FM, AM.. team communication circuit ?

Hi everyone,

I want to transmit different audio signals from different sources and all these sources also have a receiver counterpart
some kind of team communication circuit that allows everyone to simultaneously communicate on the same frequency
a bit like Walkie Talkie or CB, but the simplest circuit possible because not much room and because if it does not work, I am not an RF specialist...

so I read that only AM could allow that cos FM receivers pickup the strongest carrier only, not sure (?)

there are plenty of simple circuits on the web but some say it is FM while it looks AM
https://www.buildcircuit.com/wp-content/uploads/2011/01/Fm-transmitter-Copy.jpg

there are also versions with built-in oscilators like MAX2605 but I dont know wich way to go AM or FM ?

I was wondering if someone could enlight me

thanks

some kind of team communication circuit that allows everyone to simultaneously communicate on the same frequency

Click to expand...

...

so I read that only AM could allow that cos FM receivers pickup the strongest carrier only, not sure (?)

Click to expand...

The idea will hardly work, expect considerable field strength differences, only the strongest signal(s) will actually get through, usually the nearest transmitters. Walkie-Talkies with voice controlled automatic PTT are the usual solution for multi peer communication. Needless to say that the system should also use legal bands and comply to other RF regulations. Home-making a system with apparently no knowledge in RF electronics doesn't sound promising.

its for inside only and just for fun I am planning to make this
but I thought with am, cicuitry should be kept simple and allow multi peer overlaps

Operating multiple AM transmitters on the same frequency will also generate unpleasant interference tones (beat frequencies).

The very simple circuit you posted transmits AM and FM at the same time. Its radio frequency wanders all over the place if you get near it or move away from it and as its battery runs down.

Yes, FM radios have a specification called "capture ratio" that defines how much more strength one signal must be for it to dominate the audio. It is usually small so that if a signal is only a little bit more then it dominates and the weaker one is not heard. That is why airplanes use awful AM that is full of interference instead of clear FM, "Mayday all my engines have stopped!"
Performers use FM wireless microphones that operate on different channels and the receiver receives each channel separately then mixes the audios together. That is what you want but it ain't simple.

Indoors? Then simply scream at each other.

To appear the "capture effect" in FM, the stronger signal should be 3dB or greater than the weaker signal.
Anyway, this is the main reason why airplanes use AM instead FM.
While ago somebody told me that AM is used because was invented 30 years before FM, which in fact is not totally wrong.

rompelstilchen said:

Hi everyone,

I want to transmit different audio signals from different sources and all these sources also have a receiver counterpart
some kind of team communication circuit that allows everyone to simultaneously communicate on the same frequency


I was wondering if someone could enlight me

thanks

Click to expand...

as indicated, simultaneous transmissions on the same freq isn't going to work for FM, AM, or any other analog mode
it's just going to result in a hash of unreadable noise
There are ways to do this digitally, but that starts to get pretty complex to design

you need to reconsider your objectives and methods
if you really want to use FM or AM, you need stable crystal controlled transmitters and receivers that are on DIFFERENT frequencies

Dave

damned... well yeah I could use an arduino and xbee, I guess it would be easier, but more expensive than a couple of discrete components

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what I dont understand is why magnetic waves adding in the air (where the receiver is) would result in so much noise
I am not looking fo hifi audio, as longs as it works, even if the sound has static noise in it

besides if the macgentic fields add up, it should give a natural mixup of everyone based on the distance

also I am using a booster after the battery so the overall power supply never changed until the battery goes out of power (in theory)

The major problem will be to have the identical carrier frequency on all the transmitter. You need to have PLL controlled carrier frequencies. Then we need to worry about the phase. The receiver getting two signals of the same frequency but out of phase will give silence. There will be some other problems. It may be considered like a ghost (a reflected signal) that interferes will the main signal (the stronger signal is being considered as the main).

There will be some more problems.

oh I see, indeed

rompelstilchen said:

.........................
also I am using a booster after the battery so the overall power supply never changed until the battery goes out of power (in theory)

Click to expand...

as written, that doesn't even begin to make sense

rompelstilchen said:

what I dont understand is why magnetic waves adding in the air (where the receiver is) would result in so much noise
I am not looking fo hifi audio, as longs as it works, even if the sound has static noise in it

besides if the macgentic fields add up, it should give a natural mixup of everyone based on the distance

Click to expand...

ohhh and it's Electromagnetic fields not just magnetic fields


beg, buy, borrow a copy of the ARRL Handbook for amateur radio and start doing some serious learning about
radio transmission and reception etc

Dave

Two separate electromagnetic waves can combine if their frequencies are identical, they are in phase and have the same polarization. If they are having different frequencies, you will hear modulation which will cause warble. If they are out of phase, you will lose signal strength. If they have different polarization, they may be received with different strengths (depends on the orientation of the receiver). For both the receiver and the transmitters are stationary then some arrangements may be worked out. You are out of luck otherwise.

Consider a simple LC tuner with a simple straight wire antenna. With stationary transmitters, you will be able to receive both signals. Consider a simple diode detector. You will hear AF from both transmitters. As soon as move the receiver, you will see severe distortions and/or modulations.

AM will be somewhat better (because of their long wavelength) for your goals but the results will be uncertain.