Common Mode Noise

[Phil - NY4Q]

In an e-Conversation with Bas on the elimination of noise and offering a better receiver for the public, I came across this video which demonstrates the use of ferrite to work toward eliminating common-mode noise, so I wanted to share that to the group.

https://www.youtube.com/watch?v=b0Jx-oN3YlA

Now W1VLF is listening below 500kHz, so choose your ferrite mix accordingly when applying this to your setup.

Phil

[Bas ON5HB]

Hi Phil,

Very good find, as 1 movie shows better what it does then explanation in text.

BTW, it's not only working on VLF, but all bands including VHF/UHF/SHF etc, however, the higher the frequency the more unlikely common-mode will be a problem or noticed.

Therefor many newcomers to HF are blown out of the water when all of a sudden their shack is dancing on the transmission, speakers pop, lights turn on/off etc

We never had this on 70cm so HF is broken

[Martin G8JNJ]

Some good common sense information.

Steve G3TXQ (SK) did some good work on the design of common mode chokes and how to optimise them for specific frequencies. His simple chart is a useful reference for anyone wishing to reduce the level of common mode noise.

http://www.karinya.net/g3txq/chokes/

Differential and common mode noise from DC power supplies is also an issue, and adding a cheap DC filter board can often resolve a lot of issues too.

The main problem that I have observed tends to be common mode noise, where the power supply introduces an additional RF path to mains wiring and ground, and this noise ends up being conducted into the receive path.

Noise on the DC output is an issue, but this can usually be fixed by means of an external DC filter board. It will also help with common mode noise too.

The DC filter boards with two filter inductors and two electrolytics, as sold on sites such as AliExpress are the most suitable for use with Bias Tee's. Choose the type with the larger inductors.

https://www.aliexpress.com/w/wholesale-DC-Power-Filter-Board-0%2525252d50V-2A%252F3A%252F4A-Class-D-Power.html?spm=a2g0o.detail.search.0

Warning, resolving noise issues is like peeling the many layers of an onion, as soon as you fix one source, you often find another that was hidden underneath the previous layer. It can be an addictive pastime, and consume several kg of ferrite (& $$$) in the process.

Regards,

Martin