workbench, the noise becomes less, proportional to the percentage of computers I turn off. If I take the
signal generator and the computer into another room with no computers,
the noise almost vanishes.
Common-mode chokes, ferrites or toroids, can help. Just plugging the
generator and the scope into the same outlet may help.
I am planning to go that route, with the chokes and such, once some
parts come in. But I was also wondering about the single leads
themselves, which feed from the signal generator into analog computer
inputs.
John Larkin <jjlarkin@highlandtechnology.com> writes:
I assume that your "leads" are a coax.
Yes, the loads something my co-worker threw together from old cable
laying around. One one side is BNC that plugs into the signal generator. After than is a thin coax about 3mm thick. At the other end, he split
the inner conductor and the shield into two leads, one with a pin at the
end, and one with an alligator lead.
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
I have a project I'm doing building my own analog computer - which
currently does not have any filtering installed on it, other than some
100 nF bypass caps. I can see this heavy noise - about .6 mV p-p - on
all signal output, regardless of what op amp I tap into. If I remove the analog computer and just tie the signal generator to the scope, I see
the same noise.
If I turn the computers off around my workbench, the noise becomes less, proportional to the percentage of computers I turn off. If I take the
signal generator and the computer into another room with no computers,
the noise almost vanishes.
Common-mode chokes, ferrites or toroids, can help. Just plugging the
generator and the scope into the same outlet may help.
I am planning to go that route, with the chokes and such, once some
parts come in. But I was also wondering about the single leads
themselves, which feed from the signal generator into analog computer
inputs.
--
Christopher Howard
The next test is to unclip the croc-clip and measure the resistance
from the chassis of the device-on-test (or the 'scope) to the sig-gen
earth. If it is low, that means there is an alternative D,C. signal
path in parallel with the screen of the co-ax, which could be picking
up interference.
If the D.C. test appears satisfactory, there may be an A.C. path
through mains suppression capacitors, which passes the interference
but doesn't showwith the D.C. of a continuity test. Does the signal
drop and the interference get worse when the croc-clip is unclipped?
If the signal doesn't drop, you have an A.C. path in parallel with the
earth.
Do similar checks on the 'scope earth lead. .
Does it look like a PWM square wave or a sine wave?
I only ever see ripple if I stick my finger on an probe and my
environment is really rather electrically noisy.
You haven't got one of those ultrasonic humidifiers nearby?
What happens if you put a 0.1uF capacitor in series with the coax
shield coax so that there can be no DC current flow on the earth
connection?
Sigh. What is the frequency of the *desired* signal?
If you make your signals balanced differential drive then you can
withstand a lot of ambient common mode noise without problems. The way
that instrumentation amplifiers do it.
IOW rather than coax you have two signal lines v+ and v- inside a
passive conductive outer shield that plays no part in the signal transmission. It is there only as a Faraday shield against external interference.
I think there is something funny going on with your setup.
As far as the connection from the signal generator to the analog
computer input, that doesn't sound too hard. But with a quick search on
the Internet, it seems that balanced cables are not made with BNC
connectors on one end, to match the signal generator. Do you know of an adapter that would work for this?
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp6drd$2mqf1$1@dont-email.me...
On 20/02/2025 5:35 am, Christopher Howard wrote:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output - around
600 mV p-p. I am wondering if there are any particular leads I could buy >>> that would somehow pick up less ambient noise.
You might think about double shielded coax.The standard woven braid outer offers about 98% shielding and adding a wrap of
aluminised Mylar underneath it get you closer to 100% shielding.
As other posts have pointed out, your problem is probably going to be earth loops, and wrapping a short length of the coax around
a ferrite toroid can help with that. Ralph Morrison wrote the book on the subject back in 1967. I read the first edition back
then, and I've had access to most of the subsequent editions. I've got the fourth edition from 1998 when I finally had to buy my
own copy.
https://books.google.com.au/books/about/Grounding_and_Shielding_Techniques_in_In.html?id=IxUjAAAAMAAJ&redir_esc=y\
The sixth edition (2016) appears to be called
Grounding and Shielding: Circuits and Interference.
And is not hard to obtain.
