Professional system installers have been using modular SCFs (Single Channel Filters) for the last thirty years in MATV systems writes Richard Stallworthy from Vision. The ability to control the level of wanted channels, and to exclude unwanted signals to improve Carrier/Noise ratios is of great value. This is particularly true for larger systems, where keeping the network free from interference is critical. With more and more signals crowding the UK airwaves the need for filters becomes even more pressing.
Showing its age

But the thirty year old technology is showing its limitations today. Modular SCF is not very selective, and can accidentally overlap channels next to the one that does need attention. Damage to adjacent channels is difficult to overcome without a significant degree of work on the part of the installer, and for this the modular SCF has gained a reputation of being “difficult to work with”. There is little on-site flexibility, as factory-tuned modular SCF components must be planned and ordered in advance, leaving the installer little leeway to compensate for real-life circumstances by tweaking equipment settings on site.

Being able to tune a filter on site has long been a desire of the professional MATV installer. Although technically possible for some years now, agile SAW (Surface Acoustic Wave) filters were too expensive before recent electronic advances brought prices down to realistic levels. As you might expect, Vision is at the forefront of this development, and launches this summer the first agile, tuneable and programmable SAW filter system at a truly affordable price.

No barriers
The new Vision Superfilter knocks down barriers in channel filtering applications. Essentially, Superfilter is an analogue/DTT head-end in a box. What's more, it offers on-site channel programming, is easy to handle and is priced to make modular SCF technology obsolete.

Superfilter comes with three basic configurations - eight, eleven or fourteen channels within the same tamper-proof cabinet. Inside the single cabinet is an integrated power supply, a motherboard to house the SAW filters and a user friendly on-site programming unit.

Quick install
Set-up is quick and simple with Superfilter. There's no fiddling around with plastic trimmers, as it's all done by pressing buttons and looking at the display panel. Superfilter uses a micro-processor to control the channel settings and levels, which can be locked to prevent unauthorised tampering after the MATV professional has left site. If several head-ends are needed in the same building, a “copy-this-configuration” feature makes cloning the first installation very, very easy, cutting hours off installation time.

Technically superior
With selectivity better than -45dB in the adjacent channel, Superfilter beats the modular SCF option hands down. This means it is much easier to equalise or balance adjacent channels. The SAW filters perform so well that in a cluster of three adjacent channels, the centre channel can be removed without harming the other two channels. Since the quality of the filtering is so high, DSB (Double Side Band) modulators can be used on adjacent channels, giving better results more cost-effectively than if VSB (Vestigial Side Band) modulators were to be used. Standard set-top box modulators become super clean low cost VSB, low in noise, and can be set to adjacent channels. Now twenty or thirty digiboxes, DTT receivers or CCTV units can be put onto the same system.

SAW filters in Superfilter have a no loss loop-through input. A number of signal sources can be configured, allowing several aerials or modulators, or a combination of both, to be used with the same Superfilter. As a self contained head-end filtering and launch unit, each SAW filter is combined at the output into a 50dB gain amplifier, with 25dB of level control per channel. Any radio FM and DAB signals are combined at the output amplifier stage.

Accept no imitations
Don't confuse Superfilter with their poor relations - Cluster filters, or even programmable agile Cluster amplifiers. Cluster devices only filter groups of channels together through relatively simple technology. This does not allow single channel adjustment to equalise adjacent analogue and digital channels. These cluster devices can only adjust one group of channels in relation to another group or channels, making them very poor at rejecting interference at the edges of the filter. Superfilter's SAW filters work with totally different way to cheaper Cluster technology.

Superfilter is ideal for MATV head-ends, or digital-IRS networks, where filtering must equalise individual channels and screen unwanted signals from the network. Typically, this might be in a hotel, with viewing points spread across lots of floors, connected by thousands of metres of cabling, and often with many signal inputs. Cost-effectively setting different levels on individual channels, both digital and analogue, is why Superfilter will soon become the system of choice for MATV professionals.

Superfilter launches Summer 2004, and will be available from established Vision stockists throughout the UK.