Mini 100 mW transmitter

Mini 100 mW transmitter

This little transmitter puts out well over 100 mW, using only two transistors. It’s quite

cheap to build, probably under $5,-. At the left is a varicap (20 pF or so). The 27pF capacitor is a small foil trimmer, with 5-27 pF range. At it’s right is a coil (only one), which has 4.5 turns. At 2 turns is a tap, connected to the bf981 source.

If you’d like to use this transmitter on-air, you should add an output filter, the 9 element chebychev (elsewhere on these pages) is a good choice for this. The output is capable of withstanding full SWR for a prolonged period of time. You only have to tune the foil trimmer in the oscillator, the amplifier is broadband.

It’s possible to reduce harmonic output by inserting a 47 ohm resistor with a 100 pF parallel capacitor in the bfr96s emitter lead. This will cause a slight reduction in output power. Supply voltage may be varied from 10 to 15 volts, but frequency and power depend on it! A PLL can be connected to the input. If you wish to use the input for modulation, connect a 100k resistor between input and +13.8 volts. Also use a decoupling capacitor (220 nF) between audio source and transmitter. Sensitivity depends on the varicap, but line level tends to cause overmodulation. For good quality sound, a pre-emphasis is needed (elsewhere on these pages)…

Using this device will probably violate local regulations!

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