But unless you want to wade through a book which touches on the calculus of electromagnetic theory (and it's perfectly fine if you
do), you're likely better off focussing on the practical side of things.
Decades ago before anything like mobile phones existed I worked at a newly constructed facility which had a powerful radio
transmitter.
The gatehouse was outside the facility and had a PA (Public Address) system installed for communication with people inside the
facility.
When keying the microphone you could hear nothing inside the facility other than the transmitter modulation.
It took many weeks to solve the problem and more than a few people (possibly with PhD level qualifications) demonstrated their lack
of knowledge by proposing solutions such as ferrite toroids in the speaker wiring (100V line system).
Eventually the problem was solved as follows.
Remove the preamplifier board from the all in one pre amp/power amp unit in the gatehouse.
Obtain one metal box of suitable size and drill holes for suitable feedthrough capacitors for all connections.
https://www.google.com/search?&q=feedthrough+capacitor&udm=2
Mount the board in the box and connect to the feedthrough capacitors as necessary. Close the box.
Glue the box to the back of the pre amp/power amp unit.
Wire from the feedthrough capacitors to the appropriate points in the unit. The PA was now totally quiet, except for the announcement being made.
The 40kHz periodicity suggests that old cheap switching power supplies are the source of the noise.
Christopher Howard <christopher@librehacker.com> writes:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
WWV used to be located in Greenbelt MD. But their neighbor,
NASA-GSFC got tired of the 5, 10, 15MHZ, etc. being on every
scope. WWV got moved to the wilds outside of Ft. Collins CO.
liz@poppyrecords.invalid.invalid (Liz Tuddenham) writes:
Checking just now, continuity from sig-gen earth to croc-clip appears to
be good.
The next test is to unclip the croc-clip and measure the resistance
from the chassis of the device-on-test (or the 'scope) to the sig-gen earth. If it is low, that means there is an alternative D,C. signal
path in parallel with the screen of the co-ax, which could be picking
up interference.
I'm a little fuzzy on how to do this test, as the DUT does not have a
chassis (all on breadboards) and the scope is fully encased in plastic, except for the probe ports and such.
But if I connect just the signal pin to the DUT, leave the alligator
clip disconnected, and then measure from DUT gnd bar to sig-gen earth,
it is infinite resistance.
If the D.C. test appears satisfactory, there may be an A.C. path
through mains suppression capacitors, which passes the interference
but doesn't showwith the D.C. of a continuity test. Does the signal
drop and the interference get worse when the croc-clip is unclipped?
If the signal doesn't drop, you have an A.C. path in parallel with the earth.
For this test, I put the signal generator leads in as input to DUT and
scope as output from DUT. When I remove the crop clip from DUT gnd, the sinusoidal signal is still visible on the scope at the same amplitude,
but the noise surrounding it increases in amplitude significantly.
Do similar checks on the 'scope earth lead. .
Once again, the sine signal is still visible on the scope at the same amplitude, but the noise surrounding it increases — even more
dramatically.
If you make your signals balanced differential drive then you can
withstand a lot of ambient common mode noise without problems. The way
that instrumentation amplifiers do it.
I'm interested in this idea, though I'm not sure how to apply this in
any practical way to the connections inside the analog computer, i.e.,
the patches between the different integrators and such.
As far as the connection from the signal generator to the analog
computer input, that doesn't sound too hard. But with a quick search on
the Internet, it seems that balanced cables are not made with BNC
connectors on one end, to match the signal generator. Do you know of an adapter that would work for this?
For the differential receiver, do I need anything special for this, or
can I just feed the conductors into an LF356 op amp (unity gain configuration...?)
IOW rather than coax you have two signal lines v+ and v- inside a
passive conductive outer shield that plays no part in the signal
transmission. It is there only as a Faraday shield against external
interference.
Any particular cable you recommend?
I think there is something funny going on with your setup.
I don't know of anything "funny" but am still learning. This is
certainly a DIY, learn-as-you-go project. For the analog computer, I'm largely following the Grappendorf schematics, though building it on a breadboard instead of printing the PCBs, which I can't afford right now.
https://www.grappendorf.net/projects/analog-computer/
Some other substitutions I have made: I haven't built a PS as I happen
to have access to a bipolar 15V supply already, though admittedly it is
a rather old unit. I also haven't built the reference voltage module but
am hoping to have parts for that in the next few weeks.
