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When I watch digital TV channels from a terrestrial transmitter, I have to endure periodic disruptions during which the audio and video start stuttering. I recently realised that the disturbances occur every time motorbikes – particularly scooters – pass my house. This doesn’t happen with cars. How do scooters disrupt my TV?

• Petrol engines use an electrically generated spark to ignite the fuel-air mixture. A modern car uses a solid-state electronic ignition system, connected to the using cables which reduce the level of electromagnetic radiation from the engine.

In contrast, many motorcycles and scooters, especially those with two-stroke engines, use magneto ignition systems. A magneto is a simple mechanical device involving a coil and a magnet that can generate a high voltage when it is needed. It is connected to the spark plugs using metal cables rather than the high-resistance cables used in cars, which are not well suited to a system. As a result, magneto systems emit much higher levels of electromagnetic radiation than electronic ignition systems.

The high-frequency component of this radiation can interfere with broadcast signals to such an extent that your receiver’s error-correcting routines cannot cope.

Stewart Haywood, The Colony, Texas, US

• This problem is worse when receiving terrestrial digital TV than with analogue transmissions. Analogue technology is far more robust and just displays such interference as white dots on the screen. However, with digital technology there is a very high level of coding in the signal waveform. The result is that ignition interference (and indeed other kinds of interference) can disrupt the decoding process in the receiver, causing the picture to stutter or even freeze completely while the decoder recovers and gets back in sync.

Sometimes replacing the aerial cable with a double or triple-screened variety can cut the amount of ignition pick-up and so reduce glitches.

Richard Harris, Malvern, Worcestershire, UK

• In the UK analogue TV transmissions are due to be switched off in 2012. Until then, digital terrestrial signals are being transmitted at reduced power to avoid interference with analogue signals. When the digital signal strength is eventually increased, the improved signal-to-noise ratio detected at the receiver should overcome this problem.

I should add that I cannot receive digital terrestrial signals at all. My neighbour can, and suffers from the same problems as your correspondent. We have identified the individual scooters, motorcycles and cars responsible – they are all rust buckets.

If it makes anyone feel better, I watch free-to-air satellite channels with a 1.2-metre dish and find that one particular motorcycle interferes with that too. This is amazing as the signals are all in the gigahertz rather than the megahertz range, and the interference is coming from outside of the line of sight to the satellite.

Adrian Frame, Norwich, Norfolk, UK