QRPp: Ultra low power operation with the Pixie 2

QRPp is radio amateur jargon for communication using a transmitter with less than 1 Watt power output. That’s less than a handheld GSM mobile phone (max wireless range ~35 km) or a flash light. My Pixie 2 transceiver has so far contacted 15 different countries on 3.5 MHz CW. The first version from 2002 was made in an Altoids tin (picture later), but in 2010 I repacked it in one of the nice clear top tins from the 4SQRP (picture below).

My repackaged Pixie 2

How to make a very cheap VHF receiver

What is the cheapest receiver you can make for VHF? Here is a candidate where all you need to do to modify a small FM headphone receiver is to desolder one end of two capacitors, and connect a short cable with an antenna connector. 

One 22 pF capacitor lifted on the right-hand side near the headphone 

 connector for connection to the external antenna, and another one lifted on 

the left-hand side, above the volume control for increasing the tuning range 

(The receiver IC is on the foil side of the board).

Pixie sidetone oscillator and reduced broadcast interference

This circuit provides a sinusoidal sidetone oscillator for the Pixie. As an added benefit, it will also cause reduced broadcast interference, since the muting circuit of the Pixie is a major source of broadcast interference as the LM386 goes into some sort of nonlinear mode and acts as an old-fashioned crystal detector.

Magnetospherically ducted echo

Magnetic field lines in the
magnetosphere (Ill. NASA)

Signals in the 1.8 - 4 MHz range may pass the ionosphere and be ducted in the magnetosphere out to a distance of several earth radii over to the opposite hemisphere where they will be reflected on top of the ionosphere.

The round-trip time varies with the latitude of the transmitter, or to be more accurate with the position relative to the magnetic Equator. Typical delay times are 140 - 300 ms. At my location near Oslo, Norway, the expected delay is about 308 ms, but unfortunately I have yet to hear such an echo.

Three paths from Japan to Norway along the grayline

The Japanese station JA3YBK was received in Oslo (press here for audio), 30. November 2003, 08:20 UTC on 21.004 MHz during the CQ WorldWide contest. The sound is reverberant due to the multiple copies that are received. This can be seen as extra signals, and it is in particularly easy to see after the first short dot (‘e’ in ‘test’).

Propagation via aurora reflection

Northern Lights in Tromsø, Norway 

Here is a recording of the Swedish station SM6CNN in contact with me on 29. October 2003, 22:42 UTC on 28.024 MHz. The direct distance is about 275 km.

Note the noise-like signal which is typical for signals that have been reflected off the aurora on the higher HF and on VHF frequencies. There was a strong geomagnetic disturbance that day with the K-index at Dombås, Norway reaching a value of 9 which explains the occurrence of aurora reflection.

Polar flutter

Arctic areas

Here is a recording of JW/DJ3KR on Spitzbergen from 24. August 2007, at about 21:45 UTC. This was only a few minutes after I had contact with him on 7.002 MHz.

Notice the fluttery character of his signal. On this day it wasn’t too bad and it wasn’t too hard to copy his signal, but on other occasions, signals that travel over the polar zone may be impossible to copy correctly. The K-index in Tromsø, which lies between Oslo (60 deg. N) and Spitzbergen (78 deg. N), at the time was 0.

[Image source: regjeringen.no]

Moonbounced echoes on 6792.5 and 7407.5 kHz

Recently, a facility with big enough antenna (300 by 365 m) and high enough power (3.6 MW) was used to set a new record for how low in frequency one can go and still get echoes from the moon.

This was also done during the HAARP moonbounce experiment which encouraged radio amateurs to listen on 19 and 20 January 2008. At my location in Oslo, I only heard the direct signal from Alaska, but many in the US heard good moon echoes.