FM transmitters

[baz123]

I have a cheap FM transmitter for listening to an mp3 player from a radio and the range seems remarkably good, it can be picked up by neighbours on either side of my house.

I wondered if by using multiple fm transmitters all connected and broadcasting simultaneously from the same device I may be able to increase the range even further i.e would 2 transmitters send the signal twice as far as one transmitter or does it not work like that?

I apologise if that's a stupid Question but any enlightenment would be hugely appreciated.

 

[crutschow]

Since the transmitter RF frequencies would not be exactly the same, then their outputs would tend to interfere with each other and likely reduce the range over just one transmitter.

 

[Hero999]

Use a better aerials on both the transmitter and receiver(s).

 

[baz123]

factory preset

Thanks for your swift reply!
My transmitter only has 4 preset output frequencies if I were buy another device the same why would they not be identical?
Or again, am I missing something?

 

[baz123]

I thought I might install better aerials too if multi transmiters were to work.

 

[Hero999]

Thanks for your swift reply!
My transmitter only has 4 preset output frequencies if I were buy another device the same why would they not be identical?

It's impossible to make two devices which are completely identical, there will always be a slight difference in frequency between two different transmitters, even of the same make and model.

Another thing is the two transmitters won't be in phase with each other.

Herre's an analogy: take two digital clocks and connect them both to a power supply simultaneously. First of all you'll notice they will not be both in time with each other, one will be a fraction of a second ahead of the other and after a while they will gradually drift and display completely different times. This is because the two clocks aren't exactly the same.

The same is true for the transmitters, the problem then is that the signals will interfere with each other: some parts of the signal will add others will cancel which will create distortion. Think of the waves being produced and what would happen if two slightly different waveforms are superimposed on one-another.

 

[baz123]

" some parts of the signal will add others will cancel which will create distortion. Think of the waves being produced and what would happen if two slightly different waveforms are superimposed on one-another."

Thanks, that did it for me!

You're right there's no way any 2 of these devices will be quite the same- cheapest of the cheap!

**broken link removed**

Great value for money though, although I can't believe they're legal with such good range.

 

[audioguru]

Your FM transmitter probably has an attenuator feeding its antenna to reduce its range so it does not cause interference to your neibours.

 

[transistor495]

4 preset frequencies or 4-DIP switch with a combination upto 14 possible frequencies? It may be BH1417 stereo transmitter.

It is fairly possible to increase or decrease it's power..