Simple two stage one watt AM transmitter

This is a simple two-stage transistor One watt AM transmitterdesigned for the HF band. The circuit produces approximately one watt of output power. You can use easily available transistors in the final stage. Suitable transistors include BD139, SL100, 2N3866, 2N2219, or 2N3553

The 2N3553 transistor delivers approximately 1.8 watts at 12 volts. The transmitter produces more output when you modify the L1 coil. Specifically, use 7 turns instead of 4 turns in the secondary section. This coil connects the oscillator stage to the final amplifier stage.

You can modulate this transmitter for amplitude modulation using different power transformers. Experiments are necessary to find a suitable modulation transformer. The right transformer will produce good AM modulation quality.

Audio transformers from old radio receivers work well as modulation transformers. Both input and output audio transformers are suitable for this purpose. Additionally, power transformers with one amp or half amp ratings also work effectively.

The modulation transformer is crucial for proper AM operation. It couples the audio signal to the RF carrier. Proper impedance matching ensures efficient modulation. The transformer also provides isolation between audio and RF circuits.

This simple design offers good performance for amateur radio applications. The circuit uses common components that are easy to obtain. With proper construction and tuning, it provides reliable one-watt output for HF communication.

Also test with different transistors in the final stage. But be careful to not blow up the final transistor
BD139 – gives 1.2 watt output @ 12 volt
C2314 – gives 2 watt output @ 12 volt
BLY88C – gives 2.3 watt output @ 12 volt,2N2219 – gives 1.3 watt output @ 12 volt,SL100 – gives 1.1 watt output @ 12 volt

Make sure to use a power supply that can provide enough current for the transistor you are using.

Here are some additional tips for building and using this transmitter:

• Use a good quality antenna that is matched to the frequency you are transmitting on.
• Ground the transmitter chassis to a good ground.
• Keep the transmitter away from other electronic devices to avoid interference.
• Be careful not to overmodulate the transmitter, as this can cause distortion.

Please note that it is important to check the laws in your country before building or using this transmitter. In some countries, it is illegal to transmit on the shortwave band without a license.

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