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GPS-Based Frequency Reference; PT.2

Last month, we published the circuit for our new GPS-Based Frequency Reference and described how it works. This month, we show you how to build and adjust it.

By Jim Rowe

Building the GPS-Based Frequency Reference is quite straightforward, since all the parts are mounted on two PC boards: a main board coded 04103071 (143 x 123mm) and a smaller display board coded 04103072 (145 x 58mm). All wiring between the two boards is via a short 16-way ribbon cable, fitted with an IDC line socket at each end (to link CON6 & CON9).

Everything fits snugly inside an ABS plastic instrument case measuring 158 x 155 x 65mm, the display board mounting vertically at the front. As you can see from the diagrams and photos, the main board has a small rectangular extension at front right for the 10MHz and 1MHz output connectors (CON1 and CON2), while the display board has a matching rectangular cutout to fit around these connectors.

In addition, the display board has a small cutout at upper left, to provide clearance for the interconnecting cable between the two boards.

When the case is assembled, output connectors CON1 and CON2 are accessible via the front panel, while the remaining connectors are all accessible via the rear panel. The LCD and status LEDs are also at the front, along with the three main control pushbutton switches (S1-S3). The GPS receiver initialisation button (S4) is operated via a small access hole in the front panel, along with a similar access hole for adjusting the display contrast (via trimpot VR2).

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