05 September, 2014

So you want to play with a Pixie 2?

My own surface mount version of the Pixie2
Here's a guide in table format to minimalistic single-band amateur radio transceivers. The Pixie 2 and related kits are fun to build, yet they perform well enough to be used, although with some effort, for real contacts.

The idea of using the power amplifier transistor as a mixer seems to come from George Burt - GM3OXX - whose five transistor FOXX was described in 1983 in SPRAT. The basic design of the oscillator, PA/mixer and the simple keying has been more or less unchanged since Oleg Borodin - RV3GM - described the four transistor Micro-80 in 1992 in SPRAT. Then Dave Joseph - WA6BOY - replaced two of those transistors with the LM386 audio amplifier in the Pixie 2 (QRPp 1995). Most later versions are variants of these designs.

Here's the table of Foxx, Micro 80, and Pixie 2 kits:

20 August, 2014

Digital Signal Processing

The Norwegian-language "The road to the international radio amateur license" came off the press this June. It is based on the RGSB International Amateur Radio Examination Manual from 2006, which RSGB graciously allowed us to use.

But the translation has been adapted on several topics. One example is the chapter on propagation due to the need in our country for more emphasis on propagation in polar regions and in mountainous terrain. Another is a completely new chapter on digital signal processing.

15 August, 2014

New gadget measures negative resistance

If you are like me, you appreciate electronic gadgets with dials and displays. So when I discovered this "USB detector",  I thought to myself that I really always wanted to know the voltage as well as the current consumption of my USB devices. And since it is more or less impossible to connect a multimeter, this is exactly what I need.

The device fully satisfied my curiosity. Actually one surprising result was that the charger for my Samsung Galaxy Note 8 has a negative output resistance.

07 August, 2014

WSPR on 5 bands

For the first time ever I have been spotted on all the five bands that my Ultimate3 QRSS/WSPR kit (G0UPL design) is transmitting on. This is after 2-3 days of transmitting.


Right now I am using the beacon for discovering if the bands should open up on 24 and 28 MHz. The other three bands, and especially the 14 MHz band, serve as references to tell me that the transmitter is working. My antenna is not so optimal so I would be surprised if I am spotted far outside Europe. It is an end-fed 5 m long half wave vertical dipole which isn't too bad for 28 and 25 MHz, and probably not very good at all on 21, 18, and 14 MHz.

02 August, 2014

Nice radio-related stamp

A few weeks ago I had one of my rare visits to the post office. As I was waiting, I saw a display of a new series of stamps and I just had to buy the one shown here. What caught my attention was not really the artist, but rather the Kurér portable radio.

The stamp was of course not about the radio but was issued in commemoration of the 100 year anniversary of the birth of Alf Prøysen. The English Wikipedia page has this to say about him:

20 June, 2014

Disappointment with Spice and the QRP-er's favorite, the LM386

The trusty old LM386 audio amplifier from the 70's is still used a lot in low power and portable equipment. Recently some ultra high gain circuits have been recommended that I wanted to simulate with Spice. I started with the datasheet examples for checking the quality of the model. The result was surprising.

In the data sheet one can find a minimum parts circuit, a high gain circuit, and a bass boost circuit:
Gain = 20 (26 dB), minimum parts
Gain = 200 (46 dB)
Bass Boost









30 May, 2014

Temperature compensation for an Arduino ultrasonic distance sensor

161.3 cm
27.0°  347.7 m/s
Ultrasonic distance sensors can find the range out to 2-4 meters and are popular in e.g. robotics. Here I look at how the accuracy can be improved by compensating for the variation of speed of sound with temperature. It actually varies quite a lot in air and around 0 C it is:

      c = 331.3 + 0.606 * T

where c is in m/s and T is in C. The formula is good to up to at least +/-30 C. There is also a dependence of humidity, but as it is so small it is neglected here.

The equation can be analyzed for sensitivity (a little bit of differentation, you know). The result is that a two-way range measurement creates an error of 1.8 mm/C/m. That means that with a 4 degree C error, the deviation will be 14.4 mm at a range of 2 meters. Not a lot, but more than the wavelength which is 9 mm at 40 kHz. Considering how easy it is to compensate for, then why not give it a try?

19 May, 2014

Nice, watery CW signals from Alaska

 Great circle path between Anchorage and Oslo
Here's what a transpolar signal sounds like (click here to listen) and looks like (below). This one has traveled from Anchorage, Alaska to Oslo, Norway.

The characteristic sound of a CW signal that has passed over a moderate geomagnetic disturbance (Kp = 2) isn't too hard to recognize with a little practice. There is also some static on this short recording as we had a local thunderstorm coming in with the first summer days here.

The great circle distance between the two cities (actually their two airports) is 6446 km as illustrated by GPSVisualizer. Anchorage and Oslo are about at the same latitude, 61° N and 60° N, respectively. As they are at longitudes 149° W and 10° E, there is a difference of 159 ° - almost 180 ° - and this means that the signal almost passes directly over the North Pole, although a bit hard to see on the projection used in the map.