Frequency??
I'm not sure exactly, but when I zoom in to it on the scope, the noise appeared to have a regular ebb and flow of about 40 Khz.
Christopher Howard <christopher@librehacker.com> wrote:
Frequency??
I'm not sure exactly, but when I zoom in to it on the scope, the noise
appeared to have a regular ebb and flow of about 40 Khz.
That seems very likely to be from some power supply, either wall wart or built into some equipment.
A great EMI sniffer to sleuth out is an old school $5 pocket AM broadcast radio (the kind slightly larger than a cigarette pack and powered by 2 AA
or 9v block battery).
--
piglet
Those boards don't look at all sophisticated. When you say building it
on breadboards do you mean Vero board or some other soldered
prototyping medium or do you mean literally on a plug in patchboard?
Have you checked that your bipolar 15v supply isn't the noise source?
The noise you are describing at around 40kHz looks awfully like an old
school switched mode PSU sort of frequency.
On 21/02/2025 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp6drd$2mqf1$1@dont-email.me...
On 20/02/2025 5:35 am, Christopher Howard wrote:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on >>>> the long leads coming out of the signal generator BNC output - around
600 mV p-p. I am wondering if there are any particular leads I could buy >>>> that would somehow pick up less ambient noise.
You might think about double shielded coax.The standard woven braid outer offers about 98% shielding and adding a wrap of
aluminised Mylar underneath it get you closer to 100% shielding.
As other posts have pointed out, your problem is probably going to be earth loops, and wrapping a short length of the coax
around
a ferrite toroid can help with that. Ralph Morrison wrote the book on the subject back in 1967. I read the first edition back
then, and I've had access to most of the subsequent editions. I've got the fourth edition from 1998 when I finally had to buy my
own copy.
https://books.google.com.au/books/about/Grounding_and_Shielding_Techniques_in_In.html?id=IxUjAAAAMAAJ&redir_esc=y\
The sixth edition (2016) appears to be called
Grounding and Shielding: Circuits and Interference.
And is not hard to obtain.
But unless you want to wade through a book which touches on the calculus of electromagnetic theory (and it's perfectly fine if
you
do), you're likely better off focussing on the practical side of things.
Wrong.
Ralph Morrison's book is sublimely practical; it includes enough electromagnetic theory to let you understand what is going on.
Cook-book style texts don't, and should be avoided.
Decades ago before anything like mobile phones existed I worked at a newly constructed facility which had a powerful radio
transmitter.
The gatehouse was outside the facility and had a PA (Public Address) system installed for communication with people inside the
facility.
When keying the microphone you could hear nothing inside the facility other than the transmitter modulation.
It took many weeks to solve the problem and more than a few people (possibly with PhD level qualifications) demonstrated their
lack
of knowledge by proposing solutions such as ferrite toroids in the speaker wiring (100V line system).
Eventually the problem was solved as follows.
Remove the preamplifier board from the all in one pre amp/power amp unit in the gatehouse.
Obtain one metal box of suitable size and drill holes for suitable feedthrough capacitors for all connections.
https://www.google.com/search?&q=feedthrough+capacitor&udm=2
Mount the board in the box and connect to the feedthrough capacitors as necessary. Close the box.
Glue the box to the back of the pre amp/power amp unit.
Wire from the feedthrough capacitors to the appropriate points in the unit. >> The PA was now totally quiet, except for the announcement being made.
Ralph Morrison talks quite a lot about double-screened transformers, which help when where enough current is being injected into
the screen on one side to produce the significant voltage drops across the screen.
Powerful radio transmitters do produce quite intense electric fields. You have to put Faraday cages around fluorescent lights to
stop them lighting up even when they are switched off.
Back in the days when you'd build a preamplifier board on two layer printed card without any kind of ground plane, you would have
had to screen it carefully.
When I was working at Cambridge Instruments a number of old two layer boards were re-worked as four and six layer boards with
buried ground planes, and we could leave out the aluminium screening plates we'd had to fit to stop adjacent boards in our racks
from messing up their neighbours.
