Question about Oxley RFI suppression filters FLTM/P/5000

Sorry I don’t know the internal construction but suspect the inductor is possibly not a coil but merely the central conductor passing through a ferrite sleeve. In those feedthroughs the capacitors are often annular too so nothing is left to chance.

You haven’t said what the frequency is of the ripple that you observe, those devices will have negligible effect at powerline frequency.

Typically 5 to 20 MHz.

Ok, thanks. I’d expect they’d be very effective at VHF/UHF but should already be showing some insertion loss by 5MHz

EMI filters only filter high frequency stuff, AM band and up. If your problem is AC-line frequency ripple or low frequency switcher noise, a typical EMI filter won'[t help.

What does the contamination look/sound like?

This is well documented. Insersion loss = about 30 dB at 10 MHz and about 70 dB at 100 MHz. I checked it.

At 10 MHz the ripple of my power supplies contaminates my output signal at a level much higher than the documented inserson loss.

So I suspect some 10 MHz makes its way through a magnetic field and perhaps a filter with only a simple annular capacitor would be more effective.

It looks like your circuit has gain from power-in to output. That's bad.

Anyway, it's poor practice to expect a feedthrough filter to clean switcher noise off your power lines.

Jeroen Belleman

Common in single-ended circuits, though. I do a lot of discrete amps and (for my sins) photoreceivers, which use two-transistor, four-pole cap multipliers with >>100 dB rejection at SMPS frequencies.

Cheers

Phil Hobbs

HF noise coupling paths may not all be visible on the schematic. I could tell horror stories.

Some switchers are really nasty.

Jean-Pierre, what switcher are you using?