DAB+ Canberra | FM DXing

Tropospheric digital reception

July 7, 2012 by fmdxing 2 Comments

Digital broadcasting systems such as DAB-T radio & DVB-T television can enable an enthusiast or free-to-air consumer to receive high definition 1080p digital video broadcasts and multiple channels without signal degradation such as noisy ‘snowy’ video. (From a consumer’s perspective, it is not insignificant that Wimbledon & the AFL are sometimes only shown on the digital video subchannels which perhaps forces viewers’ attention to maximizing DVB-T reception rather than reliance on the more robust ‘limited edition’ analogue signals).

On the downside, the digital broadcast signals are more fragile (e.g. pixelation & ‘borderline’ decodes can be problematic). The DVB & DAB+ transmitters utilize sharply directional antenna arrays so the crude ‘point-and-shoot’ approach to reception needs refinement. Moreover, in this region, the digital broadcasts are not designed to cover the original analogue reception from the same major site (such as Mount Tamborine). Instead, multiple sites in this region employ Single Frequency Networks (SFN) to provide a backup for those consumers who are in a black spot and cannot get reliable reception from the main site.

The analogue television switch off has meant that a digital signal meter (previously solely the domain of the professional installer) is sometimes necessary. In past, pointing the antenna to the azimuth where the analogue signal was of the highest S/N ratio, the DVB-T signal was often also peaking where the broadcast was from the same site. This is an oversimplification, and assumes the digital (DVB) and analogue (PAL B) share similar transmission parameters. Significant factors such as co-channel interference off the back of the receiving antenna may also come into play.

It cannot be denied that the challenge is considerable. However, there is a wealth of information available to the public. A considerable number of enthusiasts are ‘playing’ with fortuitous & DX DVB-T television, perhaps even more than analogue radio enthusiasts. The rewards are worth it! Thanks to the enthusiastic advice of Ian, Jamie & Leigh VK2KRR, this blog is now able to cover DVB-T reception… stay tuned. With the efforts of the Mobile Muzza in receiving the DAB+ Canberra multiplex from Goulburn it is clear there is some good company to be shared.

The photographs on this blog entry comprise two of the largest antennas suitable for long distance UHF DVB-T & VHF DAB-T reception. By no means are these necessary, these are merely a sample of the extensive range of antennas commercially available for this pursuit.