08 December, 2011

All I want for Christmas is a nerdy watch

As a self appointed nerd I have a special fascination for watches with binary displays or with morse code readouts. It seems as if such watches now have become designer objects. One reason may be that since everyone has a mobile phone with a clock these days, design can be promoted at the cost of functionality. Anyway, here are some nice watches to choose from for your wish list!

Personally I find the watches from The One to be among the nicest. Here is the Slim Square. The display is a bit hard to read, binary as it is. The trick is that the left-hand side shows the hours and the right-hand side minutes. Then just add up to get the hours and the minutes.

06 November, 2011

Multiple 28 MHz propagation paths and excellent conditions

Final 'F' in UA3MIF. Notice echoes of final dot
marked by arrows. Press image to enlarge.
There were excellent conditions during this weekend's Ukrainian contest. I was active on 10 m and noticed several reverberant signals coming from Russia and Kazakhstan around 11-12 UTC on 6. Nov.

Here is an example from UA3MIF (28 MHz, 11.30 UTC 6. Nov 2011, press link to hear audio) as received on my vertical end-fed dipole (omnidirectional) for 10 m and the K3.  See the picture for the final 'F' in his call sign and what seems to be multiple echoes. The final dot starts at 3.247 sec and multiples seem to occur at 3.322 and 3.373 seconds, i.e. after 75 and 126 ms.

Although 126 ms is almost 138 ms, the round-the-world travel time, I could need some help to interpret these delays based on the locations of the transmitter relative to me near Oslo, Norway. It was easier for a similar reverberant signal from JA3YBK some years ago.

29 September, 2011

Communication with vector potential waves

Field lines (black) and potential (red) for a dipole, static field. 
In QEX July/August 2011 Robert K. Zimmerman (NP4B, VE3RKZ) had an intriguing article entitled "Transmission and Reception of Longitudinally-Polarized Momentum Waves."  What he claims is that he has communicated over a distance of 1500 m at 1296 MHz using vector potential or momentum waves.

Unlike transversal electromagnetic (TEM) waves these are longitudinal waves just like sound waves. This may seem like real magic, but if true it would allow covert communications which is undetectable with ordinary radio receivers and antennas.

01 September, 2011

Elecraft K2 do's and don'ts

In July 2011 Don Wilhelm, W3FPR, suggested that someone ought to write a comprehensive K2 Owner's Manual. This posting does not qualify as one, but at least it lists some things to watch out for regarding the Elecraft K2.
    Minimal stress on the headphone jack
    By all means avoid this situation!  
    • Failing headphone jack: One of the most frequent complaints is the need to replace the headphone jack. Mine has lasted for ten years by being careful not to put undue stress on it. The best thing to do is to use an angled plug for the headphone (left-hand image). Many headphones have that or one can use an extension cord with an angled plug. In either case, this is the best way to minimize the mechanical stress. The worst one can do is surely to put a long mini-jack to jack adapter plug directly into the headphone jack (right-hand image). Replacing the headphone jack is not hard if you follow these instructions from W3FPR.

    13 August, 2011

    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.

    06 August, 2011

    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.

    09 July, 2011

    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.

    17 June, 2011

    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!

    26 May, 2011

    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:

    24 May, 2011

    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

    23 May, 2011

    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).