Small voltmeter for a QRP rig

AT Sprint rig in an Altoids box, itself contained in a video case.
Digital voltmeter in lower left corner shows 12.0 Volts.
(Click for larger image)

Every battery-operated rig needs a voltmeter. I had a small analog voltmeter for my AT Sprint QRP (= low power), 4 Watt rig, but after it failed I wanted to upgrade it to a digital one. I found a miniature meter on Ebay which is perfect for a QRP rig and which I recommend.

Aurora, 50 MHz and the Elecraft P3

Tonight had nice aurora conditions on 6 meters due to a geomagnetic storm. The Elecraft K3/P3 combo did an excellent job in showing how wide the bandwidth of these CW signals has become after having been reflected off the aurora.

The first image shows the green cursor on SM7FJE's signal, the bandwidth is almost 1 kHz.

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.