Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
On Wednesday, November 9, 2022 at 11:17:04 PM UTC-4, John Larkin wrote:
On Thu, 10 Nov 2022 02:45:40 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:
Clifford Heath <no_...@please.net> wrote:
On 10/11/22 10:47, John Larkin wrote:
\"Avoid ground loops\" makes no sense for fast stuff, and doesn\'t even
make sense for audio or thermocouples.
Says the man who\'s obviously never operated an audio system in a hall
where you can get >1VAC between the grounds of different outlets.
Don\'t they make transformers for that situation?
Of course, nowadays everything is probably WiFi. Look at the stage
microphones used by Taylor Swift, Madonna, Rihanna and others.
RF doesn\'t have ground loops! Fiber doesn\'t either.
No, but shields connected at both ends along with other ground connections do.
On Thursday, November 3, 2022 at 10:37:53 AM UTC-4, Joe Gwinn wrote:
On Wed, 02 Nov 2022 20:00:00 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
So, how wide and how fast should I sweep?
Wobbling the clock frequency to reduce EMI is in fact a standard
trick going back decades, with commodity chips to do just that.
.<https://www.eetimes.com/isscc-spread-spectrum-clocks-mitigate-emi/
I\'ve always wondered if frequency wobbling is a method to reduce the
interference impact of the emissions, or if it is just a way to
impact the measurement. The same amount of power is being emitted at
a given bandwidth at the time the sweep passes that range, swept or
not. I would image there are victim devices that would still be
impacted in the same way, even with the frequency sweeping.
On 09/11/2022 16:42, Ricky wrote:
On Thursday, November 3, 2022 at 10:37:53 AM UTC-4, Joe Gwinn wrote:
On Wed, 02 Nov 2022 20:00:00 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
So, how wide and how fast should I sweep?
Wobbling the clock frequency to reduce EMI is in fact a standard
trick going back decades, with commodity chips to do just that.
.<https://www.eetimes.com/isscc-spread-spectrum-clocks-mitigate-emi/
I\'ve always wondered if frequency wobbling is a method to reduce the
interference impact of the emissions, or if it is just a way to
impact the measurement. The same amount of power is being emitted at
a given bandwidth at the time the sweep passes that range, swept or
not. I would image there are victim devices that would still be
impacted in the same way, even with the frequency sweeping.
It is a bit of both. If the radiated power at f0 is reduced by spreading
it out a bit you might hit other resonances.
But a spectrum analyser is the worst case seeing all of it.
A 10 fold reduction at any single frequency might still be good enough
to pass even if more frequencies are now affected by its influence.
Conservation of energy says that it has to go somewhere.
On Thursday, 10 November 2022 at 06:24:21 UTC, Ricky wrote:
On Wednesday, November 9, 2022 at 11:17:04 PM UTC-4, John Larkin wrote:
On Thu, 10 Nov 2022 02:45:40 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:
Clifford Heath <no_...@please.net> wrote:
On 10/11/22 10:47, John Larkin wrote:
\"Avoid ground loops\" makes no sense for fast stuff, and doesn\'t even
make sense for audio or thermocouples.
Says the man who\'s obviously never operated an audio system in a hall
where you can get >1VAC between the grounds of different outlets.
Don\'t they make transformers for that situation?
Of course, nowadays everything is probably WiFi. Look at the stage
microphones used by Taylor Swift, Madonna, Rihanna and others.
RF doesn\'t have ground loops! Fiber doesn\'t either.
No, but shields connected at both ends along with other ground connections do.
Which is why a suitable series capacitor in one end of the grounded shield
can be a good idea. It blocks 50/60Hz but is almost a short circuit at RF..
On Thursday, November 10, 2022 at 5:55:47 AM UTC-4, John Walliker wrote:
On Thursday, 10 November 2022 at 06:24:21 UTC, Ricky wrote:
On Wednesday, November 9, 2022 at 11:17:04 PM UTC-4, John Larkin wrote:
On Thu, 10 Nov 2022 02:45:40 -0000 (UTC), Mike Monett VE3BTI
spa...@not.com> wrote:
Clifford Heath <no_...@please.net> wrote:
On 10/11/22 10:47, John Larkin wrote:
\"Avoid ground loops\" makes no sense for fast stuff, and doesn\'t even
make sense for audio or thermocouples.
