DIY Micromitter Stereo FM Transmitter

Posted on Feb 5, 2014

This new stereo FM Micromitter is capable of broadcasting good quality signals over a range of about 20 metres. It`s ideal for broadcasting music from a CD player or from any other source so that it can be picked up in another location. For example, if you don`t have a CD player in you car, you can use the Micromitter to broadcast signals from a p

DIY Micromitter Stereo FM Transmitter
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ortable CD player to your car`s radio. Alternatively, you might want to use the Micromitter to broadcast signals from your lounge-room CD player to an FM receiver located in another part of the house or by the pool. Because it`s based on a single IC, this unit is a snack to build and fits easily into a small plastic utility box. It broadcasts on the FM band (ie, 88-108MHz) so that its signal can be received on any standard FM tuner or portable radio. However, unlike previous FM transmitters published in SILICON CHIP, this new design is not continuously variable over the FM broadcast band. Instead, a 4-way DIP switch is used to select one of 14 preset frequencies. These are available in two ranges covering from 87. 7-88. 9MHz and 106. 7-107. 9MHz in 0. 2MHz steps. We first published an FM stereo transmitter in SILICON CHIP in October 1988 and followed this up with a new version in April 2001. Dubbed the Minimitter, these earlier versions were based on the popular Rohm BA1404 IC which is not being produced any more. On both these earlier units, the alignment procedure requires careful adjustment of the ferrite tuning slugs within two coils (an oscillator coil and a filter coil), so that the RF output matched the frequency selected on the FM receiver. However, some constructors had difficulty with this because the adjustment was quite sensitive. In particular, if you had a digital (ie, synthesised) FM receiver, you had to set...

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