Matchbox Radio Line

The Line: paddle – keyer – TRX – power supply - all in their covers …




and in operation connection

The Paddle




Two brass plates 34x34x3 mm give the base and the top (and the weight, too) kept together with 3 brass spacers which have M3 screw thread. The paddles are made from a piece of red plastic. They are squeezed together by a longer M3 screw and a spring. With an M3 nut you can change the pressure. Two little screws at the end are the dot and dash contacts, since they are fairly tough in their hole they offer a sensitive adjustment within a fraction of movement for a fine CW feeling. The complete paddle with its 54 mm length fits into a matchbox cover.

The Keyer

The code I wrote is in assembler and I used it in many older projects with different controllers. Here is a small 8-Pin device with an internal clock. Look here for the source code or assembling hex-file. R1 is a pull up resistor, this pin has no internal one. The side tone on pin 6 leads to a piezo element. Pin 7 keys the transmitter via the Mosfet Q1 .




Change the CW speed by pressing the speed button and than use the paddle as up/down keys, in the same manner you can change the side tone. If you hold the speed button and switch the keyer on, the cq machine will start. If a call is done – break in with the paddle or wait for a next call. A simple text input routine on the other button is ready. Here the description.

The TRX

Less than 25 parts but difficult to find the right dimension. The idea comes from G3XBM in SPRAT 151. I built this little TRX for the 30 m band. The parts around the transistor T1 is the XO and the self mixing stage for the RX. Because of the very high resistor on the emitter the stage produces a very small RF amplitude. Via C3 the AF is coupled to a 2 stage AF amplifier. Set the value R5* that the collector T3 shows about the half of the value of the power supply. The AF gain is more than enough so you can attenuate the antenna line, that avoids RF break through.




If the key line is grounded the resistor R3 changes the operating point T1 and it runs with about 300 mW output. The AF stage is nearly shorted and the headphone is rather quiet. The problem was the RIT. The crystal frequency shifts only a few Hertz between RX and TX mode. So I reduced C0 and added a varicap D1 from the junk box. The DC level on the base T1 changes a few volts between RX and TX and D1 gives more C or less C parallel to C0. I searched a varicap and changed C0 so that it gives me about 1 kHz RIT. Keying via a reed relay offers more stability than a keyer with a long cable. I made a high impedance headphone from two piezo modules and an old walkman headphone. The impedance is about 5 kOhm and no output capacitor is needed. Only a little more selectivity around the 1kHz could be desirable.

The Power Supply

At the moment 6 Li Cells deliver 18 V but they have a high internal loss (and a high electrolytic capacitor is needed). I will replace this with another solution in the future.







And the results:
Without the RIT I had no QSO, I only saw my signal Europe wide on Reverse Beacon Network. On the very day I included the RIT, I worked SM5, he gave me 569, and LZ, a 599 station no real rprt but he heard me fairly well,… all in a few minutes.