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I recently did a bit more research into the various DC filter boards that can be bough cheaply from China.

I've previously mentioned the simple type with two separate inductors.

Simple DC Filter

But I wanted to compare it against some of the larger types with an additional common mode choke using a dual winding. All of these seem to use the same printed circuit board, but populated with different types of inductors.

Green rectangular core common mode choke, and black core inductors

With toroidal common mode choke and yellow / white core inductors (Type 26 Iron Powder)

Differential Mode attenuation - direct noise from the power rails

All the filters are pretty effective. The simple type is slightly worse, but I doubt you would notice much difference between them in "real life"

Common mode attenuation - conducted noise, usually via a ground path

The Green and White cored filters are much more effective. The White cored filter would be slightly better at reducing low frequency <1MHz switching noise from Switched Mode Power Supplies, but the Green cored version provides much better overall attenuation.

Note that the values of attenuation were measured in a 50 ohm system, and the actual amount of attenuation will depend on the circuit impedance. However, using 50 ohms does at least provide a standard reference for comparison purposes.

Regards,

Martin

It's not that easy, as it depends on the source, and whatever it is connected to.

Especially as John has already indicated that there is likely to be more than one source.

That's why I suggest switching off your power at the main board, you will then be able to see what is under your control, and what is external.

Bringing the power back up, breaker by breaker, should allow you to better narrow down the location of a noise source.

Concentrate on one specific signal at a time, some of them will appear on many other frequencies.

Get rid of the worst offender first, and then gradually work on the others.

Be as methodical as possible.

Regards,

Martin

Most likely you will, so good hunting.

Oh and folks will soon be turning on their cheap Chinese made Christmas lights and decorations, so expect things to get worse for a month or so, until they get packed away again ready for next year.

Regards,

Martin

Oh I quite like that idea.

Maybe it could be linked to the user defined memories in some way too, and then perhaps a scan function could be added, with either timed or squelch controlled pause / resume.

However, I think John has more than enough to deal with at the moment, so I'd just leave it in the "possibly nice to have" future enhancement category / pile.

Regards,

Martin

Ah OK, like temporary user specific DX labels or were you something else ?

Regards,

Martin