The mere fact that CW is no more used by many in the Commercial World and the abolishment of CW as a requirement to obtain a ZS license should not deter you from experimenting with CW as a mode. I decided that the time has arrived to experiment once again with CW. Having passed the 12 wpm CW test years ago and the fact that my CW is completely rusted, I decided to experiment with "controversial" methods of sending and receiving CW. Yes I will be looking into PIC Micro-controllers to produce the CW message string. This might not be acceptable for many but that's just the way it is. Enough rambling, lets get to the practical side of things. I decided to construct a "Flea" Power CW oscillator/transmitter to have fun with. The aim was to build a oscillator/ transmitter:
- with the least amount of components salvaged from old PCB's
- with an RF output power of no more than 10mW
- that can be keyed with a PIC to produce a CW message string
- to determine the distance of reception (mW/km's)
- to experiment with
- that operates on 80 meters
The oscillator/transmitter was constructed using the Manhattan style of construction. The circuit diagram is shown below and is very easy to construct. It only took me 15 minutes to get this "Flea" on the air.
Construction is very simple and to the point. I made my own PCB. The single sided PCB dimensions is 40mm x 35mm. You can even make it smaller if you wish. I used a small drill and made two rectangular blocks (10mm x 5mm) by reaming away the copper. You can also cut two blocks from PCB and glue them onto the PCB with super glue. You will now have the big PCB with two rectangular blocks on it as shown below.
This is your building blocks where all the components will be installed. I first installed the 2N2222A transistor. The collector (C) leg on one block and the base (B) leg on the other. The emitter (E) leg is soldered to the big PCB (Ground) So far so good. You can now install the 50 pF variable capacitor. This capacitor is adjusted to give good keying. Install the one leg to (B) and the other two to ground. If you turn the capacitor upside down you will see that two legs are interconnected and these go to ground while the "live" leg goes to (B). It is now time for the 10K resistor. One leg goes to ground while the other one goes to (B). The crystal I used has a frequency of 3.686 Mhz but you can use a 3.579 Mhz which is easy to obtain. Solder the one leg of the crystal to (C) and the other leg to (B). The 90K resistor is soldered to (B) while the other leg is kept in the "Air" and joined to the 12V (red) wire. The choke is a 2.5mH inductor which you can buy or wind 45 - 50 turns (.5mm dia) on a small ferrite rod. I used what I could salvage from my junkbox and are not even sure of the value. Install one end of the choke to (C) and the other to the 90K leg which is in the "air". All that is left is to install the 350pF fixed cap. One end to (C) and the other to the antenna center pin. You can also use a 400pF variable cap but I opted for a fix capacitor to save space. We are now ready for the smoke test. Connect the 12V (red) wire to a battery and a morse key between the negative of the battery and the ground (big PCB) of the transmitter. No smoke yet.......well if there is smoke than something horrible is wrong. Now get you receiver going and tune to the frequency (LSB) of your crystal. Key the transmitter.....no smoke......good sign. Smoke coming form the transmitter bad sign. You should hear a signal coming from the receiver if everything is working as it should. One word of warning!! This is a very basic QRP transmitter. You will have key-clicks, harmonics and even chirp when using this transmitter. This project should rather be seen as a building block to learn more about QRP transmitters and their behavior. However this "Flea" will get the message out in times of emergency.
Have fun and enjoy!!
