[RFI] Noise changes when room lights turn on / off

[Eddy Swynar]

Hi Jim,

In answer to your first query re. my use of the word "incredibly", well, to ME at least, it truly was: we'd all spent the better part of the evening attempting to solve this neighbour's telephone RFI, and I was absolutely aghast when I couldn't hear a thing whilst seated beside the phone, yet she claimed that she could, standing beside me!

I really & truly thought that that either (A) she was a certifiable nut case, or that, (B) she revelled in all of the attention that she was getting, & was telling a fib! It was incredible to me because I never in my wildest dreams ever expected that the handset cord would act like a loaded antenna, fully extended like that. I imagine its natural resonance was somewhere in the 10-meter band, too!

And FWIW, the noise was NEVER totally eradicated when the cord was straightened like that---even with ferrite devices installed at both ends of it. It was "quiet" only when the cord was "bunched up"---straightened out, it acted like a perfect antenna.

~73~ de Eddy VDE3CUI - VE3XZ







On 2012-09-15, at 12:35 PM, Jim Brown wrote:

> On 9/15/2012 5:22 AM, Eddy Swynar wrote:
>> Incredibly, the coiled handset cord while I was seated was immune to RFI---but as soon as it was outstretched, it must have acted like a resonant loaded vertical on 10-meters!
> 
> Why do you use the word "incredibly" to describe simple antenna action?
> 
>> No amount of handset bypassing / filtering ever eliminated the RFI in the cord's uncoiled state
> 
> This might have succumbed to a couple of turns around a #43 or #31 ferrite core placed either on the cord to the handset, or to the telephone line cord.
> 
> FWIW, telephones are notoriously bad for RFI.
> 
> These RFI "war stories" are quite useful, including Pete's about those light switches.  There's clearly something about the construction of those switches that is allowing noisy leakage current when the switch is off, and interior house wiring is radiating it.
> 
> 73, Jim K9YC
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