Says the man who\'s obviously never operated an audio system in a hall
where you can get >1VAC between the grounds of different outlets..
Don\'t they make transformers for that situation?
Of course, nowadays everything is probably WiFi. Look at the stage
microphones used by Taylor Swift, Madonna, Rihanna and others.
RF doesn\'t have ground loops! Fiber doesn\'t either.
No, but shields connected at both ends along with other ground connections do.
Which is why a suitable series capacitor in one end of the grounded shield
can be a good idea. It blocks 50/60Hz but is almost a short circuit at RF.
What is the advantage of using the cap? If there is a good ground between the systems, are you suggesting it\'s not an RF ground? Anyway, for a shield connected to a connector shell, grounding through a cap is an awkward thing to do. They are designed to provide a ground through mounting. Where exactly does the cap go? The cable itself?
I would think any RF design is going to pay attention to details, rather than using a cookbook approach.
On Thursday, 10 November 2022 at 06:24:21 UTC, Ricky wrote:
On Wednesday, November 9, 2022 at 11:17:04 PM UTC-4, John Larkin wrote:
RF doesn\'t have ground loops! Fiber doesn\'t either.
No, but shields connected at both ends along with other ground connections do.
Which is why a suitable series capacitor in one end of the grounded shield
can be a good idea. It blocks 50/60Hz but is almost a short circuit at RF.
On Thursday, 10 November 2022 at 11:02:55 UTC, Martin Brown wrote:
On 09/11/2022 16:42, Ricky wrote:
On Thursday, November 3, 2022 at 10:37:53 AM UTC-4, Joe Gwinn wrote:
On Wed, 02 Nov 2022 20:00:00 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
So, how wide and how fast should I sweep?
Wobbling the clock frequency to reduce EMI is in fact a standard
trick going back decades, with commodity chips to do just that.
.<https://www.eetimes.com/isscc-spread-spectrum-clocks-mitigate-emi/
I\'ve always wondered if frequency wobbling is a method to reduce the
interference impact of the emissions, or if it is just a way to
impact the measurement. The same amount of power is being emitted at
a given bandwidth at the time the sweep passes that range, swept or
not. I would image there are victim devices that would still be
impacted in the same way, even with the frequency sweeping.
It is a bit of both. If the radiated power at f0 is reduced by spreading
it out a bit you might hit other resonances.
But a spectrum analyser is the worst case seeing all of it.
A 10 fold reduction at any single frequency might still be good enough
to pass even if more frequencies are now affected by its influence.
Conservation of energy says that it has to go somewhere.
A 10-fold reduction isn\'t enough. JL needs to reduce the level by 30dB.
The bandwidth of the EMC measurement receiver will almost certainly be
120kHz, so the frequency modulation would need to be extreme to achieve
that by FM alone. The quasi-peak detector has an attack time of 1ms
and a decay time of 550ms.
With a uniform frequency sweep of +/-50% I estimate that the measurement will
drop by about 27dB which is not enough.
John
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
On 2022-11-03, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
30-33kHz modulation frequency seem to be standard. There are lots of
ready-made SSC clock generators, and even 5*7mm-style crystal oscillators
with SSC output.
For CPU clocks etc., I like the SI5351A clock generator (if you can get them
since Skyworks bought the parts). You can either order them pre-programmed,
or you can set the registers via I2C after each power-on (that even works on
pre-programmed parts). PLLA can do SSC with configurable parameters, and
125MHz is in the range of supported outputs.
cu
Michael
On 9 Nov 2022 10:32:55 GMT, Michael Schwingen
news-15...@discworld.dascon.de> wrote:
On 2022-11-03, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
30-33kHz modulation frequency seem to be standard. There are lots of
ready-made SSC clock generators, and even 5*7mm-style crystal oscillators
with SSC output.
