Ascom SE 550
The Ascom SE-550 is available in VHF-low, VHF-high and UHF versions. It was used in several PMR and PAMR (MPT-1327) networks.
Only a small modification is needed to make the unfiltered baseband signal available to the outside world. The receiver uses an MC3361 or MC3371 IC. The modification is the same.
Pin 9 of the MC3361 or M3371 contains the baseband audio
The connection to pin 9: resistor and capacitor
The unfiltered audio can be found on pin 9 of the MC3361 or MC3371 receiver IC.
Follow the next steps to make the discriminator output:
Pin 5 of the 15 pin sub-D connector
Overview of the discriminator output
There is no need to mount an additional connector in the radio for the discriminator signal. Pin 5 of the 15 pin sub-D connector at the back of the transceiver is unused (spare). It is perfectly possible to use this pin to connect the unfiltered audio from the discriminator IC.