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!
Link Hero will be back soon
Thank you for being patient. We’re making LinkHero better than ever 🙂