AM radio reception: interference noise problem

[eblc1388]

I tried to help out an old age friend of mine to tackle an AM radio reception problem. It is a simple portable transistorize radio.

He lives in a multi-stories building and recently the reception of his favorite AM radio stations were hampered by a lot of switching noises and interference, like those coming from switching power supplies and CFL lights.

I tried moving the radio to another room with good success and the reception is fine in that location. So I think it would be a piece of cake just to reconnect the speaker output back to his present location of the room.

However, the moment I connect an external speaker and a 30 feet extension cable into the radio via the ear phone jack, the interference comes back and I am back to square one. Obviously the long cable also acts as an effective antenna.

Any suggestions on what I can do to stop the speaker cable acting as an antenna?

 

[Mikebits]

Maybe wrap the cable--where it feeds into the radio--around a ferrite bead. One of those big ones.

 

[Dean Huster]

Or bypass both speaker/headphone lines with a 0.01µF disc cap to ground.

I was listening to my local AM station while I was building a 30 x 40' shop for a guy. I installed three banks of florescent lights (that's 24 8-foot tubes!), switched them on and had to switch the radio over to FM.

If you think traditional AM reception is a problem these days, you should try out HF shortwave. CFLs, switching power supplies (in anything that has a remote it seems) computers and their monitors whether on or off, light dimmers, ceiling fan speed controls, neighbors with arc welders .... the list goes on and on.

Dean

 

[erosennin]

Yes!! The crap I have to deal with to get decent shortwave reception pisses me off... Although I do this mostly at night, when most of these appliances are switched off, there is a lot of surrounding rubbish that interferes and causes me angst.

By the way, if the monitor is off, it will still cause interference, but I've found if you unplug it from the computer i.e. the VGA or DVI cable, this helps a great deal.

Also, MW reception is also a problem for me as that's what I listen to mostly. I'm thinking it's a power supply issue so I'm going to try and make an isolation circuit of some description and see if it helps... And maybe try one of those "Active" antennas, or some other kind of antenna, I'm not allowed to put up a big antenna outside...

 

[mvs sarma]

We may perhaps remove the internal antenna( with ferrite rod) and try adopting a M/W loop antenna . The loop ant may have to be placed on roof top with remote control for orientation and tuning. The output may be brought down to user through a Coaxial cable.
With his arrangement most of the noise can be reduced.

this links to a model as sold in UK
Active Loop Antenna ALA330S reduces local interference on shortwave, medium wave, long wave

 

[eblc1388]

Thanks.

I'll try the suggestion of a few turns on a ferrite ring, along with the capacitors to ground.

Would the normal AC power input EMI filter block(those with common mode choke and capacitors inside a metal can) any good for this situation?

 

[Mikebits]

Yes!! The crap I have to deal with to get decent shortwave reception pisses me off... Although I do this mostly at night.

One reason night time works better is less solar interaction, believe it or not...
Solar activity really mucks up a SW radio.

 

[erosennin]

Yeah I know that bit of information, which I why I constrain my listening to the night time hours, 9pm to 3-4am...
But the other garbage that Dean suggested is what bothers me.

 

[Mikebits]

Yeah I know that bit of information, which I why I constrain my listening to the night time hours, 9pm to 3-4am...
But the other garbage that Dean suggested is what bothers me.

I would think it would be more fun to chase dingos. lol, just kidding. Yeah you can't escape the ever increasing radio noise pollution that no one can hear but the SW listener. I use to work for a HAM radio company called SWAN, ever heard of it? Back in the day SWAN was a cool rig.

 

[Mikebits]

Thanks.

I'll try the suggestion of a few turns on a ferrite ring, along with the capacitors to ground.

Would the normal AC power input EMI filter block(those with common mode choke and capacitors inside a metal can) any good for this situation?

You know, I firmly believe that solving EMI problems is an art, and not science. I am often amazed at what solves an interference problem. My suggestion is try everything that people have suggested, and hope something works.
I once installed a stereo system in Bill Waltons motor home--former NBA celtic--and the stereo whined and sounded like crap. I tried everything to fix it. Solutions was a DC converter, nothing else worked.
Moral of the story, just try junk until the junk is gone

 

[erosennin]

Hahaha, sometimes, I'd rather be doing that too. Lately I've left any listening to the uni breaks when I don't have to wake up early the next day...

No sorry, I can't say I have...
I use a Sangean though...

 

[Mikebits]

How far have you transmitted? Thats the thing for a SW person I think. It is really cool to send your voice across an ocean is it not?
When satellites fail SW will still be the linking force

 

[erosennin]

Hahaha, no sorry, no Xmitt for me... I just listen to what everyone else is transmitting...
I use the internet for that... =p

 

[Hero999]

The capacitor, ferrite bead and EMI filter are all good ideas but have you considered using screened cable to feed the speaker?

 

[Rajaneesh]

I tried to help out an old age friend of mine to tackle an AM radio reception problem. It is a simple portable transistorize radio.

He lives in a multi-stories building and recently the reception of his favorite AM radio stations were hampered by a lot of switching noises and interference, like those coming from switching power supplies and CFL lights.

I tried moving the radio to another room with good success and the reception is fine in that location. So I think it would be a piece of cake just to reconnect the speaker output back to his present location of the room.

However, the moment I connect an external speaker and a 30 feet extension cable into the radio via the ear phone jack, the interference comes back and I am back to square one. Obviously the long cable also acts as an effective antenna.

Any suggestions on what I can do to stop the speaker cable acting as an antenna?

Instead of doing all this research, use a shielded cable from the phone jack to the speaker and ground the shield to the supply ground.

Hope this will help...

 

[Bob Scott]

Ground the radio to an electrical socket ground. If the radio does not have a ground terminal, wire the negative battery terminal to an electrical socket ground. This will have a PROFOUND effect on eliminating AM noise.

 

[eblc1388]

Thanks all for your suggestions. The interference problem when an external speaker is connected to an AM radio has been rectified using the following:

A 1:1 isolation transformer for the speaker signal. A grounding is applied to one core of the 30 feet non-shielded speaker cable and a ferric bead/ring with a few turns of both the DC power supply feed and the speaker feed before connecting to the portable radio.

So for DC to radio, a few turns through ferric bead then to radio. For audio from radio, a few turns via same ferric bead, then to isolating transformer and finally to the earthed 30 feet speaker cable.

Hope it would be of some help to someone else.