[Photo] Self-made QRP CW transmitter

Homemade QRP CW transmitter

CW (ConTInuous Wave) constant amplitude telegram is the oldest communication method. It usually uses the famous Morse code to communicate. Compared with other modulation methods, its biggest advantage is its strong anti-interference ability. As long as the power is small, you can enjoy the fun of DX communication.
There are many QRP clubs abroad. The original meaning of QRP was: "Shalll reduce power?", Which was later extended to low-power operation. For CW transmitters, QRP means that the auxiliary output power does not exceed 5W. Foreign QRP enthusiasts usually make their own output power of hundreds of mW or even smaller QRP CW transmitters to communicate. They regard this as a challenge. There are many foreign awards dedicated to QRP enthusiasts.
The QRP CW transmitter is small in size, simple in line, easy to obtain materials, and suitable for self-made. It can be built for a few tens of yuan plus a few nights. Due to the small output power, the auxiliary matching filter network does not need to be made of high-voltage capacitors, and has little impact on the environment, which is not easy to cause harmonic interference. Due to the small operating current, it can be powered by nickel-cadmium batteries, so it can be easily taken to the wild (Eg: high mountain top) can be operated for a long time for operation.
The communication distance of QRP CW transmitter is related to many factors. Such as the performance and location of the antenna, operation skills (such as the choice of working frequency band), etc., but it is not a rare thing to use only 50-100mW output power for 800-1600 kilometers of communication. There is an amateur radio station in Shanghai 2P QRP CW transmitter was used to successfully contact South America.
With little money to make a QRP CW transmitter, you can make many friends in the world, improve your English, and improve your practical ability. Why not do it?
This is a very representative classic ORP CW transmitter circuit, only need to replace the value of some components according to Table 1, can work in various bands in the HF band. The crystal oscillator is composed of 2N2222 as the main vibration group. C2 can be used after the operating frequency is higher than 80 meters. It is replaced by the inter-electrode capacitance inside 2N2222. T is a wide-band transformer wound on the magnetic ring to perform impedance conversion between stages. The primary coil of T and C3 together form a tuning loop. Because T cannot be adjusted, it can only be tuned through C3. Because the input impedance of the power amplifier stage is low, in order to ensure that the tuning loop has a high Q value, and in order to reduce the burden of the upper vibration stage to improve frequency stability (excessive burden may even stop the oscillator), T should have A higher impedance ratio (impedance ratio equals the square of the turns ratio), so T cannot be replaced with FCZ coils. The secondary coil of T only needs 3 to 5 turns, because the lower the frequency, the greater the inductance of the primary coil required (the inductance is proportional to the square of the number of turns), so the impedance ratio of T in the low frequency band is higher .
Constructed by 2N3553 successfully declassified, working in category C. R1 is used to reduce the Q value of the secondary coil of T to prevent the occurrence of parasitic oscillations. But at the same time R1 will cause some power loss, especially when R1 is small. Because the lower the frequency, the higher the gain of the transistor, so the value in the low frequency band is small, which is used to offset the increase in the output power of the main vibration stage. C4, C5 and L (the capacitive or inductive reactance marked in the enclosure) together form an ∏ type output matching network with input and output impedances of 50 ohms. With QL = 10, the filtering performance is good. The output power is not greater than 1.5W, which may be slightly smaller-I will introduce a power expander circuit that can be matched with this circuit in the future.