Spectrum immediately above 174 MHz is used for television broadcasting, and below 174 MHz mainly for land mobile purposes.
The introduction of Digital Terrestrial Television Broadcasting (DTTB) in the year 2001 in metropolitan areas, and by 2004 in regional areas of Australia has potential implications for users of the VHF high band. Emissions from DTTB transmissions on VHF TV channel 6 (174 - 180 MHz) could cause interference to receivers in the VHF high band (148 - 174 MHz) in some locations.
In April 2000 the former ACA completed an initial technical study that scoped the interference risk from VHF channel 6 DTTB transmissions to the land mobile radio service (LMRS) operating in the upper part of the VHF high band. This report describes a methodology, and used the DTTB emission characteristics available at the time, to estimate interference potential for the LMRS.
As DTTB trials progressed, more detailed measurements of DTTB emissions were made. Using this new data the interference estimates made in the initial technical study were refined. A copy of the technical study and refined interference estimates (PDF 367 kb) is available.
In October 2000, the former ACA gave potentially affected licensees advance notice of possible interference to some VHF radiocommunications systems operating in the band 168-174 MHz. A chart depicting the zone of potential interference (PDF 20 kb) was also provided to these licensees.
Spectrum Embargo 32 was also introduced to inhibit assignments for new fixed or mobile services in the frequency band 168 -174 MHz about DTTB Channel 6 transmission sites. Locations of DTTB channel 6 sites are also listed in Embargo 32. Embargo 32 is updated as the ACMA releases new digital channel plans.