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Experiments with UHF transmitter modules

UHF transmitter and receiver modules are used for a wide range of short range applications such as remote control or slow speed data transmission.

A common frequency used is around 433.9 MHz, which puts it inside the amateur 70cm amateur band. While their use can interfere with amateur activity in our case having these modules operate within our band means that amateurs have a head start when it comes to equipment and antennas to experiment with them.

The modules I had were marketed as data modules. My early experiments were to get them to transmit sounds and then AM or FM voice. This was successful but I found that some settings, such as the bias voltage on the module's data input connection, greatly affected transmission frequency and modulation quality.

The transmitter modules are designed for use with superregenerative receiver modules. Both have very short antennas designed for limited range. But if you were to use amateur gear with good antennas then the modules can transmit surprisingly far. Especially if you're able to put them on a frequency less prone to interference from other low power devices. Watch the videos below for further details, including circuit diagrams and range tests.

Demonstrations of UHF transmitter modules

Introduction

  Attempts at transmitting voice

  Adding a 555 audio oscillator

  Clearer AM and FM voice transmissions

  Even better AM and FM voice transmission

  Another range test with UHF modules

  Adding an electret microphone to UHF transmitter modules

  AM voice transmissions to companion UHF receiver module

  Using a flashing LED to give distinctive keying

  Possible useful items for UHF module experiments

 

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