The 40kHz periodicity suggests that old cheap switching power supplies are the source of the noise.
--
Bill Sloman, Sydney
Those boards don't look at all sophisticated. When you say building it
on breadboards do you mean Vero board or some other soldered
prototyping medium or do you mean literally on a plug in patchboard?
I'm use the common white breadboards where you push the leads and
components in. I'm not sure what the technical term is for those.
Have you checked that your bipolar 15v supply isn't the noise source?
The noise you are describing at around 40kHz looks awfully like an old
school switched mode PSU sort of frequency.
I checked just now, but the noise is not affected at all by turn on or
off the bipolar 15 volt supply. As mentioned earlier, turning off
computers at the desk, especially one older computer, eliminates most of
the noise.
--
Christopher Howard
I wanted to mention that this morning I moved the old PC computer box
about ten feet away from my work station, and that reduced the noise
down immediately to about 100 mV p-p, from the original 500 mV p-p.
After doing that, I tried running the signal from the signal generator through a simple lowpass RC filter, with R=200? and C=1µF. This drops
the noise down some more to about 40 mV p-p.
I also moved the signal generator closer and am using some very short
leads with alligator clips. This doesn't seem to have much effect on the noise, as far as I tell, but it seemed like a good idea in principle.
I like the idea of putting my analog computer inside a metal box, but I
don't currently have a spare metal box, and also that would hide all the switches, trim pots, and terminals. I have an idea though of moving this direction later after building some kind of patch panel. I also wonder
if it might be helpful at least to have the bottoms and sides of the
analog computer surrounded by metal, i.e., set it inside an open metal
box.
--
Christopher Howard
I wanted to mention that this morning I moved the old PC computer box
about ten feet away from my work station, and that reduced the noise
down immediately to about 100 mV p-p, from the original 500 mV p-p.
After doing that, I tried running the signal from the signal generator >through a simple lowpass RC filter, with R=200? and C=1µF. This drops
the noise down some more to about 40 mV p-p.
I also moved the signal generator closer and am using some very short
leads with alligator clips. This doesn't seem to have much effect on the >noise, as far as I tell, but it seemed like a good idea in principle.
I like the idea of putting my analog computer inside a metal box, but I
don't currently have a spare metal box, and also that would hide all the >switches, trim pots, and terminals. I have an idea though of moving this >direction later after building some kind of patch panel. I also wonder
if it might be helpful at least to have the bottoms and sides of the
analog computer surrounded by metal, i.e., set it inside an open metal
box.
If you make your signals balanced differential drive then you can
withstand a lot of ambient common mode noise without problems. The way
that instrumentation amplifiers do it.
I'm interested in this idea, though I'm not sure how to apply this in
any practical way to the connections inside the analog computer, i.e.,
the patches between the different integrators and such.
As far as the connection from the signal generator to the analog
computer input, that doesn't sound too hard. But with a quick search on
the Internet, it seems that balanced cables are not made with BNC
connectors on one end, to match the signal generator. Do you know of an >adapter that would work for this?
For the differential receiver, do I need anything special for this, or
can I just feed the conductors into an LF356 op amp (unity gain >configuration...?)
IOW rather than coax you have two signal lines v+ and v- inside a
passive conductive outer shield that plays no part in the signal
transmission. It is there only as a Faraday shield against external
interference.
Any particular cable you recommend?
I think there is something funny going on with your setup.
I don't know of anything "funny" but am still learning. This is
certainly a DIY, learn-as-you-go project. For the analog computer, I'm >largely following the Grappendorf schematics, though building it on a >breadboard instead of printing the PCBs, which I can't afford right now.
https://www.grappendorf.net/projects/analog-computer/
Some other substitutions I have made: I haven't built a PS as I happen
to have access to a bipolar 15V supply already, though admittedly it is
a rather old unit. I also haven't built the reference voltage module but
am hoping to have parts for that in the next few weeks.
I found it essential to have a big die cast metal box with coax
connectors and low-pass feed-throughs mounted in the walls when
testing sensitive circuits. A desktop faraday cage. Plus lots of
coax cables between test equipment and the circuit within the box.
