In the mid-1990s, I received an unusual assignment from the Australian Broadcasting Corporation. They had a short-wave station in Western Australia, which repeated the local radio program from Perth, the capital of that state. Western Australia is huge - bigger than most countries of the world: it's about 2000 kilometres square - but much of it is near-desert, and uninhabited. The population of the state is about 1.5 million, and almost 90% of those live either in Perth, or the coastal areas in the south-west of the state. Most of the rest live in 20 or 30 small towns, all of which have an FM repeater station. Less than 10,000 people lived out of range of an AM medium-wave or FM station.
The short-wave station was intended for people living in remote areas. But most listeners hate listening to short wave radio, and will do it only if there's nothing better. The same program had been broadcast on satellite for at least 5 years, and though satellite receivers are expensive, many people in remote areas of W.A. had bought them.
Our assignment was to find out how many people were still listening to the shortwave service.
Given the tiny, scattered population, we figured that many of them might know each other. Some of them lived on large farms ("stations" as they call them in that part of the world), and others in aboriginal communities. Using a CD-ROM of all published phone numbers in Australia, we found less than 1,000 in these remote areas.
We decided to use a snowball sampling system: to ask each respondent if they could name any others who were out of reach of normal radio. We had maps showing signal strength, but didn't completely believe them. Officially, if the AM signal strength is less than 0.5 millivolts per metre, it's not usable. In fact, we found people listening to AM with far lower signal strengths than this. Visiting some "stations" we heard AM radio that, to us, was unintelligible. But people who'd been listening to it for years could understand it quite well during the daytime. At night, there was so much interference that listening was impossible; the best signal was often soon after dawn.
We found almost nobody who listened to the shortwave service, and many people who complained of poor AM signals didn't even know the shortwave service existed - even though it had been around for decades.
On the basis of the surprisingly large AM audience, and the high percentage of outback people with satellite receivers (about $5,000 each) we saw no reason why the short wave service shouldn't be closed down. When the transmitters were built, around 1945, they were on the outskirts of Perth. By 1995, they were in the middle of a suburban area, and the land had become very valuable.
Eventually, the shortwave transmitter was closed down. Complaints flooded in, from people we hadn't found in our survey: crews of ships in the Indian Ocean, and mining and prospecting workers with short-wave radios in their 4-wheel-drives. Even if we'd known those listeners existed, we couldn't have selected them with our sampling frame of Western Australian phone numbers.
The transmitters weren't opened up again - there was too much money at stake for that. But this experience taught us not to underestimate the mobile listeners. How to find them - given that many had their homes in Perth - was quite another matter.