AS EXPLAINED last month, all the components in our new Doppler Radar Speed Gun are on two PC boards. The smaller DOPPLER1 board contains the microwave head circuitry and fits inside a small shield box attached to the underside of the coffee-can antenna barrel. By contrast, the larger DOPPLER2 board carries the counter/display unit circuitry and
fits inside a standard UB1 plastic utility box.

The two units are linked by a single cable that’s fitted with a Type A USB plug at each end.

Although the larger DOPPLER2 board has more components on it than the smaller board, it’s a little easier to assemble because it’s only single-sided and the components are all of the familiar "leaded" type. This being the case, we’re going to assemble this board first.

Counter/display board

Fig.5 shows the assembly details for the counter/display board. Begin by fitting the 12 wire links. These can all be made using tinned copper wire or resistor lead offcuts, except for the one located just below transistor Q3. This link should be made from a short length of insulated hookup wire, because it runs quite close to a lead from the 1kW resistor just below it.

Where to Buy A Kit This project was sponsored by Jaycar Electronics and they own the design copyright. Kits will be available from Jaycar stores and dealers.