Two or more antennas transmitting on same frequency

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tupanka

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Hi, My question is: what happen if I have three FM trasmitter working on same frequency but each one of them transmit a different audio file? My idea is to use a radio fm headphone to capture different FM signal from different fm transmitter located in a room. Is possible to move your position to switch from a signal to another remaining on same frequancy or I'll have a sort of interferience or distortion?
Thanks
 

lmrtek

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RF works by the capture effect so you will likely hear none of the transmitters and only a jumble of noise.
 

MaxK98

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The only way you will be able to broadcast multiple messages on one frequency with one transmiter is with TMDA, timed multiplexing. Otherwise, if you really need three transmitters, you can sync them to transmit one at a time with some kind of controller.

Care to share your project structure and goals? THere might be betters ways.
 

wtp

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ahhhh...

stereo does not work that way.
how about one FM stereo transmitter with the audio split one to the left, one to the right and one
mono sent to both.
it might get a little weird to listen to.
 

RFBOSS

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RF works by the capture effect so you will likely hear none of the transmitters and only a jumble of noise.

For those following along, it is more accurate to say that FM receivers, not RF in general, have a characteristic that is called their capture ratio. That is an FM receiver will capture the strongest of two or more signals and ignore the rest.

The specification is called the capture ratio (the relative difference between the signal captured and the rest of the signals on the same frequency). This ratio is expressed in dB. Some FM receivers are much better at this than others.

In the OP's situation, the relative signal strengths of the three transmitters may to be close enough to each other to cause problems.

Now having said all of that...

It depends on the relative separation of the transmitters and FM receiver and the quality of the FM broadcast band receiver.

There are likely to be a number of variable involved. Depending on the size of room, the position of the transmitters and their relative RF outputs, reflections and so on, it might be possible to make this work okay.

For example if the distance to the receiver for one of transmitters is 20 feet and to the other is 10 feet, the difference in signal strength would be about 6 dB. It is not uncommon for an FM broadcast band receiver to have a capture ratio in the range of 2 dB. In this case the receiver would likely lock onto the stronger signal (closer transmitter) and ignore the weaker signal.

Again there are a number of variables involved that could complicate things, but with a little thought put into the layout of the transmitters relative to the listening positions it might be possible, but there are no guarantees.
 

slicerwizard

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Hi, My question is: what happen if I have three FM trasmitter working on same frequency but each one of them transmit a different audio file? My idea is to use a radio fm headphone to capture different FM signal from different fm transmitter located in a room. Is possible to move your position to switch from a signal to another remaining on same frequancy or I'll have a sort of interferience or distortion?
Thanks
This would pretty much require a very highly directional antenna system. You'd be better off using modulated light and a directional sensor, i.e. a light sensor covered with a tube.
 

prcguy

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What the OP wants is doable wth very low power transmitters. Disneyland did this with their "Main street electrical parade" where they had low power transmitters along the float path with different theme music for each area.

As the floats progressed along the route a squelched receiver would pick up a certain broadcast for a short distance, then go quiet, then it would pick up the next broadcast 100ft or so away. I've heard of people getting into the VHF band wireless mic freqs with modified ham radios and lighting up all the floats with whatever they wanted to say over the radio because the ham radio had a lot more power and range than the low power them music transmitters.
prcguy
 
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