Mobile Phone Conversion

Several fellow hams in the Asker and Bærum district have converted Mobira (Nokia) MD50 or MD59 Talkman NMT-450 phones from 1985-1988 to the 70 cm band. LA7TM, Nicolai, has played a central role in the conversion, based on the work of Finnish hams who pioneered the conversion and made their experiences and their software available. We then made some changes to the software. These changes are now included in the official Finnish version.

Remapping of Keyer Speed Pot Range for the Elecraft K2

I am beginning to realize that I will never be able to exceed 20-25 wpm CW speed. The speed pot of the K2 however covers from 9 - 50 wpm with 30 wpm in the middle position. Thus the range which is useful to me is just a small fraction of this range.

In order to map 9 - 25 wpm to a larger range, one can add a series resistance to the pot, but this is cumbersome and requires cutting traces on the front panel bord. One could also change the speed pot to a logarithmic one, but this is also a rather involved operation. My solution was to emulate a logarithmic pot by soldering a 2.2 k resistor between the wiper and the CCW end of R1 on the Front Panel Board, the 5K Keyer Speed pot. In this way the pot stills covers the full range from 9-50 wpm, but 22 wpm is now in the middle position. See image for where the resistor is located. The left-hand wire can be found right under the G in "MIC CONFIG." (Note that the Manhattan-style circuit board to the upper right is a fixed level audio output and a zero-beat indicator).

If one had used an even smaller resistor than 2.2 k one could make the low speeds cover an even larger range of the pot, but I don't recommend this. In contrast to substituting a log pot, the added resistor makes the pot load the circuit more as the pot is turned in the clockwise direction, so that instead of 5 k load, it now presents 5 k in parallel with 2.2 k or about 1.4 k. I would not recommend loading the control circuit even more.

Elecraft K2: Using the KPA100 loudspeaker when the KPA100 is remoted

When the KPA100 power amplifier is external to the K2, the KPA100 loudspeaker is unused. I wanted to use it for other rigs that need a loudspeaker. The minijack connection on the back of the KPA100 can be used if its internal switch is shorted.

This can be done in a simple way by mounting a male header and plug in the unterminated "AF In" connector (J5). The lower pin on the header should be soldered to the warm speaker cable. See middle right in the image (press image to zoom in).

If the KPA100 is mounted in the K2, J5 is plugged into the K2 main board, and when it is used stand alone, J5 may be plugged into the new header. In this way the KPA100 loudspeaker connection is compatible with the original design when mounted in the K2, and its loudspeaker can be used for other rigs when the KPA100 is separate from the K2.

Be sure to measure the resistance at the end of a mini-jack cable plugged into the external speaker connector before trying the loudspeaker. It should measure about 4 ohms, and if it is less than 1 ohm you have made a short to ground, so check the header once more.

25 part transmitter for the QRP Minimal Art Session

My Minimal-Art-Session rig shown here was made for class B of the QRP-MAS competition which is in May every year. In class B the transmitter should have a maximum of 50 components, and the fewer the number of components, the more points one will get per contact. With such simple rigs, only CW is viable.

This rig was made by combining ideas from several designs that I had seen and it was finished the same day as the competition. I ended up with 22 components in the transmitter except for the output filter. The rules say that no matter what, the output filter counts as three components. I guess this is in order that no one is tempted to simplify the filter too much and start emitting harmonics. 

Adaptation of some Morse programs to Norwegian

Nice drawing of Bencher keyer by Dutch radio amateur
Dick Kraayveld, PA3ALM
(http://www.morsecode.nl/pa3alm.html)

Norwegian has three special characters that need to be learnt as well: æ, ø, å.  Therefore I adapted some Morse programs to Norwegian in 2001 when I learnt Morse myself. The programs are found below: 

• Training program using the Koch method. Excellent for learning the symbols for the first time. Unfortunately this program gives too long spaces between dashes and dots as the speed approaches 12 words per minute.
• Simple text to Morse program
• Norwegian files for "The Mill". This is one of the best Morse practice programs, it has everything except that unfortunately it does not have a simple window based user interface. Do the following:
• First download and install The Mill made by Jim Farrior, W4FOK
• Then there are two alternatives:
1. Either replace the two files #26.rwd and #26.rwd which are in the archive MillNorsk.zip. They will add 100/400 Norwegian common words to the English ones in the menu for code practice of the common words.
2. Or add the two files 100norsk.txt and 400norsk.txt to the Mill00a folder with the other program files. To use the Norwegian files select from the Random Word Sender Menu 9 -List of other available files, and type in the file names (suggested by Jim Farrior).
• Either alternative makes it possible to practice the Norwegian/Danish characters æ (.-.-, = Swedish/German ä), ø (---., = Swedish/German ö) and å (.--.-).

I can unfortunately no longer maintain these programs. A good alternative now is Just Learn Morse Code by LB3KB. It also supports international (non-English) letters.

QRP Antenna Tuner

My 75 meter horizontal loop antenna is tuned by a home-built Z-match antenna tuner, a slightly modified version of the Norcal BLT (Balanced Line Tuner), with a resistive SWR-bridge using a super-bright LED. I could tune my 75 m loop on all bands up to and including 20 m, but at higher frequencies I could not get the series capacitor small enough. The cure was to add a switch to choose between the original primary coil with 8 + 8 turns or taps at 4 + 4 turns, after an idea by DL8RAM. This is selected by the 80-20/20-10 m switch and comes in addition to the switch between Hi-Z/Lo-Z on the secondary (the output). This tuner also tunes a 13.4 meter doublet well on 40-10 meters.

I designed a frontpanel layout for the tuner. It was generated from a text file using the program of WB8RCR. I would recommend this program for any homebrewer who wants to improve his panel layouts. I print mine on paper,

Unleashing the LM386

From Wikipedia Commons, author 'Samba pa ti'

The LM386 must be one of the most popular audio output amplifiers among radio amateurs, despite having been around for a long time. It's an IC which even has its own Wikipedia page. The LM386 can be obtained in both dual-in-line and surface-mount packages and outputs 325 mW in the standard version that runs from 4-12 Volts supply voltage.

Its voltage gain of 46 dB is in many cases too little, especially in direct conversion receivers. When I built the Pixie 2 with the LM386 audio stage, it struck me how the sensitivity of the receiver was limited by the audio gain. I asked myself if it would be possible to increase the gain and add some filtering in a simple way. The result is a gain of more than 70 dB and an audio bandwidth of a few hundred Hz by only adding 5 passive components to the standard circuit: 3 resistors, 1 capacitor and an inductor.

Inductance and capacitance adapters for a digital voltmeter

The adapters have been built from the drawings in chapter 26 of the ARRL handbook for radio amateurs, 2000, using the ARRL PCB templates. They convert capacitance/inductance to mV to read on a digital voltmeter: Capacitance is in two ranges: 2.2-1000 pF or 1 – 2200 nF, and inductance in these two ranges: 3-500 uH and 0.1-7 mH. The projects can be found here.

Errata for the capacitance adapter:

• The PCB template is incorrect. There is a connection between pin 7 of U1 (ground) and the minus connection of the DVM that needs to be cut away. In the template, the trace from pin 7 going down for a few mm and then to the right should only go to the next hole where the strap is soldered. Then it should be cut, and not be allowed to connect to the junction of the parallel capacitors C5 and C7 (whose sum make up 0.2 uF).

Recommendation for the inductance adapter:

• There are sharp pulses in the supply voltage unless a couple of decoupling capacitors are added as in the capacitance adapter. The values are not critical, e. g.: 10 uF/10V on the 9V supply, and 1.5 uF/10 V on the 5V supply.