My first homebrew QRP TX was a simple solidstate CW transmitter using SL100, SK100 and BD139 giving about 5Watts on 40 Mtr band. This circuit was popular in South India and was known as ' VWN' circuit.
- A RFC similar to the one used in the VFO circuit is used in SK100 collector to ground end.
- BD139 Tank coil is 4.4 uH and is wound with 24 swg enameled copper wire on a piece of polythene pipe of 1.7 cms OD & lenght 3 cms. Tap at 13th , 15th and 16th turns. 13th tap can be used for 50 Ohms coax/ inverted 'V' Ant or 15th tap can be used for 75Ohm coax/ Dipole Ant.
- Mount BD139 on a heatsink.
- Keep input current (BD139) at less than 200mA.
I also have made a vwn transmitter fixed on 7058kc with help of pre-mixed xtal oscillators. Would like to see your results and i had some problem in loading into the antenna. have a look. vu3inj.blogspot.in
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