Author Topic: Radio with the "antenna" coiled around the mains!  (Read 2792 times)

0 Members and 1 Guest are viewing this topic.

Offline ivan747Topic starter

  • Super Contributor
  • ***
  • Posts: 2045
  • Country: us
Radio with the "antenna" coiled around the mains!
« on: June 18, 2011, 04:56:11 pm »
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
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 19516
  • Country: gb
  • 0999
Re: Radio with the "antenna" coiled around the mains!
« Reply #1 on: June 18, 2011, 05:07:21 pm »
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.
 

Offline kaptain_zero

  • Regular Contributor
  • *
  • Posts: 180
  • Country: ca
Re: Radio with the "antenna" coiled around the mains!
« Reply #2 on: June 18, 2011, 05:08:17 pm »
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
 

Offline ivan747Topic starter

  • Super Contributor
  • ***
  • Posts: 2045
  • Country: us
Re: Radio with the "antenna" coiled around the mains!
« Reply #3 on: June 18, 2011, 05:14:43 pm »
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...
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 19516
  • Country: gb
  • 0999
Re: Radio with the "antenna" coiled around the mains!
« Reply #4 on: June 18, 2011, 05:37:17 pm »
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.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf