The H6 Boat Tail

The H6 transmitter sends at a frequency of 144,005 MHz with an output power of 150 mW. The design and construction of this transmitter complies with the following requirements:

• small size,
• simply to reproduce,
• consists of a minimum number of parts,
• the HF coils and HF transformer need to have a simple construction,
• all parts and materials had to be readily available from the regular electronics suppliers,
• the transmitter has to comply fully with the Dutch PTT Telecom technical requirements concerning amateur transmission installations.

A preliminary design was made based on the above requirements. The transmitter consists of three stages. The first stage is an oscillator coupled to a resonance circuit which is excited via a low impedance tap ??? by the oscillator and which is set to the second harmonic (72,0025 MHz) of the oscillator crystal. The second stage amplifies the signal from the first stage and excites the resonance circuit via a centre branch. This resonance circuit is set at a frequency of 144,005 MHz. The third stage is an amplifier stage (class C), which feeds the required HF signal via a double phi-filter to the antenna. The double phi-filter has a double function; first of all, filtering out the unwanted harmonic from the antenna signal (-60 dB), and secondly modifying the difference in impedance between the stage output and the antenna input (50 W).