Radio with the "antenna" coiled around the mains!

[ivan747]

Hi! Taking apart a radio clock to change the headphone plug I noticed a wire coiled around tue mains wiring. Following it got me into a PCB pad called "Ant", near a very nastyly constructed FM radio module. Isn't this extremely dangerous? Will this affect the radio with mains hum?

I attached some photos.

Cheers,
Ivan

[Zero999]

It's certainly not a good idea for good reception but I don't see how it's a safety or hum problem.

FM radio frequencies are 2 million times as high as mains so no mains hum should get through the RF filter and the mains lead is double insulated so it's not a shock risk.

[kaptain_zero]

I suspect they decided to pick up FM freq. transmissions using an inductive pickup around the mains wiring with the mains acting as the antenna. There should be a separate AM ferrite rod antenna if it is AM/FM. The FM portion would not be affected by the 50/60hz hum entering the antenna hookup... the AM portion WOULD. I am also assuming that the mains wiring and the inductive loop are both insulated where they are next to each other so it would seem to be typical of this type of device.

Regards

Christian

[ivan747]

AM picks up lots of hum. I knew it was mains, but didn't knew the antenna was literally coiled around mains wiring. Ah well, who listens to AM these days anyway...

[Zero999]

Actually the mains hum on the AM is caused mainly by harmonics of the mains frequency rather than 50 or 60Hz itself. The FM band is far too high up to be affected by even the highest harmonics.