On Fri, 21 Feb 2025 11:53:44 -0900, Christopher Howard ><christopher@librehacker.com> wrote:
I found it essential to have a big die cast metal box with coax
connectors and low-pass feed-throughs mounted in the walls when
testing sensitive circuits. A desktop faraday cage. Plus lots of
coax cables between test equipment and the circuit within the box.
Could you clarify/expand on what exactly you are using for the low-pass >>feed-throughs and what that looks like? Are you talking about two
separate things on the coax and feed-throughs, or like a coax connector >>attached to an RC filter?
Google for coaxial feed through capacitors.
.<https://www.engineering.com/the-engineers-guide-to-feedthrough-capacitors/>
.<https://www.ketemicro.com/tec_info28.html>
With die cast aluminum boxes, it's best to use a nut to hold the feed
through in place, rather than a threaded hole.
One can also mount probe pin jacks and the like in the box walls.
There's lots of space.
Joe
I found it essential to have a big die cast metal box with coax
connectors and low-pass feed-throughs mounted in the walls when
testing sensitive circuits. A desktop faraday cage. Plus lots of
coax cables between test equipment and the circuit within the box.
Could you clarify/expand on what exactly you are using for the low-pass >feed-throughs and what that looks like? Are you talking about two
separate things on the coax and feed-throughs, or like a coax connector >attached to an RC filter?
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp95q9$395rh$1@dont-email.me...
On 21/02/2025 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vp6drd$2mqf1$1@dont-email.me...
On 20/02/2025 5:35 am, Christopher Howard wrote:
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on >>>>> the long leads coming out of the signal generator BNC output - around >>>>> 600 mV p-p. I am wondering if there are any particular leads I could buy >>>>> that would somehow pick up less ambient noise.
You might think about double shielded coax.The standard woven braid outer offers about 98% shielding and adding a wrap of
aluminised Mylar underneath it get you closer to 100% shielding.
As other posts have pointed out, your problem is probably going to be earth loops, and wrapping a short length of the coax
around
a ferrite toroid can help with that. Ralph Morrison wrote the book on the subject back in 1967. I read the first edition back
then, and I've had access to most of the subsequent editions. I've got the fourth edition from 1998 when I finally had to buy my
own copy.
https://books.google.com.au/books/about/Grounding_and_Shielding_Techniques_in_In.html?id=IxUjAAAAMAAJ&redir_esc=y\
The sixth edition (2016) appears to be called
Grounding and Shielding: Circuits and Interference.
And is not hard to obtain.
But unless you want to wade through a book which touches on the calculus of electromagnetic theory (and it's perfectly fine if
you
do), you're likely better off focussing on the practical side of things.
Wrong.
Of course Bill. It was predictable that you'd reply like the headmaster.
I spent perhaps half an hour looking through the book you mentioned (sixth edition).
I can't quite put my finger on why, but I noticed that when talking about skin depth (Page 26, 74 and others) the word "Penetration"
is used.
This made me wonder how long it might be before I tell you what you can go do with yourself.
Ralph Morrison's book is sublimely practical; it includes enough electromagnetic theory to let you understand what is going on.
Cook-book style texts don't, and should be avoided.
Google for coaxial feed through capacitors.
.<https://www.engineering.com/the-engineers-guide-to-feedthrough-capacitors/>
.<https://www.ketemicro.com/tec_info28.html>
Joe Gwinn <joegwinn@comcast.net> writes:
Google for coaxial feed through capacitors.
.<https://www.engineering.com/the-engineers-guide-to-feedthrough-capacitors/>
.<https://www.ketemicro.com/tec_info28.html>
Thank you, I've stored these links and started looking through them.
Question: With a simple C feed through capacitor, with no resistive
element, do you have trouble with ringing? I had thought this was a
reason to use RC filters rather than just C bypass filter, to reduce/eliminate ringing.
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduceGoogle for coaxial feed through capacitors.
ringing. but enough resistance can make the resonant circuit
critically damped and the voltages and current will decay
monotonically.
