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Digital v Analogue continued


We may also wish to introduce the male/female split we had in the original analogue radio setup. FDMA and TDMA give multiple access, so we could put half the radios on one setting and the others on another. Two separate systems using just one radio channel. DMR, using time slots has a problem. While they chop up their output into slots, packets of data from one radio can overlap the packets from another – so if two people use the radio at the same time, instead of the common analogue interference, that at least lets people know something went wrong, in a digital system, the radios will stay silent. A dPMR solution could be better in this circumstance.

Digital advantages

In larger systems digital can offer many real benefits. Many radios have displays, similar to mobile phones, and can show users who is calling, and store this information for inspection later. Text messages can be sent, and in large systems it’s also possible to set up zones, and groups. These features are rarely explained in any detail, and are often confusing for newcomers.


In most cases, a zone is the area covered by one transmitter on it’s own frequency. A business could have a head office and two warehouses, perhaps within a few miles of each other. This becomes 3 zones, with each one having it’s own aerial system to cover just the working area.


In the example above of the business with three separate locations, groups could be set up that cover broadly the staff structure. Sales, service, stores, cleaners etc. Each group have different needs, and requirements. The cleaner’s radios may normally be set to the cleaners group – virtually all their traffic will be to the same people, but supervisors may be swapping groups all day. In most systems it is also possible to have an ‘all’ call where one radio transmits to every radio that is turned on. Equally, individual calls can be made to other radios. Programming is everything!

TDMA Problems.

Packet collision is a problem with these systems in radio to radio use. Using a digital repeater solves many of them. Repeaters in the analogue radio world serve a number of uses. They often have aerials high up, and can re-broadcast anything received in their service area. Two low power radios can communicate through the repeater and link people who could not communicate direct. The essential feature of a repeater is to be able to receive at the same time as transmit. Digital TDMA repeaters do not just pass through the digital data stream, they process it, making sure that both time slots are timed accurately on the output. This means the portable radios have a stable timing source, which the portable radios can use to synchronise their time slots. This helps reduce the chances of time slots overlapping. There have been a few reports of some radios having less than perfect timing, and this can impact on other users trying to use the system.

For large systems the various types of TDMA protocol have made it the preferred system. Indeed, the large worldwide amateur network of local interconnected nodes means a user in the UK can have a conversation with a user in another country. Very sophisticated and useful. In smaller systems without the need for complexity and facilities, digital may not always be better?

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