VK3NX





Australian Amateur Radio STation



432 MHz Amplifier utilising 2 @ 2 @ mrf 646



The amplifier depicted below was based around a board layout designed by VK3BRZ (VK3PY) Carlo Gnaccarini.

Each board utilises 2 X MRF646 transistors to deliver ~100-125 W on 432 MHz. 2 of these boards were combined using a coaxial Wilkinson combiner to produce 250W PEP output. The driver stage was also designed by VK3BRZ and it utilises a single MRF646 to produce 50 W of RF, that is then split to drive each of the main boards.
An excellent full description and constructional notes can be found on the site of IT9VKY.
Numerous boards have now been reproduced predictably. Carlo and I have individually and successfully combined 2 of the boards to produce a 200-250 W PEP "desktop" amplifier for 70cm with modest cost.



Additional construction notes




5 Heatsinks were "bolted" together

Each Heatsink was 220 X 75mm

Each MRF646 sat on 1 heatsink and as such "cooling" is more than adequate without the use of forced air.

The RG6 Wilkinson combiner was changed for an "Air" Coaxial combiner in the final version due to excessive loss and heating in the RG6A

Tohtsu CX120P was used on the output

A PEP converter Wattmeter was added

With the driver board used, only 5W input is required for 250 W output



VK3NX