Wednesday, September 8, 2010

My 30m QRPp MEPT

After a long & detailed theoretical description of the subjects that rely on the QRSS – QRPp experimentation field of amateur radio, today I will present you my 30m QRPp MEPT. Although I have a long experience with QRP and QRPp experiments via 2-way QSOs, this is my first attempt to experiment with QRSS on QRPp levels via Manned Experimental Propagation Transmitters (MEPTs). My MEPT operates inside the QRSS window of the 30m HF band (10140.0 - 10140.1 KHz). The circuit consists of two units: the transmitter and the keyer. The transmitter is based on two bipolar NPN transistors that the first works as a Colpitts oscillator and the second as a buffer and one N-Channel FET that works as a low power amplifier. The transmitter circuit is 80% identical to the 30m QRSS Kit designed by G0XAR & G0UPL. The transmitter's amplified signal is filtered with a 7 element Chebyshev low pass filter based on the short guide to harmonic filters of G3RJV. The bias of the N-Channel FET has been calibrated to produce an output of 8Vp-p @ 50Ohms that is equal to 160mW.

The keyer unit is based on the AT90S2343 AVR RISC microcontroller produced by Atmel. The microcontroller is configured to run with the internal RC 1MHz oscillator and is programmed with the appropriate firmware (written in BASCOM-AVR from MCS Electronics) to produce a repeated slow morse cw message with my callsign "SV8GXC". The dot length was programmed to 3 seconds. The cw-key output of the microcontroller drives a reverse polarized red LED that works as varicap and shifts the oscillator frequency to about 8Hz. The final result is an FSKCW3 signal at 160mW.

The above MEPT was tested in lab and soon will be on the air for experiments in collaboration with the QRSS Knights group. It will be tested for some days on FSKCW3 and the results will be presented in the next post. Stay tuned!

[1] G0UPL, 30m QRSS Kit,
[2] G3RJV, A short guide to harmonic filters for
QRP transmitter output,
[3] Atmel, AT90S2343 Datasheet,
[4] MCS Electronics, BASCOM-AVR,

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