Posted by R. Ticle on
URL: https://www.es-forum.com/Determining-AM-Radio-RF-frequencies-tp1549596.html

Hi everyone,

I've mentioned how I'd like to lower emissions on the Ethernet cable; I've now found that a lot of the noise from the cable is simply coming from being plugged into the computer, which is of course converting AC-DC, and the RF from the switch-mode conversion is being transferred along the Ethernet cable; also, the router and modem use AC-DC switching converters, which add to it; I hope to soon have a DC powered computer, and power the router/modem with a battery, to eliminate a lot of this RF.

However, there is still distinct noise coming from the modem itself. I clearly hear it with an AM radio, and I know what it is because it correlates with the "Data" light on the modem blinking. It is very easy to recognize the sound (I now even find it being picked up a bit by our corded telephone!)

Is there a way to determine the frequency of this data-transmission?

On the radio I can pick it up at either side of the scale, so it registers at 535 kilohertz and also 1,700 kilohertz.

What does that tell me?

I'm looking at using ferrite clamps and isolation from other cables as wellas better shielded cable to fix the problem...but what frequency-specific ferrite should I look for?

Cheers for any advice!

R.