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduceGoogle for coaxial feed through capacitors.
ringing. but enough resistance can make the resonant circuit
critically damped and the voltages and current will decay
monotonically.
So, when you use a coaxial feed through capacitors on your faraday cage,
do you add a resistor right after the capacitor, to reduce/eliminate
ringing? Or are you just trying that all your inputs on the board have resistors before whatever op amps or other components that they feed
into?
--
Christopher Howard
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduceGoogle for coaxial feed through capacitors.
ringing. but enough resistance can make the resonant circuit
critically damped and the voltages and current will decay
monotonically.
So, when you use a coaxial feed through capacitors on your Faraday cage,
do you add a resistor right after the capacitor, to reduce/eliminate
ringing?
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
On 26/02/2025 4:39 am, Christopher Howard wrote:
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduceGoogle for coaxial feed through capacitors.
ringing. but enough resistance can make the resonant circuit
critically damped and the voltages and current will decay
monotonically.
So, when you use a coaxial feed through capacitors on your Faraday cage,
do you add a resistor right after the capacitor, to reduce/eliminate
ringing?
The whole point about coaxial connectors is that the distributed capacitance and inductance gives you a R50R transmission line.
The only way to get "ringing" out of that is to fail to terminate the transmission line with it's characteristic impedance. In
practice it is hard to do it perfectly and you do tend to get low level reflections, but they die out fast,
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
The message is rather more complicated than that. The later editions of Ralph Morrison's book do go into that in more detail than
the earlier editions.
--
Bill Sloman, Sydney
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vpm0qm$29gbe$1@dont-email.me...
On 26/02/2025 4:39 am, Christopher Howard wrote:
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduceGoogle for coaxial feed through capacitors.
ringing. but enough resistance can make the resonant circuit
critically damped and the voltages and current will decay
monotonically.
So, when you use a coaxial feed through capacitors on your Faraday cage, >>> do you add a resistor right after the capacitor, to reduce/eliminate
ringing?
The whole point about coaxial connectors is that the distributed capacitance and inductance gives you a R50R transmission line.
The only way to get "ringing" out of that is to fail to terminate the transmission line with it's characteristic impedance. In
practice it is hard to do it perfectly and you do tend to get low level reflections, but they die out fast,
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
The message is rather more complicated than that. The later editions of Ralph Morrison's book do go into that in more detail than
the earlier editions.
The sixth edition only mentions the "feed-through" capacitor in one paragraph on page 65.
The fifth edition does not mention them at all as far as I can tell.
On 26/02/2025 4:55 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message
news:vpm0qm$29gbe$1@dont-email.me... > On 26/02/2025 4:39 am, Christopher >Howard wrote: >> Bill Sloman <bill.sloman@ieee.org> writes: >>
On 25/02/2025 4:46 am, Christopher Howard wrote: >> Google for >>>>coaxial feed through capacitors. Capacitors and resistors don't ring. >>>>Adding inductance can introduce ringing. but enough resistance can >>>>make the resonant circuit critically damped and the voltages and >>>>current will decay monotonically.
So, when you use a coaxial feed through capacitors on your Faraday
cage, do you add a resistor right after the capacitor, to
reduce/eliminate ringing?
The whole point about coaxial connectors is that the distributed
capacitance and inductance gives you a R50R transmission line. The only
way to get "ringing" out of that is to fail to terminate the
transmission line with it's characteristic impedance. In practice it
is hard to do it perfectly and you do tend to get low level
reflections, but they die out fast,
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
The message is rather more complicated than that. The later editions of
Ralph Morrison's book do go into that in more detail than the earlier
editions.
The sixth edition only mentions the "feed-through" capacitor in one
The paragraph on page 65. fifth edition does not mention them at all as
The far as I can tell.
Feed-through capacitors seem only to be used in RF electronics, and
Ralph Morrison's book initially concentrated on regular industrial electronics.
Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2025 4:55 pm, Edward Rawde wrote:
The sixth edition only mentions the "feed-through" capacitor in one
The paragraph on page 65. fifth edition does not mention them at all as
The far as I can tell.
Feed-through capacitors seem only to be used in RF electronics, and
Ralph Morrison's book initially concentrated on regular industrial
electronics.
