[RFI] Doorbell Transformer RFI ??

[Pete Smith N4ZR]

I've found it very persuasive with the neighbors to bring along a 
portable radio and let them hear the arc.  Then I say something like, 
"That'sa spark and it is somewhere in your house, maybe inside the walls 
or ceiling.  I don't need to tell you what can happen, do I?"

73, Pete N4ZR
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On 3/15/2016 12:32 AM, WX5L wrote:
> The older type doorbell transformer has a safety feature built in. A
> thermister monitors the heat in the windings. If it detects overheating it
> opens a relay to disconnect power so it doesn't combust.
> But even with a normal situation this relay can become pitted and chatter
> away causing RFI. An easy fix if it's yours but neighbors are often very
> skeptical of changing anything especially if it's not bothering them.
>
> Forced air attic ventilators thermostats can cause RFI as they age
> especially if they are near the fan as it vibrates the surrounding area.
>
> Randy
> WX5L
>
> -----Original Message-----
> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Jim Brown
> Sent: Monday, March 14, 2016 10:55 PM
> To: Rfi List
> Subject: [RFI] Doorbell Transformer RFI ??
>
> I've heard for years that doorbell transformers could be noisy, yet the
> mechanism was not clear and I've never found one that was noisy.
>
> But it just hit me -- electrical supply houses sell no-name, unlabeled
> switch-mode power supplies to provide low voltage DC for low voltage
> lighting circuits, and they CALL them "electronic transformers." Is it
> possible that the noisy doorbell transformers I've heard about are really an
> SMPS? Or is it a real transformer whose windings have deteriorated?
>
> 73, Jim K9YC
>
>
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