Community Radio technologists attending the Technorama conference have called on the ABC to turn down the power on some transmitters, to decrease interference to other stations.

In a presentation on transmission and interference issues, KL FM Bendigo’s Mike Tobin detailed the interference caused to his station by a triple j transmitter in Griffith, a situation echoed by several other stations at the conference. Interference issues included multi-path and third order intermodulation issues.

His point was that transmitters don’t always have to run at their full allocated power to cover their service area. In fact, it can often be more efficient to tune up a transmitter to optimum efficiency using less than maximum power. Transmission engineers at the conference estimated cost savings of 10% to 20% with the right transmission strategy. “In a time of tight budgets the ABC could probably do with saving 10% on its transmission power bills,” said Tobin.

Sometimes people equate more power with more loudness and better coverage, but it’s not as simple as that.

Good transmission is a balance between power output, transmission site efficiency and the right kind of antenna system, so just turning up the power on a transmitter is not necessarily the best way to improve coverage or increase loudness.

The discussion was in the context of community stations looking for better ways of improving their own signals and decreasing interference from other stations in the most cost effective manner.

In a time where electricity costs are increasing and green issues are more important then ever, the call for a review of transmission power by all stations is worthy of consideration. The ACMA mandates maximum power levels for stations through its licence area planning process, and does have provisions for regular reviews of LAPs. 

Interference issues such as this are not a problem with digital radio, because all stations are broadcast from a single multiplex transmitter.

(Below)  ARFC’s Gorden Smith explains the problems of an inefficient mixed polarisation transmitter system.

Transmission tower photo from Shutterstock, Gorden Smith photo from John Maizels.