On 07/02/2015 17:24, Jeff wrote:

Even in the areas where the police used FM they were required to have
one AM channel for compatibility (on VHF). Some of the later police
mobiles were capable of both AM or FM on a channel by channel basis.

I did that with a Pye Cambridge AM10B in the early 80s.

145.800 AM using the original circuit, plus few simplex and R4 (GB3FF)
for FM using the Garex NBFM IF kit, with audio applied to the screen
grid of the oscillator for transmit.

I could've saved a lot of work if I'd bought a Pye Whitehall to start with.