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80-M Amateur Radio Transmitter

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This transmitter consists of a keyed crystal oscillator/driver and a high efficiency final, each with a TMOS Power FET as the active element. The total parts cost less than $20, and no special construction skills or circuit boards are required.

The Pierce oscillator is unique because the high Crss of the final amplifier power FET, 700-1200 pF, is used as part of the capacitive feedback network. In fact, the oscillator will not work without Q2 installed. The MPF910 is a good choice for this circuit because the transistor is capable of driving the final amplifier in a switching mode, while still retaining enough gain for oscillation. To minimize cost, a readily-available color burst TV crystal is used as the frequency-determining element for Q1.

An unusual 84% output efficiency is possible with this transmitter. Such high efficiency is achieved because of the TMOS power FET's characteristics along with modification of the usual algorithm for determining output matching.


Parts List:
Component: Value: Datasheet: Qty:
Resistor

2K Pot, W

Not Available 01
Resistor

2K, W

Not Available 01
Resistor

1K, W

Not Available 01
Resistor 30, 3W Not Available 01
Resistor 62, 1W Not Available 01
Capacitor 0.01uF Not Available 01
Capacitor 180uF Not Available 01
Capacitor 0.01uF Not Available 01
Capacitor 1310pF, 500V Not Available 01
Capacitor 0.1uF, 100V Not Available 02
Capacitor 105pF Not Available 01
Crystal 3.5795MHz Not Available 01
Fuze 3A, FastBlow Not Available 01
Inductor 2.08uH Not Available 01
Inductor 3.43uH Not Available 01
Diode 1N3044 Not Available 01
? MTP12N10 Available 01
? MPF910 Not Available 01