Thursday, 10 March 2011

VWN homebrew QRP TX


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.

1 comment:

  1. 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.