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Radio Reception VHF/FM RADIO

The FM radio band consists of frequencies between 87.5-108 MHz and is sometimes referred to as VHF. Good quality stereo reception can be achieved normally by installing an external FM radio aerial. However reception can be impaired by the following problems.

PROBLEM >

Reflected signals

Experienced as distortion especially heard on 's' and 'z' sounds known as sibilance other sounds can also be effected depending on the severity. The problem is caused from signals being reflected from buildings, hills, cranes, scaffolding etc: which arrive at the aerial just after the direct received signal. These delayed signals interfere with the direct signal producing distortion.

What can be done?

  • Install an external directional FM radio aerial fitted with a balun to a suitable position. If possible site the aerial to a position where it can be screened from any possible offending obstacles that will cause reflections. .

PROBLEM >

Weak signals

Weak signals will cause your radio to hiss and subsequently not lock onto stereo.

What can be done?

  • Check all connections to ensure they are making good contact and that they are not shorting out.

  • Install a 75 ohm to 300 ohm balun transformer if the radio only has a connection for a 300 ohm feeder cable.

  • Install a higher gain FM radio aerial or amplifier to increase the signal either may also be necessary to compensate for weak signals caused from long cable runs or additional points split from the aerial.

PROBLEM >

Overloading

Overloading is caused from receiving too strong a signal and is experienced as a twittering sound heard in the background of the channel. It is often apparent if the aerial is sited to a high location, or within close proximity of a FM radio transmitter or when a distribution amplifier is in use and is incorrectly set. Certain radios display a calibrated signal reading to monitor the signal strength, to ensure quality reception the desired signal level for FM radio should measure between 54-74 dB(V micro-volts.

What can be done?

  • Install an aerial attenuator of the correct value. They come in a range of values 3,6, 9,10,12,18,24 and 36dB as well as variable ones.

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