Wire antennas for DX: Pair of doublets

At my summer cottage (58° N, 9° E), I have two crossed doublets with their centers on the top of a mast as shown in the image. Of course, I would like to have had a rotatable beam antenna, but lacking that, this is a wire antenna substitute with acceptable performance. I use them for DX-ing and participation in contests like the IARU HF contest in July. The first antenna is a 26.8 m (88 feet) doublet and the second one at 13.4 m (44 feet), which was erected last summer, is half this length. Switching between the antennas sometimes makes a difference of 4-5 S-units of signal strength, but usually less.

A regenerative receiver for the 40 m band

I've had a lot of fun with the modified WBR (Wheatstone Bridge Regenerative) receiver which I built Manhattan-style some years ago. The design builds on the receiver described by Daniel Wissell, N1BYT in QST August 2001. Although it doesn't match a good superheterodyne, you get more performance per component than in any other receiver!

Five LEDs in buttons for the Elecraft K2

The Elecraft K2 is quite a small transceiver, made for portable use. Therefore it has fewer indicators of status than many other transceivers. There isn't really much space for this on the rather small frontpanel. But I felt for a long time felt that it should be possible to put additional LED indicators on the K2 but I wanted to avoid drilling holes in the front panel. Here is a method based on using small LEDs in the keycaps, see info from W3FPR/KR5L, as you can always get replacement key caps from Elecraft.

On W3FPR’s recommendation I have used 2 mm LEDs of types HLMP6300 (red), HLMP6400 (orange/yellow), and HLMP6500 (green). They can be bought from Digikey as well as from ELFA in Northern Europe. The first two of the five LEDs that I have added can be connected from the front panel board without additional wiring to other boards.

This YouTube video shows the three first LEDs, the Zero-Beat Indicator, the Split Indicator, and the Audio Filter On indicator:

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’).