CW Transmitter 5 Watt

Posted on Aug 29, 2012

This is a very simple 5 watt CW TX based upon a TTL logic chip. There is just one `tricky` component and this is Cx. This component should have an impedance of about 10 - 50 ohms at the frequency of interest. If you wish to reduce the transmitter power, increase the value of Cx. It is Cx which causes the square wave from the output transistor to approximate a sine waveform. The value of Cx is the price of simplicity in this TX.

Click here to download the full size of the above Circuit.

STARTING values for Cx are as follows (but there is a LOT of leeway) 1.8 MHz = 4.7nf 3.5 MHz = 2.2nf 7.0 MHz = 1.2nf 10 MHz = 820pf 14 MHz = 560pf 18 MHz = 470pf 24 MHz = 390pf 28 MHz = 330pf It is far better to use too high a value for Cx initially then reduce it to achieve the correct RF output power. The value of Cx will depend upon your choice of TR1. Virtually any RF power transistor will work well in this application, as long as it will handle 800mA continuously. I have even used a BC108 in this application but the RF power was restricted to about 150mW. Cx was about 5x the value quoted above. The output tuned circuit uses a coil WITHOUT ferrite slug. Use the usual "rule-of-thumb" formula for the tuned circuit; Coil = Wavelength (in meters) = number of turns Capacitor = Wavelength (in meters) = Capacitance (pf) This will get you in the right area although it could differ widely with different coil formers. The coil output winding is from 5% to 15% of the total number of turns. Adjust the output winding before reducing the value of Cx. You need the least number of turns that will give you the power needed. Connect +5 volts to the SN7400 chip and +12 volts to the PA and you will have over five watts of power out. To key the TX put the key in the +12v lead. You MUST use an antenna LP-filter with this rig if you are using a good antenna. If the antenna is tuned (magnetic loop or frame antennas...

Leave Comment

characters left:

New Circuits

Zero consumption Anti-theft High power Code Switch for E-Bike Batteries

This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
Ultrasonic distance finder circuit

The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Simple Metal detector circuit with CD4030

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Fully automatic watering circuit for flower pots

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
Simple deep searching metal detector circuit

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
Sub-Harmonic Bass Converter for Electric Guitars

The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
Echo Depth Sounding Sonar for Boats

In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
100W HiFi Audio Amplifier Circuit

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
Plant-Pot Water Level Indicator Circuit

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....