UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - How effective is an earth for reducing noise on AM?

G6Tanuki · 25th Nov 2020, 5:52 pm

I guess 'how effective is an earth at removing noise' depends on _how_ the noise is getting into the receiver; if it's mains-borne then just adding another earth [your DNO's grounding-schema also being relative for safety reasons] won't necessarily make much difference.

With my Eddystone 840A bedside radio the thing I did find made ab improvement was fitting a common-mode choke to the [2-core] mains cable _and_ using an earth. The common-mode choke stops noise coming via the mains; if you just add an earth without 'choking' the supply then noise on the mains may actually flow through the earth-impedance of your new earth and possibly make noise worse!

[My common-mode choke is a small ferrite item scavenged from a switched-mode computer power-supply, mounted in a diecast box and installed about 10 feet from the radio]

25th Nov 2020, 5:52 pm	#26
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: How effective is an earth for reducing noise on AM? I guess 'how effective is an earth at removing noise' depends on _how_ the noise is getting into the receiver; if it's mains-borne then just adding another earth [your DNO's grounding-schema also being relative for safety reasons] won't necessarily make much difference. With my Eddystone 840A bedside radio the thing I did find made ab improvement was fitting a common-mode choke to the [2-core] mains cable _and_ using an earth. The common-mode choke stops noise coming via the mains; if you just add an earth without 'choking' the supply then noise on the mains may actually flow through the earth-impedance of your new earth and possibly make noise worse! [My common-mode choke is a small ferrite item scavenged from a switched-mode computer power-supply, mounted in a diecast box and installed about 10 feet from the radio]