RF Circuits

• Rectangular holes of 2.8 mm deep have been mould in the heatsink because the transistor leads have to be soldered on the printed-circuit board. Also it was necessary to make avings of 4 mm wide and 0.6 mm deep at the positions of the straps on the printed-circuit board. The transistors have been fastened with M 2.5 screws in the heatsink (see Fig.4).
• To achieve that the printed-circuit board lays tight to the heatsink also savings have been made in the heatsink on the spots of the 8 rivets through the printed-circuit board.
• For fastening the printed-circuit board on the heatsink on 7 places, holes with M 3 screwthread have been made in the top side of the heatsink, corresponding with indicated holes in the printed-circuit board.
• The two hybrid couplers also have been fastened in the heatsink with screws through the printed-circuit board. Therefore 8 holes have been made with M 2.5 screwthread, corresponding with the printed-circuit board.
• The input and output connectors have been fastened to the heatsink with M 3 screws. The mid contact of each connector makes contact with the printed-circuit board.

CONCLUSIONS
With the construction of the BLV57 amplifiers a good thermal resistance (0.2 °C/W) has been achieved by means of a forced air-cooling. Attention has been payed to a good mechanical contact between heatsink and printed circuit board and a good ground contact on the printed circuit board by means of rivets and straps at the edges and under the emitter leads.

See more : Wireless Microphone - TV Transmitter - RF TV Modulator