Most FM tuners and mini/midi systems have an input at the back for an FM aerial yet - despite the fact that few people would be content with an indoor aerial for TV reception - most people (even radio enthusiasts) seem content to either jam a piece of wire in the socket or use a cheap "rabbits ears" type aerial stuck down behind the tuner. Many (particularly National) broadcasters seem to encourage this practice by sticking large numbers of high power relays on all over the place ostensibly to fill in reception blackspots but in practice so that they can be heard even on cruddy insensitive radios.

The most obvious one is greater choice. You’ll be able to hear all those weaker stations (pirate and legal) and in many parts of the country some cross-border or cross-channel stations as well, with a lot less interference from computers etc or fading as you walk around the room. Plus, when there’s nothing worth listening to on your local station you’ll be able (in most places) to hear stations from neighbouring counties with reasonable reception

Another benefit of an outdoor aerial (particularly a directional multielement type) is freedom from multipath interference. Multipath affects higher audio frequencies and is particularly noticeable when listening in stereo. It manifests itself as a swishing noise and in severe cases causes increased distortion (something akin to what you hear when your radio isn’t tuned in to the station exactly). Often when people hear multipath effects they blame it on a lack of signal strength and look for another station but, in fact, multipath can cause noise, distortion and poor stereo separation on even the strongest stations. Ironically the more expensive your radio the more noticeable multipath interference becomes. What sounds fine on a cheap mono kitchen portable can be unlistenable on a stereo HiFi separate tuner (switching to mono can help but this rather defeats the purpose)


As its name suggests multipath is caused by signals reaching your aerial by more than one path. The main path directly from the stations transmitter to your aerial and one or more secondary paths through the signal bouncing off objects such as hills, buildings, trees, vehicles, cranes etc (and with an indoor aerial internal walls, metalwork and even people). Multipath signals are often almost as strong as the main signal but arrive at your aerial slightly later than the main signal. While this in itself doesn’t cause any problem, timing and phase differences can result in some frequency components of the FM signal being strengthened (pre-emphasised) and others weakened (de-emphasised). The resultant non-linearity causes increased noise and distortion which affects the higher audio frequencies including stereo and (where applicable) SCA subcarriers particularly badly

1) By being outdoors the aerial is not going to be affected by reflected signals from objects inside your house.
2) As it will (usually) be mounted fairly high up, reflections from nearby objects on the ground (e.g. vehicles) won't reach the aerial or, if they do, will be arriving at an angle off the main lobe and will therefore be attenuated somewhat.
3) By having a clearer, less obstructed line of sight to the transmitter, the main signal should now be stronger than the reflected signals and so the signal should not be as badly affected by multipath.
4) Many outdoor aerials are of the directional (multielement) type and by virtue of their enhanced sensitivity in the direction of the wanted station, multipath signals from other directions won't affect reception as much, although even a non-directional (omnidirectional) dipole will have some benefits over an indoor aerial
Even a small reduction (3-5dB) in multipath signal results in bringing major benefits to audio quality due to a phenomenon in FM tuners known as "capture effect" whereby signals that are weaker than the wanted signal are (almost) completely ignored by the receiver

A topic which still causes lot of confusion when discussing aerials is polarisation - whether aerials should be mounted horizontally or vertically.
In the early days (1950s) of FM radio it was found that when the signal was transmitted with horizontal polarisation it seemed to be much less severely affected by vehicle ignition interference. Those were the days when there were very few portable, or in-car, receivers so nobody ever bothered dealing with the problem of ignition interference at source.
However by the 1970s, with transistors having almost completely replaced valves and radios appearing in cars, vehicle manufacturers started paying attention to the problem of engine interference (no point having a car radio if all you can hear is the noise off the spark plugs) and most radio listening was now being done on portable radios with small telescopic aerials which 'pointed up the way' (i.e. vertically).
Suddenly Horizontal polarisation didn’t make much sense anymore and broadcasters started reverting to either mixed (Horizontal and Vertical), or pure vertically, polarised signals. Nevertheless, old habits die hard and many aerial installers and even manufacturers still insist that FM aerials should be mounted horizontally (the fact that most TV transmitters use horizontal polorisation adds to the confusion).
In a very small number of cases (where a station one wants to hear is using mixed polorisation and there is interference from one using vertical polorisation) it makes sense to use a horizontally mounted aerial but, 99% of the time, aerials should be mounted vertically.

Two factors have to be taken into account when choosing coaxial cable - namely loss (attenuation) and screening.
Many of the cheap cables sold in hardware shops have very poor screening. This means that signal leaks out and they can also pick up lots of electrical noise and computer interference. Worst of all in this regard is that cheap white flexible stuff that you see cheap flyleads and extension leads made from. At VHF frequencies loss (measured in dB per metre) usually isn't too much of a problem unless you're diplexing UHF TV signals into the same downlead (which is perfectly acceptable provided the cable is in good condition and good quality diplexers are used at each end) or using a very long run of cable (which you should try and avoid if possible).

