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.

K2 Fixed Level Audio Output

I started by making a very simple modification for a low level audio output with level that was independent of the AF pot setting.

The next step was to modify my front panel board by adding an audio output (mic plug) via a 25 x audio buffer and a zero-beat indicator which uses the same signal. The added circuit is built Manhattan-style on the upper right on the back of the front panel board, see image.

In this way three things are achieved:

1. The amplified audio output is independent of the AF pot setting.
2. The zero-beat indicator is also independent of the audio pot setting.
3. The ‘no-wire’ philosophy of K2 is maintained, as there are no wires that need to be run to any of the other boards.

The schematic of the audio buffer and the updated zero-beat indicator is here. Note that the zero-beat indicator’s component values have some minor changes from the original design, that gave a nicer behavior of the display.

I also have added an optional signal from the sidetone circuit on the K2's control board (requires a plugable strap between the boards). This gives a visual check of the zero-beat indicator when you transmit, and it is also nice for demo purposes as both the received and the transmitted CW are output and can be decoded using e.g. a PC.

My Elecraft K2 Modifications

When I got my license in 2001, I discovered the Elecraft K2 transceiver on the internet and noticed the excellent reviews that it had received. Its receiver outperforms most, if not all, of the commercial rigs on the market. It combines state-of-the art performance with the thrill of building something yourself. It is also important for me that the kit designers encourage experimentation and modification.

My basic K2 with no options, serial #2198, was assembled in August 2001. I have later added the options that are needed to make all the front panel labels meaningful: the KSB2 single sideband option, KAT2 automatic antenna tuner, KAF2 audio filter and real-time clock, KNB2 noise blanker, and K160 160m/2nd RX antenna.