VK3NX
Australian Amateur Radio Station
(432 MHz PA Utilising MRF646)


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.
External Pictures
Internal Pictures
Additional Notes on construction:

  • 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 RG6
  • A 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