QRP antenna tuner circuit

 

Low power ( 3 to 30 MHz) transmitters constructed by hams are generally called QRP’s. For such transmitters a well tuned antenna is a must.If the impedance is not properly matched there will be a little or no output.But if properly matched there will be great results.A circuit for matching the antenna properly with the transmitter id given below.

The output of the transmitter is given to the input of the tuner( connector BNC1). The output of the tuner(connector BNC2) must be connected to antenna.Then adjust the L1 and C1 to obtain the maximum transmission power.The transmission power can be checked using a SWR meter.

20M 4W QRP Transmitter

 

PIPPIN QRP Transmitter

Basically, it is a conventional Colpitt type crystal oscillator but with the output taken from a low value collector load resistor and direct coupling is made into the base of the PNP device used as an amplifier. The result is a circuit even more simple than the OXO and with considerable advantages.

The small amount of forward bias developed for the PA stage makes it very much easier to drive but is less than the voltage required to actually bias the stage "ON". Keying is in the emitter circuit of the oscillator stage and when the key is up and no current is being drawn there is no forward bias at all on the PA stages.

The isolation of the PA from the oscillator by taking the drive from the low value oscillator collector load, is most impressive and there is virtually no pulling of the oscillator even if the PA load is briefly shorted to ground.

Input to the PA stage runs at 120 to 150mA. at 12 to 14 volts and output on 7Mhz runs at better than 1 watt measured into a 50 ohm load. The PA transistor has a "Stove Pipe" heat sink attached and has been left running continously for more than 1 hour without any complaint from the PA stage.

The collector choke is the usual type and uses 6 turns of 29 swg on two ferrite beads in tandem.