DAB is cheap enough to be used even by a small local radio station using only one transmitter, as shown before. That still doesn’t mean that this way of thinking is not valid for a larger area. It is, although the costs will of course be higher. The bottom line is that DAB will almost always be cheaper than FM.
The capital of Norway
Let me try to explain. I'll start with Oslo, Norway's capital. Between 600,000 and 700,000 people live in the center, almosta million in Greater Oslo. Three local stations here are available both via FM and via DAB+. They require one transmitter each for FM (1+1+1=3 transmitters), but only one transmitter combined for DAB+ (and this transmitter can even handle 17 additional radio stations). The coverage areas for DAB and FM are comparable.
I'll stay in Oslo a little longer. Norwegian Broadcasting Corporation (NRK) has three FM transmitters for NRK P1. There are 4 DAB transmitters, although one of them primarily covers an additional area.
How to measure coverage?
NRK P1 is the radio station that is required by the government to cover “everyone in Norway” via FM. 1,111 transmitters are needed to do so. But how many is everyone? These 1,111 transmitters cover “99.95%” of the population in mono, given that they have a receiving outdoor antenna 10 meters above ground level. Almost no one has installed such antennas, so this is not a good nor accurate nor user friendly way of measuring coverage.
The DAB 99.5% indoor coverage corresponds to the FM 99.95% outdoor 10 meters above ground level coverage, and is a better and more precise way of measuring. We may even call it future proof.
The 765 DAB transmitters broadcast from 765 sites (“towers”), and each and every transmitter transmits up to 20 radio stations. The radio stations are all the same throughout the country, but some regional content differ throughout the day on certain radio stations (made possible by using seven multiplexes – all 765 transmitters could however have been configured to one multiplex).
The 1,111 FM transmitters on 1,111 sites do transmit one radio station only, to the same amount of people. Some of the programs on NRK P1 are fed locally in order to accommodate regional content at certain times of the day.
99.5% indoor coverage
DAB+ will cover 99.5% of the population when the network is finished in 2014. And yes, we are talking about indoor coverage and a lot more roads than what FM will ever cover. 765 DAB transmitters are needed to do so. More about that here.
DAB does in other words require substantially fewer radio transmitters and sites than FM. And the electricity used for DAB is under half that of FM. The future is digital, even for radio.