Yup, that works well.
ps. The opposite applies as well.
The 5G vs plane altimeters concern, increase the BW and watch adjacent channels
raise the noise floor.
Are plane altimeters "grandfathered" because they didn't know about future
adjacent emitters ?
And so they did not design their receivers with sufficient selectivity ?
To be immune from a new player in the adjacent channels, even with a 200 MHz
margin ?
ps. does the new player comply with the required emissions limits ?
I suspect so ! And the receivers do not match the limits.
On Friday, May 6, 2022, 09:39:13 PM EDT, Brent DeWitt
<bdew...@ix.netcom.com> wrote:
Just to add a minor note to the thread:
The easiest way I use to determine if a signal is a "pure" clock harmonic, is
to simply punch down the RBW on the receiver/analyzer a bunch of times. If it
is a clock, you can reduce the RBW by a factor of as much as you have, and the
peak amplitude won't change.
Take care,
Brent DeWitt
On 5/6/2022 12:10 AM, Bill Owsley wrote:
If you set the step function to the 63 MHz freq, and then step up, BW set a
little wide to account for slight inaccuracy, do you find more emissions,
energy, harmonics, at the steps ?
If there is only the one peak, and it is a clean signal, suspect an curious
resonance.
Had one once, the trace was resonant and sang rather notably. A little
resistance at each end worked, but oddly, it took several guesses to find the
right value. ps. this was a clock trace that wrapped around 3.5 sides of
circuit board near the edge. Don't allow that to happen. Not fun,
interesting, but not fun.
The frequency rings a bell, but can't quite remember why.
Ethernet is 125 MHz, guess what half of that is near ?
If the observed signal is a solid shaped peak, I would first guess a clock of
a steady sort.
If a bit wobbly, modulated, a guess is that it has data on it, or might be
inter-modulation.
If a shape other than sine peak, wobbly or not, it might be frequency
modulated, usually called frequency hopping, and some actually are, which is a
mis-understanding in engineering.
pps. the spread sheet for clock harmonics is a good tool. We had one long
ago, that did all the divisions and multiplications. Then an easy effort to
look it up.
But if the developers don't give you a complete list of clocks, xtals, or
computed and used only in a chip, The sheet will help you tell them what their
chips are doing.
pps, that can get a bit embarrassing, since the designers don't know what
their chips are doing and they are building this to work. A 6 month delay,
been there, might happen before the secrets are revealed.
On Thursday, May 5, 2022, 10:08:14 AM EDT, Ken Wyatt
<k...@emc-seminars.com> wrote:
I was just going to suggest what James already did.
You should be able to take a small-diameter H-field probe and zero in on the
source. That may help.
If you email me directly, I’ll provide you a clock harmonic analyzer
spreadsheet developed by my co-author, Patrick André.
Cheers, Ken
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On May 5, 2022, at 3:16 AM, James Pawson (U3C) <ja...@unit3compliance.co.uk>
wrote:
Hi Amund, Narrowband or broadband noise? If broadband and you zoom in
to the noise on the analyser, is it made up of separate peaks? What is the
spacing between the peaks? Try using a near field probe to zoom in on the
emissions -
https://www.unit3compliance.co.uk/graphical-guide-to-emc-near-field-probing/
All the best James James Pawson Managing Director & EMC Problem Solver
Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE
& UKCA : Consultancy www.unit3compliance.co.uk |
ja...@unit3compliance.co.uk +44(0)1274 911747 | +44(0)7811 139957 2
Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and
Wales # 10574298 From: Amund Westin <am...@westin-emission.no>
Sent: 05 May 2022 09:50
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Chasing a specific frequency During a radiated emission
test, we have a problem with one specific frequency, 63MHz. Not exactly
63.00MHz but like 63.03406…. We have calculated all combinations of
intermodulation products from oscillators on the pcb, but no one match the
63MHz. There are a lots of DC/DC converters on the board, and I suspect low
switching frequencies (≈1MHz) may be the source and problem. How this low
frequency signal became 63MHz noise, it must be (could be … or?) a combination
of harmonics and layout circuitry that optimize unwanted antenna performance
and then result in a powerful noise component at 63MHz. At this stage, we have
not investigated the trace layouts or the layers stacking of the pcb. We have
done some introduction of clean power (batteries) and in the same time,
bypassed DCDC converters to observe the difference in noise spectrum. On the
right track? BR
Amund -
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