Are you sure this is not any EMI just took by the probe of the scope meter ? Try to make a simple test by short-circuiting both terminals of the probe of this chanel, connecting them to the same energized part of the SMPS (e.g the 12v itself) just to check if the problem persists, which would lead to the conclusion that could be just an issue related to the measurement process. Anyway, considering the narrowness of this artifact, I would not consider this as an issue at the load side in having ceramic capacitors close to the board entry.
if you are measuring ripple, then use a proper ripple probe, eg, a piece of coaxial cable.
Scope leads with dangling tail always show loads of pickup with any smps.
What you show on the scope trace looks like "pickup", that isnt due to the electrolytics being gone, (but i am not saying they are not gone, they might be a bit frazzled, idont know)
oh right, it just shows how much capacitive coupling there is of the smps noise into the chassis.....then the chassis is helping to re-radiate it.
Thanks for your reply, the picture shows a signal on 30 Mhz with spur at 50 Hz, it happenns also in any other frequencies, 10Ghz, 10hz, etc..., even without any signal on the 0 hz spectrum analyzer peak. but doing a larger span, it also shows the spurs with less amplitude also at 150hz, 350hz, etc... (not shown on the picture)30 MHz interferences (as shown in post #4) will be mostly conducted through cables rather than radiated. In so far shielding of the SMPS has limited effect, filtering the SMPS in- and outputs is the relevant method to reduce it. The dominance of conducted emissions is a simple matter of wavelength versus circuit size.
A SMPS with a switching frequency of some 10 to maximal 100 or 150 kHz won't emit a single 30 MHz line, but a complete "fence" of switching frequency harmonics. Some frequencies might be "amplified" by circuit resonances, but there are surely many interfering frequency. It would be informative to see the full picture instead of only one line with 50 Hz sidebands.
Hi,
Picutre says 30MHz = 30000000Hz
But you say 50Hz
Why there is that huge difference?
Klaus
O.K., suggests that the mains interference is coupled into the oscillator, IF amplifier or detector. There should be no radiated interference at 0 Hz, isn't it.
50 Hz side band suggests that it's not a dried-out filter capacitor (would give 100 Hz ripple) and even 50 Hz harmonics.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?