220 MHz ACSSB trunked systems use MPT-1327
The past few days I have been listening to the 220 MHz band. Besides the 220 MHz FM system there are a number of active ACSSB frequencies here in Boston. Some of the channels appeared to be trunking control channels.
I have an AOR 8600 that will do SSB in the 220 MHz range. I was able to tune in the voice easily on LSB. There is a high frequency audio tone present on keyup that I think is used by the ACSSB radios to tune in the voice. The amplitude compandering does not affect receieve audio that much.
The audio from the control channels sounded like MPT-1327. I used the linux version of tronkito and was able to decode the control channels and some of the trunking data on the traffic channels. It appears that the "base" frequency is 219.9975 MHz with 0.005 MHz steps. I just fed the audio from the headphone jack of the 8600 into the line input of the computer. I made sure the level was not too high.
The decoding does not appear solid. I think it is due to the high frequency audio tone interfering. The next stage is to filter the tone out and see if the decoding improves.
I was able to log seven sysids (5ae9, 5af9, 5b11, 5bd9, 5be1, 5be9, and 5bf1).