That\'s interesting. We could just drop one into our board. Cool.
We do have a PLL inside our FPGA that multiplies the 125 MHz clock up,
to clock a 250 MHz ADC. A little jitter wouldn\'t bother me (the signal
is grossly oversampled) but we need the PLL to still work.
For CPU clocks etc., I like the SI5351A clock generator (if you can get them
since Skyworks bought the parts). You can either order them pre-programmed,
or you can set the registers via I2C after each power-on (that even works on
pre-programmed parts). PLLA can do SSC with configurable parameters, and
125MHz is in the range of supported outputs.
cu
Michael
Great. Thanks.
On Wed, 02 Nov 2022 20:00:00 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
We make a bunch of boxes that go into a semi fab tool. One measures an
optical waveform and shoots it to a bigger box, over three twisted
pairs (clock, data, data) using shielded RJ45 ethernet type stuff.
When we originally did it, they told us we were exempt from ROHS and
EMI standards, but now we aren\'t. ROHS is no big deal, but the little
box makes a continuous 62 MHz clock, differential at 5 volt swings,
and radiates too much.
We can\'t lowpass filter the fundamental of course. We can\'t drop the
amplitude much. A common-mode balun might help some.
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
My options are to add a modulated phase shifter in the clock path, or
to replace the main XO with a VCO and apply some waveform to the VCO
input to FM the whole FPGA clock and everything. Clock and data would
sweep together, which is kind of nice.
So, how wide and how fast should I sweep?
Wobbling the clock frequency to reduce EMI is in fact a standard trick
going back decades, with commodity chips to do just that.
.<https://www.eetimes.com/isscc-spread-spectrum-clocks-mitigate-emi/
On Wednesday, 9 November 2022 at 14:39:38 UTC, John Larkin wrote:
On 9 Nov 2022 10:32:55 GMT, Michael Schwingen
news-15...@discworld.dascon.de> wrote:
On 2022-11-03, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
30-33kHz modulation frequency seem to be standard. There are lots of
ready-made SSC clock generators, and even 5*7mm-style crystal oscillators
with SSC output.
That\'s interesting. We could just drop one into our board. Cool.
We do have a PLL inside our FPGA that multiplies the 125 MHz clock up,
to clock a 250 MHz ADC. A little jitter wouldn\'t bother me (the signal
is grossly oversampled) but we need the PLL to still work.
For CPU clocks etc., I like the SI5351A clock generator (if you can get them
since Skyworks bought the parts). You can either order them pre-programmed,
or you can set the registers via I2C after each power-on (that even works on
pre-programmed parts). PLLA can do SSC with configurable parameters, and
125MHz is in the range of supported outputs.
cu
Michael
Great. Thanks.
Why not convert the clock into a pseudo-random sequence and XOR that with the
data. That way, both the clock and data will have a white noise spectrum (shaped
with a sinc that has a zero at the clock frequency). Reverse the process at the
other end.
As you are using fpgas the extra overhead should be minimal.
Alternatively, you could use Manchester coding which would achieve a similar result.
John
On Wed, 9 Nov 2022 07:35:53 -0800 (PST), John Walliker
jrwal...@gmail.com> wrote:
On Wednesday, 9 November 2022 at 14:39:38 UTC, John Larkin wrote:
On 9 Nov 2022 10:32:55 GMT, Michael Schwingen
news-15...@discworld.dascon.de> wrote:
On 2022-11-03, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
So one idea is to spread-spectrum, wobulate the clock frequency or
phase to smear the spectral peak below the CE limits.
Has anyone done this? I wonder how wide a frequency sweep we\'d need
but more important is what the equivalent FM modulation frequency
would have to be so the spectrum analyzer never sees the peak spectral
line. Imagine a sawtooth frequency modulation, which turns the
spectral spike into a nice flat plateau. What sort of sawtooth
frequency would work?
