Stuart Longland wrote:
Ahh right... I had a look around, looks like Minikits[1] sell the
power modules (and even a PCB). This looks promising.

Maybe with some more searching you can find PCBs that include the tx/rx
switching, preferably with PIN diodes. That will save you a lot of
money and construction effort.
(with a bare amplifier PCB as shown on that site, you will need relays
and a circuit to drive them when transmitting, in addition to the
amplifier PCB)

The handheld can be wound right back to 50mW when running off
batteries... otherwise 0.5W. A pi network isn't hard though. That
said... I won't make the mistake I made last time -- last time I tried
making it with 5W wire wound resistors... and wondered why it didn't
work.

It is better not to rely solely on lowpower settings of the handheld,
as sooner or later you'll forget to set it to lowpower, it will drive
5W into the module, and destroy it.
So it is best to have some attenuation in front of the module, such that
it will survive accidental input of the full power of the handheld.
You can then still use lower power in normal use, so the handheld will
not run too hot. Find the maximum allowable input power for the module
and design the pi network so it will attenuate the highest output power
of the handheld sufficiently. Then calculate the nominal power to
the module (for driving it to e.g. 90% of its max output) and use the
handheld at that power level. That could be 0.5 W or so.