1296 MHz PA 

with Mitsubishi RA18H1213G

The finished 23 cm PA.
Figure 1.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 beautiful and perfect!  

Circuit diagram

Circuit diagram
Fig. 2. Circuit Diagram.

Some component values in the kit (delivered by PE1RKI) were diffent from the circuit diagram:

ComponentCircuit DiagramDelivered with kit
C2, C5, C8, C947 nF6n5 SMD
C4, C6, C7, C1010 F22 F SMD
R1, R2, R3, R4220 ohm240 ohm SMD

Photos

Click any image to enlarge. Hit "Back" to return here.

The kit from PE1RKI.

Figure 3. Kit from PE1RKI.

Bottom side of PCB.

Figure 4. Bottom side of PCB.
The delivered PCB did not have plated-through holes (plated-through holes connect top side tracks with 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.

print layout
Figure 5. Print lay-out.

Print

Figure. 6. The PCB is fastened with 5 screws.
There was an error on the PCB. I had to cut a copper track. It is marked in the picture above. Click the picture for a better view.

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.

The PCB stays in the house during soldering of the remaining components.  

Sanding the bottom side of the power module.
Figure 7. Sanding the bottom side of the power module.
To make the bottom side of the power module smooth, I first removed the two metal protrusions with a file. Then followed sanding to further smooth out the surface.    

Bottom side of power module ready for fitting.
Figure 8. Bottom side of the power module.
The picture shows the bottom side of the power module, which is ready for fitting into the metal house. Input and output wires were soldered to ground to prevent ESD during sanding.

All components are fitted.
Figure 9. All components soldered.
The RA18H1213G module is mounted without any thermal compound. A solid RF ground is more important than slightly improved heat transfer.

I have added a short piece of wire between the cathode of D1 and the leftmost ground track. This wire is optional.

The input connector (sma female) is seen to the left; the output connector is to the right.

The grey feed-through capacitor carries Vdd and the red one enables bias (apply +12 V). The bias voltage Vgg is set with the black trimpot.  

The heat sink measures 200 mm x 75 mm.
Fig. 10. The black 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. 

The heat sink is 40 mm high.
Figure 11. The heat sink is 40 mm high.

The finished PA.
Figure 12. The finished PA (bottom side).

The 80 mm fan is attached to the heatsink.
Figure 13. The finished PA (top side).
I did not use the two small fans included with the kit. The 80 mm fan in the picture is powerfull and almost noiseless. The air is blown from above onto the heat sink and distributed between the fins.

Measuring output power


PinPoutBias CurrentTotal Current
300 mW23 W3.5 A8.2 A
400 mW23 W3.5 A8.4 A
100 mW15 W1.0 A5.2 A
200 mW20 W1.0 A6.4 A
300 mW21 W1.0 A6.7 A
100 mW5 W0.4 A2.9 A
200 mW17 W0.4 A5.2 A
300 mW19 W0.4 A5.9 A

Measurements in lab
Figure 14.
Photo from the lab during measurements. Click to enlarge.


Written by OZ1BXM Lars Petersen. Latest revision 06-Feb-2017.

Home