Try and avoid kinks and sharp bends in cables.
If you are running lengths of cable outdoors put clips or fasteners (although not TOO tight) on at regular intervals. If a cable is allowed to flop around loose in the wind eventually water will get in and destroy it
Try and minimise splits and joins on cables but, where this is unavoidable, always use good quality connectors and accessories (especially on outdoor sections of cable) and (although it might seem to be stating the obvious) any fittings devices connections made outdoors must be weatherproof
Never allow water to seep into coaxial cable. Even the smallest amount of water will make its way through the whole length of the cable causing corrosion and massive signal leakage.

A "Halo" or "circular folded dipole" (Horizontally polarised omnidirectional) aerial

First off, avoid those "halo" circular type aerials (left). They're horizontally polorised and, while they're still better than an indoor aerial, a vertical dipole (right) will give better results for less money.

A (Vertically polarised) dipole aerial (Antiference "Radio Rod")

TV aerials (especially UHF types) tend to perform poorly at FM frequencies. VHF TV aerials are a little better but what you really want is an aerial designed for FM (VHF band 2) radio (in most parts of the world Bands 1, 3, 4 and 5 are used for TV and Band 2 for radio in case you're wondering). For most people a single element vertical dipole (such as the antiference "radio rod") is an ideal choice being cheap (about £15,) easy to install (well within the capability of most DIY'ers who have access to a ladder), and are omnidirectional (will pick up stations equally well from all directions). Those wanting something a little better might go for a 2 (H or X type) or 3 element yagi which will offer a little more gain and multipath rejection for one's favourite stations while still retaining the ability to receive signals from other directions pretty well.
In weak signal areas, where all the stations you want to hear are coming from approximately the same direction, you might want to stretch to a larger aerial of between 4 and 9 elements. If you are interested in stations from several directions and have plenty of money you can invest in a device called a rotator although finding someone who can install such an aerial system can be difficult). But if you are seeking the ultimate (and have unlimited financial reserves and plenty of space and tolerant neighbours ) you can go for a massive 18-32 element system.


Ideally, it should but in practice, if roof access is a problem you can mount it high on an outside wall (you can get special brackets for this) or in an attic. Incidently if you like experimentation or are just cheap you can try using homemade dipoles in your attic space and still get far better results than what you’d get with an indoor aerial.

If you live anywhere within 15 miles of a transmitter (and if you live in a large city you probably do) the answer is probably no. What usually happens is that strong signals overload the booster and, either by themselves or mixed with other signals, appear on strange frequencies all over the FM band interfering with weaker stations - which rather defeats the purpose. Also, if you’re using a booster to make up for a poor aerial, you’re probably just amplifying signals that are riddled with multipath distortion in the first place. The foregoing also applies to those "amplified indoor aerials" one sees in shops as well. If you absolutely cannot put up an outside aerial (say you live in a ground floor bedsit or something) then there’s no harm trying but don’t expect miracles from one of these things. Incidentally, if an outdoor aerial is totally out of the question at the very least try and mount your indoor one as high as possible and near a window, but away from anything which might cause electrical interference. Booster amps can also be badly affected by two way radios and strong TV signals (low-pitched rough buzzing noise) breaking through onto the FM frequencies. On the other hand if you already have a good FM aerial but live in a weak signal area, a good quality booster can help bring in extra stations.

In some cities, and larger towns, the cable TV network carries FM radio signals as well (although on smaller networks the FM service may be non-existent or of poor quality). If you are happy with the range of stations carried, you can connect your FM radio up to the cable socket and not bother with an aerial at all. However, in many cases you’ll find the cable network doesn’t carry all the FM services in your area.
On the other hand, some services available on cable won't be receivable on your aerial. The solution to this is a device known as an aerial switch (sometimes called a "game switch" or an "A/B switch") which consists of three or more aerial sockets and a switch enabling you to enjoy the best of both worlds.

Most FM receivers have a 73ohm "belling lee" type coaxial aerial socket (left) - like the type one sees on most European TV sets, although on some radios it is a male rather than a female type socket which requires the use of a coupler (also known as a "back to back adaptor").
Some however use 'F' type connectors (the type seen on Satellite TV receivers) which supposedly give a better connection but can be awakward to connect. However you can get adaptors to match belling lee to F type connections.
Some Japanese and American equipment uses 300 ohm balanced "ribbon" type connectors which require a matching transformer - often called a "balun" (right) - and a short length of 300 ohm ribbon cable to match it to 73 ohm ribbon cable.

Ok that’s it. Hopefully this article will encourage to try and improve your aerial setup and remember you can make quite big improvements without spending a lot of money, especially if you can do most/all of the work yourself.


Finally here's some links to sources of further information and some equipment suppliers that may be useful. And no neither myself, or Radiowaves.FM, have any financial interest in any of these companies.

bbc.co.uk/reception/factsheets/docs/fm_aerials.pdf
bbc.co.uk/reception/factsheets/docs/fm_radio.pdf
wnku.org/reception/fmtips.html
fanfare.com/rfms-bk.html
weru.org/reception.html

antiference.co.uk
blake-aerials.co.uk
hirschmann.de
maxview.ltd.uk
televes.com
triax.dk

anas.worldonline.es/ronsmith/main.htm
aerial-techniques.com
taylorbros.co.uk
maplin.co.uk
cpc.co.uk

©Radiowaves.FM
©Mike from Choice FM (Mayo) 2003