Sunday, November 15, 2009


I have started a companion Power Amplifier (PA) for my 43uW QRSS Transmitters, the circuit, as bread boarded, produces about 27mW via Push-Pull output into a 75 ohm load, from a 9Volt Battery, and up to 250mW at 18Volts (two 9Volt Batteries).

In the Experimental Methods spirit of EMRFD, this is a experiment with the following goals:
  • Small as possible (because I like to work on very small things). 
  • Small enough to fit into the centre insulator of my 30m Dipole.
  • Low part count.
  • Low output Harmonics.
  • High Efficiency.
  • Minimum Input Matching Requirements.
  • Minimum Antenna Matching Requirements.
  • Low Idle current between QRSS FSK or CW transmitted messages.
  • Flexible DC Power Requirements, 9 to 18 Volts.
Note: I do not have means to measure or evaluate success of all of the above requirements.

It is of my own design and uses a JFET driver and two 2N7002 FETs for PA's (the black specks seen between the two Toroids). For more power two 9Volt Batteries can be used in series.

Unlike the Oscillator's which uses small 5mil traces, the PA will use a more standard 12mil trace.

I still may do more experiments with different Toroid Turns Ratios for better performance.

The Current Bread Board Configuration.
The 75 ohm Load is standing air cooled :-) on the right.

The PA is designed to support both FSK and CW QRSS from the Oscillator. It is currently a jumble of wires and SMT components, but I have on the computer the PCB layout for a more civilised configuration on a 1x2.2 inches PCB using all SMT parts, including SMT POTs.


Above is a sample output from my local Grabber with CW mode selected on the Bread Boarded QRSS Transmitter.

Currently, the largest component will be a switch, which is used to change modes. It is the smallest switch that I have in the junk box. It is a SPDT, which works OK, but what I really need is a DPDT switch for proper operation.

The Junk Box SPDT Switch

I checked with Mouser, and plan to order a much smaller SMT 611-AYZ0202AGRL DPDT switch.

When finished, I plan to join the Oscillator and PA on a single PCB as a complete Fun and Flexible QRSS Transmitter.


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