23 cm PA with Mitsubishi RA18H1213G
The finished 23 cm PA.
| This page describes how I assembled a 23 cm PA kit based on the Mitsubishi RA18H1213G power module. All components except the power module were purchased from Bert Modderman PE1RKI. He is a wizard with his CNC milling machine. Mechanical parts sold by him are perfect! |
Photos
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The kit from PE1RKI.
Bottom side of PCB. The
delivered PCB did not have through-holes (through-holes connect
top side tracks to bottom side tracks). I soldered 5 wire
bridges and made the bottom side smooth using a file. As you
can see, some of the wire bridges are inferior (my fault - too
much filing). Lastly, the PCB bottom side was thoroughly
cleaned.
The PCB is fixed inside the metal house with 5 screws. I
checked the connection between the metal house and the 3 ground
connected tracks. The diode tester showed 0.00 volt, which indicates a
perfect connection with no voltage drop. Some time later, the wire bridge connecting the middle track to ground failed. I had to connect the middle track to the leftmost ground track using a short piece of wire. The PCB is not removed from the house during fitting and soldering of the remaining components.  Sanding the bottom side of the power module. To
make the bottom side of the power module smooth, I first
removed the two protrusions with a file. Then
followed sanding to further smooth out the surface. |
 Bottom side of the power module ready for fitting. The
picture shows the bottom side of the power module, which is ready
for fitting into the metal house. Both input and output wires
were soldered to the ground wires to prevent ESD during sanding.  All components are mounted. The
power module is mounted without any thermal compound. A solid RF
ground is more important than slightly improved heat transfer. The input connector (sma female) is seen to the left; the output connector (same type) is to the right. The grey feed-through carries 12 V (Vdd ) and the red one enables bias (12 V) for linear operation. The bias voltage Vgg is set with the trimpot and lies between 0.1 V and 4.9 V. The two solder lugs serve as ground connections.  The heat sink measures 200 mm x 75 mm. The
metal house is fastened to the heat sink by 4 screws in the corner. A
thin layer of "Arctic Silver 5" is applied between the metal
house and the heat sink in order to enhance heat transfer.  Height of the heat sink is 40 mm. |
 The finished PA. One or two fans are needed to cool the heat sink. Testing with 23 cm transverter. To be described later. |
Written by OZ1BXM
Lars Petersen 04-Sept-2011.