30-33kHz modulation frequency seem to be standard. There are lots of
ready-made SSC clock generators, and even 5*7mm-style crystal oscillators
with SSC output.
That\'s interesting. We could just drop one into our board. Cool.
We do have a PLL inside our FPGA that multiplies the 125 MHz clock up,
to clock a 250 MHz ADC. A little jitter wouldn\'t bother me (the signal
is grossly oversampled) but we need the PLL to still work.
For CPU clocks etc., I like the SI5351A clock generator (if you can get them
since Skyworks bought the parts). You can either order them pre-programmed,
or you can set the registers via I2C after each power-on (that even works on
pre-programmed parts). PLLA can do SSC with configurable parameters, and
125MHz is in the range of supported outputs.
cu
Michael
Great. Thanks.
Why not convert the clock into a pseudo-random sequence and XOR that with the
data. That way, both the clock and data will have a white noise spectrum (shaped
with a sinc that has a zero at the clock frequency). Reverse the process at the
other end.
As you are using fpgas the extra overhead should be minimal.
Alternatively, you could use Manchester coding which would achieve a similar result.
John
The customer has designed an elaborate controller (it took them a few
years) and doesn\'t want to change it, but is failing EMI. We would
prefer to not change our box much either, any time soon. It\'s an
interesting political situation.
If we could change things, we could go 8b10b on the data lanes and
have no clock pair in the cable. 8b10b is sort of spread-spectrum
already, and tricks can make it better.
We make a bunch of boxes that go into a semi fab tool. One measures an
optical waveform and shoots it to a bigger box, over three twisted
pairs (clock, data, data) using shielded RJ45 ethernet type stuff.
We make a bunch of boxes that go into a semi fab tool. One measures an
optical waveform and shoots it to a bigger box, over three twisted
pairs (clock, data, data) using shielded RJ45 ethernet type stuff.
When we originally did it, they told us we were exempt from ROHS and
EMI standards, but now we aren\'t. ROHS is no big deal, but the little
box makes a continuous 62 MHz clock, differential at 5 volt swings,
and radiates too much.
We can\'t lowpass filter the fundamental of course. We can\'t drop the
amplitude much. A common-mode balun might help some.
On Thursday, November 3, 2022 at 10:37:53 AM UTC-4, Joe Gwinn wrote:
Wobbling the clock frequency to reduce EMI is in fact a standard trick
going back decades, with commodity chips to do just that.
.<https://www.eetimes.com/isscc-spread-spectrum-clocks-mitigate-emi/
I\'ve always wondered if frequency wobbling is a method to reduce the interference impact of the emissions, or if it is just a way to impact the measurement. The same amount of power is being emitted at a given bandwidth at the time the sweep passes that range, swept or not. I would image there are victim devices that would still be impacted in the same way, even with the frequency sweeping.
torsdag den 3. november 2022 kl. 04.00.11 UTC+1 skrev John Larkin:
We make a bunch of boxes that go into a semi fab tool. One measures an
optical waveform and shoots it to a bigger box, over three twisted
pairs (clock, data, data) using shielded RJ45 ethernet type stuff.
When we originally did it, they told us we were exempt from ROHS and
EMI standards, but now we aren\'t. ROHS is no big deal, but the little
box makes a continuous 62 MHz clock, differential at 5 volt swings,
and radiates too much.
We can\'t lowpass filter the fundamental of course. We can\'t drop the
amplitude much. A common-mode balun might help some.
if it is balanced why do you need such a massive swing?
On Wednesday, November 2, 2022 at 8:00:11 PM UTC-7, John Larkin wrote:
We make a bunch of boxes that go into a semi fab tool. One measures an
optical waveform and shoots it to a bigger box, over three twisted
pairs (clock, data, data) using shielded RJ45 ethernet type stuff.
Probably a dumb question, but those clock and data signals are source-
terminated to drive ~100 ohms, right? If you have standing waves
on the wire pairs, I can see them exciting the ungrounded shield at the
current points, making a very effective antenna. Radiation from the
cable could easily be 30 dB worse than expected.
-- john, KE5FX