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Aerial Views

From Hi-Fi World - July 2005 issue

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Aerial views

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(picture courtesy of www.mb21.co.uk)

 

Noel Keywood on everything you wanted to know about antennae…


No matter how sensitive VHF/FM tuners seem to be in their technical specification, for best sound quality they are all much alike, needing a good strong aerial signal of 1mV or more. Unless you live close to a transmitter, only an outdoor aerial can provide this, although a loft aerial may suffice. Since aerials are £25 or so, more if you live far from a transmitter and need a big array, cost isn’t great. The fitting charge will be stiffer, usually coming in at around £90 or thereabouts, depending upon difficulty. If you have a good hi-fi tuner you will find it’s worth the investment though, as a good aerial brings a wonderful sense of clarity to FM reception that’s especially noticeable with live studio broadcasts and chat shows. In this area radio can sound dramatic, having a less processed and more natural sound than you’ll hear elsewhere, even from CD.

 

Aerial technology changes little. So even today, indoor aerials remain ineffective for FM (and analogue TV). An outdoor aerial will, typically, have three elements if you live 10 miles or so from a transmitter, increasing to five elements or more at 20 miles or greater. You need a Band II array, the rods (directors and reflectors) lie horizontally. For best results the aerial should be as high as possible, free from ground and building reflections, traffic and any other source of interference. It should enjoy unobstructed line-of-site to the transmitter; if roofs are in the way an extension pole might well be needed. You can find the vhf/fm transmitter sites at www.bbc.co.uk/ reception/transmitters,  and at www.mb21.co.uk (a real enthusiast’s site). Both offer oodles of aerial advice, which I assume you can access and won’t repeat here.

 

If you have an aerial, it likely needs replacing after 10 years or so. Also, if your aerial is that old, chances are that it is analogue, not digital, and could do with upgrading. In truth there is no such thing as a digital aerial. All radio signals, like electrical signals, are analogue; digital ones just carry a digital code. As a result, ‘digital’ aerials look much like analogue ones. However, digital transmissions have been allocated different frequency bands, usually higher than analogue, making the aerials smaller. Analogue VHF/FM goes out on Band II (88MHz-108MHz) whilst DAB is transmitted on Band III (174MHz-230MHz), so the aerial is smaller. DAB is vertically polarised, to suit car and portable aerials, so the rods lie vertically.

 

Tuners like the Arcam and Cambridge raise some interesting issues. They need a Band III and Band II feed. In Central London, for example, this means a Band II FM aerial pointing SouthEast to Wrotham and a Band III for DAB pointing South to Crystal Palace or North to Alexander Palace, the two aerials being coupled (diplexed) into a single downlead. Radioscape tell me although rated as a 50ohm input, normal 75ohm aerials and downleads match their module well enough. If you run DAB alongside vhf like this, then the aerial issue gets a little complex.

 

Although DAB needs little signal, equally DAB transmissions don’t travel as well as FM, being obstructed by large buildings, basements and such like. Consequently, there are plenty of dead zones where you may not receive it. Again, try and install an aerial high up; with DAB a small, simple aerial will often do.

 

Many DAB tuners are able to receive L Band transmissions. These are not due in the UK until 2007, although L Band test transmissions are currently being made from Crystal Palace and Leicester Square, Central London. L Band is high frequency and short range and no one quite knows whether it will ever be used in Britain as there’s little perceived need. Also, by 2007 DVB-H may well have arrived, in which case DAB could well be sidelined, at least for quality broadcasting where bandwidth is needed.

 

Think of the aerial as your tuner’s front end. If you want the best sound quality, don’t ignore it. A good aerial will ensure you get fantastic sound quality from a good analogue tuner, as some of the best programme quality going comes from live VHF/FM radio.

 

 

WEBSITES:

www.tvaerials.com lists aerial manufacturers, like Antiference, Maxview, Triax, Televes, etc.

www.mb21.co.uk is an enthusiasts site with copious transmitter data, great pictures including aerial shots (see Holme Moss) and even historic data.

www.wrightsaerials.tv is another site with a superb picture gallery and lots of detailed info on cables, aerials, faults, cowboys and much else.

 

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