Radio Frequency Close connection

[dleebell]

Hi

I've got a project, where I'm using a one way Radio frequency system between 2 devices (Similar like a baby monitor).

At certain points of using the 2 devices they will be together, so touching physically side by side. I know with walkie talkies if you put them close together they create noise.

I have two concerns:

Are they still able to send information to each other without interference of one another?

Are you able to get rid of the noise interference by disconnecting the speaker on one of the devices without affecting the information that is sent from the frequency waves?

Or is there an easier way of getting rid of this noise without affecting the information being transmitted from one to the other.

Many Thanks
Dominic

[w2aew]

There are two main problems that arise (and a host of others) with a transmitter and receiver placed close together. 

The "noise" you mentioned when placing walkie talkies together is due to simple audio feedback - an audio signal from the speaker on the receiver being picked up by the transmitter's microphone - resulting in some "positive" feedback which results in howling or squealing most often.  For this scenario, disconnecting the speaker or muting the receiver will usually stop the interference. 

The second most common effect is overload of the receiver which happens if the receiver and it's front end, AGC, etc. are not designed for the high signal strength that occurs when the receiver's antenna is so close to the transmitter, thus coupling a very high signal level into the receiver.  The only way to combat this is to reduce the coupling between the devices (shielding the antennas from one another, removing the receive antenna, dropping the tx power, etc.).

The other things that can happen can be more complex, with things like the transmit signal begin coupled into the LO and IF stages in the receiver, etc.  The extent and side effects of this type of thing will vary greatly with the design and function of the devices being used.

[dleebell]

Hi w2aew

Many thanks for your reply.

The "noise" you mentioned when placing walkie talkies together is due to simple audio feedback - an audio signal from the speaker on the receiver being picked up by the transmitter's microphone - resulting in some "positive" feedback which results in howling or squealing most often.  For this scenario, disconnecting the speaker or muting the receiver will usually stop the interference.

Ok so because the neither of the two devices that I have microphones they only have speakers, does this mean I won't have any interference?

The second most common effect is overload of the receiver which happens if the receiver and it's front end, AGC, etc. are not designed for the high signal strength that occurs when the receiver's antenna is so close to the transmitter, thus coupling a very high signal level into the receiver.  The only way to combat this is to reduce the coupling between the devices (shielding the antennas from one another, removing the receive antenna, dropping the tx power, etc.).

1. shielding the antennas from each other: would this make this more difficult to send information to one another?
2. Removing the receiving antenna: Does this mean it can still recieve information from the transmitting device? In this case can it be that theres a switch to disconnect it?

My basic design, is one device with buttons (Each with a different tone frequency) that transmits information to the receiving device which   in toll processes it and plays it on that device.

Many Thanks for your help again.

Dom