Industrial electronics may not contain RF devices but they are more and
more likely to be exposed to strong RF fields from external sources such
as mobile 'phones. Putting critical circuits inside metal boxes with
filters on the incoming wires is much more prevalent now than it was a
few years ago - the circuits haven't changed but the hostile environment
has.
On 26/02/2025 4:55 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vpm0qm$29gbe$1@dont-email.me...
On 26/02/2025 4:39 am, Christopher Howard wrote:
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Capacitors and resistors don't ring. Adding inductance can introduce >>>>> ringing. but enough resistance can make the resonant circuitGoogle for coaxial feed through capacitors.
critically damped and the voltages and current will decay
monotonically.
So, when you use a coaxial feed through capacitors on your Faraday cage, >>>> do you add a resistor right after the capacitor, to reduce/eliminate
ringing?
The whole point about coaxial connectors is that the distributed capacitance and inductance gives you a R50R transmission line.
The only way to get "ringing" out of that is to fail to terminate the transmission line with it's characteristic impedance. In
practice it is hard to do it perfectly and you do tend to get low level reflections, but they die out fast,
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
The message is rather more complicated than that. The later editions of Ralph Morrison's book do go into that in more detail
than
the earlier editions.
The sixth edition only mentions the "feed-through" capacitor in one paragraph on page 65.
The fifth edition does not mention them at all as far as I can tell.
Feed-through capacitors seem only to be used in RF electronics,
and Ralph Morrison's book initially concentrated on regular industrial electronics. Later editions did move on to higher frequency
applications.
I never used a feed-though capacitor anywhere in the work I did - if we need to put a fast signal through a conducting bulk-head
we used coax feed-throughs.
Feedthrough capacitors are relatively exotic devices.
Your example of their application seems to be a case where an RF specialist went in for a bit of over-kill.
--
Bill Sloman, Sydney
Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2025 4:55 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message
news:vpm0qm$29gbe$1@dont-email.me... > On 26/02/2025 4:39 am, Christopher >> >Howard wrote: >> Bill Sloman <bill.sloman@ieee.org> writes: >>
On 25/02/2025 4:46 am, Christopher Howard wrote: >> Google for
coaxial feed through capacitors. Capacitors and resistors don't ring.
Adding inductance can introduce ringing. but enough resistance can
make the resonant circuit critically damped and the voltages and
current will decay monotonically.
So, when you use a coaxial feed through capacitors on your Faraday
cage, do you add a resistor right after the capacitor, to
reduce/eliminate ringing?
The whole point about coaxial connectors is that the distributed
capacitance and inductance gives you a R50R transmission line. The only >> >> way to get "ringing" out of that is to fail to terminate the
transmission line with it's characteristic impedance. In practice it
is hard to do it perfectly and you do tend to get low level
reflections, but they die out fast,
Or are you just trying that all your inputs on the board have
resistors before whatever op amps or other components that they feed
into?
The message is rather more complicated than that. The later editions of >> >> Ralph Morrison's book do go into that in more detail than the earlier
editions.
The sixth edition only mentions the "feed-through" capacitor in one
The paragraph on page 65. fifth edition does not mention them at all as
The far as I can tell.
Feed-through capacitors seem only to be used in RF electronics, and
Ralph Morrison's book initially concentrated on regular industrial
electronics.
Industrial electronics may not contain RF devices but they are more and
more likely to be exposed to strong RF fields from external sources such
as mobile 'phones. Putting critical circuits inside metal boxes with
filters on the incoming wires is much more prevalent now than it was a
few years ago - the circuits haven't changed but the hostile environment
has.
Relays and cam timers may be set to make a comeback.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vpmnih$2gl7g$1@dont-email.me...
On 26/02/2025 4:55 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vpm0qm$29gbe$1@dont-email.me...
On 26/02/2025 4:39 am, Christopher Howard wrote:
Bill Sloman <bill.sloman@ieee.org> writes:
On 25/02/2025 4:46 am, Christopher Howard wrote:
Your example of their application seems to be a case where an RF specialist went in for a bit of over-kill.
Actually this is just a case of you making yet another completely wrong assumption.
Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.
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