radio feature in nokia phone

[TheVictim]

Since analog television is biting the dust in 2009, I wonder when we are going to see the AM broadcast band as we know it going bye-bye. I can see digitally coded SSB taking it over.

 

[bananasiong]

Is there an extra wire for the antenna in the earphone? Or the left and right side line act as antenna?

 

[mdanh2002]

Is there an extra wire for the antenna in the earphone? Or the left and right side line act as antenna?

I am wondering also. How can the left and the right side act as an antenna while audio signals are also travelling inside? and the earphone doesn't have extra wire for antenna, yet it is still being used as an external antenna!

 

[Hero999]

Since analog television is biting the dust in 2009, I wonder when we are going to see the AM broadcast band as we know it going bye-bye. I can see digitally coded SSB taking it over.

I would like to see that, however there is the issue of millions of radios been rendered obsolete.

At the moment, analogue radios are still cheaper to make thant digital radios but this might if digital takes over.

Then there's the fact that all those old radios rotting in landfill isn't very good for the environment.

 

[audioguru]

No additional wire is needed when the headphones wires are used as an antenna:

Choke coils in series with the headphones wires pass the audio signal but block the RF signal from being shorted by the audio amp's output.
Then the RF signal is coupled to the radio through a low value capacitor that has no effect on the audio signal.

 

[bananasiong]

No additional wire is needed when the headphones wires are used as an antenna:

Choke coils in series with the headphones wires pass the audio signal but block the RF signal from being shorted by the audio amp's output.
Then the RF signal is coupled to the radio through a low value capacitor that has no effect on the audio signal.

Wow, this is so interesting, I have never heard about this. So the earphone wire has to be long enough in order to receive the signal well? How if the wire is bent? I thought the single pole antenna has to be straight and the length of at least a quarter of the wavelength?

Thanks

 

[audioguru]

If the antenna wire is a quarter-wavelength long and is in the same plane as the transmitting antenna then the reception is best. If the antenna is shorter or is not pointing in the correct direction then the reception is reduced but it is not zero. If the signal strength is strong and the radio is very sensitive then the antenna doesn't make any difference.

 

[mdanh2002]

If the antenna wire is a quarter-wavelength long and is in the same plane as the transmitting antenna then the reception is best.

lambda = c / f, c=speed of light=3e8 m/s
Assuming 100MHz frequency for FM: lambda = 3e8 / 100e6 = 3 metres

"quarter-wavelength" --> preferred antenna length = 3 / 4 = 0.75m = 75cm

Is this the 80cm piece of wire I always heard in most FM transmitter forum threads?

 

[Hero999]

Yes.

This waste of space is because the crappy forum software won't allow me to make sort replies.

 

[TheVictim]

In laymans terms, the radio wave in reality is actually 1/4 the size of it's wavethength in physical dimensions. When a radio wave hits a receiver's antenna, it induces a very tiny current flow in the antenna. If the antenna isn't long enough, part of the wave that hit the antenna is going to "miss", losing part of the signal. The missing portion of other waves could fill in, but that won't produce as good a signal.

Transmitters have a similar problem. When you put a signal into the antenna, it quite literally zooms up and back down the antenna emitting a radio wave as it goes. Here the antenna should be a multiple of 1/4 of the wavelength or you get part of the signal that doesn't get out of the antenna. Since it can't get out of the antenna, it goes right back into your transmitter. This is called a Standing Wave. In a tiny low power transmitter it is of little consequence. In a larger high power transmitter, you would soon be in need of a new transmitter as this is going to fry your final RF amplifier stage.

What they mean by the same "plane" is that the antenna is either pointing up and down or side to side in the same way as the transmitter's antenna. The radio waves actually orient themselves up and down or side to side. In fact, it is possible to receive two separate signals transmitted at the exact same frequency with two antennas. One mounted up and down, the other side to side. They call this polarization and it is a great way to cram more signal into the same bandwidth. It is even possible to have a circular polarization with clockwise and counterclockwise signals.