|The top picture opposite is of the main beacon 1W PA
module, whilst the
lower one is of the standby 1W PA module.
Different device line-ups have been used on the two modules, but each
use three stages to amplify the 10 mW input by 20 - 21 dB up to just
over 1W. In the case of the upper (main) module, an internal output
isolator is used, whereas the standby unit relies on an in-line
The incoming supply rail at 14.5v is regulated down 9/10v and 5v - the
latter being used to power a -5v generator for supplying bias for all
the Gaas fets. Each device +ve supply rail is current limited to add
protection to the device, which are all bl****y expensive.
Adhesive backed aluminium tape is used to provide a semi-permanant lid
on all the individual housings, and relies on capacitive coupling on
the overlaps. This avoids the casting lid having any coupling effect
when fitted, and works quite well. It is also cheap...
waveguide, with one the long sides removed, is used to house the
various gaas fet amplifiers. Each device is bolted down to a piece of
1mm copper that has been soldered to the pcb groundside and garauntees
a good reliable source connection. All but one of the gaas fet have a
base to lead offset of 0.8mm, which is very convenient when using 0.8mm
pcb laminate. Teconic RF-35 material was used. Matching is
achieved using suitably placed stubs along the line.