Radio Daze 5 - MPT1327 Trunking

Many moons ago, I worked at a Telecom Service Centre. We sold cell-phones and my key area of responsibility was Fleetlink. At this time it was Telecoms trunked radio solution. It had been very problematic in it's rollout and much of the system didn't work properly yet.

It's a brilliant concept though. Somewhat akin to cellular phones, the radios are network controlled, so that instead of a companies channel lying idle for 95% of the day, the pool of radio channels are shared out with everyone, and one is assigned a spare channel when needed. In the example video below, one can see the narrow voice channels (about 2.5 kHz) and the wider data and control channels (perhaps 10 kHz at a guess)

This is on my SDR dongle using gqrx. From a purely technical perspective, it's a great program, because it illustrates very well how the Mixer can generate negative frequencies (top right) which is solved by using IQ signals. I try to explain this by somewhat floundering with GNU radio companion below in 2 parts