Infrared Transmitter-Receivers

(inside and outside) and that it is possible to run a cable from the window inside to where the radio operator is positioned and a cable outside from the window to a packaged radio with power source. The only problem is how to get through the window!

Infrared Transmitter and Receiver Kit Circuit Board and Components from North Country Radio

IR TX - RX Circuits: This site has a simple diode modulated circuit as well as a more complicated (stable) circuit for a wireless headphone system.

To communicate with a radio, there are three signals required, microphone input to the radio, sound out from the radio and PTT to the radio. Using Infrared transmitters and receivers, it may be possible to transmit audio through the glass. On the inside of the window would be a small unit with an IR transmitter for MIC audio to the radio, an IR receiver for audio from the radio and an IR transmitter for PTT to the radio.

This unit would be attached to the window using a suction cup like the ones used for moving large sheets of glass. On the outside is the opposite configuration with an IR receiver for the MIC signal to the radio, an IR transmitter for audio from the radio and an IR receiver for PTT to the radio.

An alternate approach that may work, is to use a commercial Tone Remote. The control signal for PTT is a tone in the transmit audio path. If this worked, then all that is required is the bidirectional audio paths.

There are some issues such as using short tubes to focus the IR signal to eliminate cross interference and possible use of different wavelengths, to also reduce interference. Some IR circuits simply modulate the diode with the audio, while others are much more stable and use a PLL circuit. With this system, you can go to almost any building and establish a communications system, without running coax through the building and out a door.

Status

EMRG has purchased two sets of TX/RX kits and they are being put together. Some of the thoughts so far, having not tested them yet, are:

1. Will the beams interfere with each other due to reflections in the window?
2. How stable will the TX/RX units be at different temperatures, such as in the winter or summer?
3. Would it be better to design and build a unit with an IF that would allow greater stability and frequency division multiplexing (FDM) to allow more than one system to operate in the same window area.
4. Does the TX/RX system offer any options for short range communications, such as getting across an open entrance way or room without running a cable across the floor or ceiling?