If reception is a bit hissy, the signal is weak. If you are using a portable or a Hi-Fi with a wire aerial, adjust the position and angle of the aerial to get the best signal. Sometimes, reception is better near a window. If this does not give a good stereo signal, install a roof or loft aerial or switch to mono.
If reception is weak with a roof or loft aerial, a number of things can be done to improve it:
1) Replace a circular non-directional aerial with a directional aerial;
2) Check that a directional aerial is pointing at the correct transmitter (grid references are given in the Frequency order section;
3) Move a loft aerial to the roof;
4) Install a radio frequency amplifier at the aerial.
The aerial elements should be set horizontal where the transmitter power exceeds 0.1 kW.
If reception is distorted, multipath interference maybe a problem. The only solution to this is directional reception. Setting a simple wire or rod aerial horizontally may do the trick. Otherwise, a directional roof or loft aerial will be needed.
If you want to listen to a weak station and a stronger station on a nearby frequency is causing interference, altering the aerial may help. Another option is to tune your radio 0.05 or 0.1 MHz away from the desired station in the opposite direction to the interfering station.
In cars, there is no opportunity to move the aerial. Instead, the radio automatically switches to mono and filters out high frequencies when the signal is weak in order to eliminate background hiss.
Portable radios have an internal AM aerial with the sensitive direction usually from the front and back of the radio. Hi-Fi tuners usually have the AM aerial mounted on a pivot at the back, allowing the direction to be changed; the aerial points in the direction it is least sensitive to. Rotate the radio/aerial to get the best signal.
Where there is co-channel interference, rotate the radio/aerial to minimise the strength of the unwanted signal. On the national stations, you may get interference from other transmitters carrying the same programme, particularly at night. This manifests as constantly changing fading and distortion as the phase difference changes. Again, rotate the radio/aerial to minimise the unwanted signal. This won't always work as, in some cases, the two signals will come from the same or from diametrically opposite directions, or there may be three signals. 5 Live and Talk Sport desynchronise their transmitters at night. This eliminates the fading and distortion, unless you are a long way from the transmitter. You get an echo instead, but at least the presenters are intelligible.
In cars, AM reception is poorer in some places because the aerial is omni-directional, so interfering signals can not be eliminated.
Unlike FM and AM, DAB sound does not gradually degrade as the signal declines. Essentailly DAB works or it doesn't, with marginal reception manifesting as a 'bubbling mud' sound. This makes it difficult to adjust the aerial to optimise reception. To resolve this problem, DAB radios come with a signal strength meter. The radio can be set to a particular channel and the signal strength meter used to adjust the aerial. DAB transmissions are vertically polarised, so the aerial should always be vertical. If there is insufficient signal for indoor reception, DAB will sometimes work with a loft or roof aerial. To determine if this is likely to work, first test reception outside. An external DAB aerial must be a specifically designed VHF band III aerial with the elements mounted vertically. An FM radio or UHF TV aerial will not work. Some amplified indoor TV aerials will also work for DAB as most countries transmit TV in VHF band III. These aerials will have separate telescopic rods and the packaging will explicitly state that they are suitable for VHF. They may be used where reception is possible on a window sill, but it is not convenient to place the radio there.
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