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.
04 November, 2006
16 March, 2006
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.
21 January, 2006
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.