Summary of QRSS QRPp experiment on 40m
2004-11-19 by IK1ZYW

This page summarizes the QRSS QRPp experiment I held on 19 November 2004.
The diagram of the transmitter used is shown in the picture below.

(click for a larger version, 200kbytes)

Circuit description
This transmitter was built using mosly components from the junk box, so the values shown are not mandatory. The oscillator is based on a 14000 kHz XTAL which by chance resonates on about 14002 kHz, then divided by-2 with a JK flip-flop to obtain the signal on 40m.
The power amplifier stage consists of 4 line drivers in parallel (4 out of 8 available on the 74HC240), always keyed. Frequency shift is obtained with the 1N4007 diode in reverse polarization in a sort of "on-off" fashion provided by the NE555 and the extra buffer stage.
You may achieve CW keying by controlling pin 1 of 74HC240, that is the /OE (active on low level) control.
You may remove the squarewave generator at all to obtain a single frequency signal.
You may keep 1N4007 and 220pF cap and substitute 100kOhm+1kOhm resistors with a 100kOhm trimpot to control transmitter's frequency to some extent.

Operating conditions were:
The beacon was battery powered (12V 7Ah gel cell) and located on the balcony where the antenna was hanging from the ceiling. A short length of coax was connecting the transmitter to the antenna. Air temperature was varying between 0 and 15C, but no significant frequency drift was observed. Moreover frequency stability on the short term was extremely satisfactory.
The beacon was enclosed in a plastic box as a protection from birds and moisture.
Positive reception reports with screenshots were received from (in chronological order):

  • 2004-11-19, 0930z, ON6RR in JO20FX
  • 2004-11-19, 1300z, ON5SL in JO10TT
  • 2004-11-19, 1533z, ON6RR in JO20FX
  • 2004-11-19, unknown, DL6JAN in JO60KU
  • 2004-11-19, 1720z-1743z, PA1SDB
  • 2004-11-20, 0830z, ON6RR in JO20FX

    Reception reports measured the frequency being 7001.19 kHz. A sample screenshot:

    Since I am not an expert of 40m propagation, these reception reports teach me that it is possible to cover a 600-700 km hop during sunlight and after sunset for a couple of hours. 100mW TX power probably mean 25 milliWatt ERP in my antenna setup.

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