Making a simple and reliable 23cm linear end stage is not as difficult as it seems. A relatively simple solution is offered by the Mitsubshi M57762 hybrid module.
PA is particularly suitable for FM-ATV operation, where strict criteria for linearity are not imposed as with SSB. In non-linear mode, it can provide power up to over 20W with regard to cooling. With an efficiency of around 30%, it is not easy to cool the module. It is necessary to oversize the cooler and also use a fan.
| Output power at 1.3 GHz: | 0.2 W in: 10 W out |
| 1.0 W in: 20 W out | |
| Frequency range: | 1.24-1.3 GHz |
| Average output power: | 18 W |
| Effectiveness: | approx. 30% |
| Linear area: | up to approximately 15 W power |
| Supply voltage: | max. 17 V |
| Total consumption: | 8 a |
| Max. excitation power: | 2 W |
| Max. output power: | 25 W |
| Bias on terminal 3: | 9 V |
These data are only valid at a module temperature of 25°C. Deterioration occurs at higher temperatures!
The input and output impedance of the module is 50 ohm, so no impedance matching is necessary. The parts are soldered in a "sparrow's nest" style.
Construction instructions
- tinned box, for example 72x56x20
- VK200 is a broadband choke, it can be replaced with 10 turns of thicker self-supporting wound wire - not critical
- 1nF chip capacitors are soldered between the wall of the box and the module
- exact adaptation to the previous stage and antenna is possible with trimmers
- 10uF and 15uF capacitors can be tantalum at 30V
- 1N4001 (or stronger) protects the PA from reverse polarity. There is a 6A fuse in the supply
- input and output connectors are BNC or N (not SO-239/PL!) and their frame is soldered to the box
- 5pF trimmers must be of high-quality design (SKY, etc.)
- the module must have the best thermal contact with the cooler! Don't skimp on silicone paste!
- the connection of the output from terminal 5 to the connector is made with a 50 ohm Teflon coaxial