Foreign interference on FM radio

Occasionally during summer, distant stations you wouldn't normal be able to receive can suddenly be heard on your FM radio. The interference can last from a few seconds to many minutes - perhaps even over an hour. The station you hear may change and the signal may be strong enough to cover your normal station reception. The cause is a short-lived atmospheric effect known as Sporadic-E (Es). This allows VHF signals to be received strongly over hundreds of km, including those on the FM broadcast band. Though Es can occur in the winter it is most prevalent during June, July and early August.

A gentler form of foreign interference occurs during stable, fine weather caused by high pressure.  It is known as tropospheric propagation.  The foreign station can fade gradually in and out over several days, and is usually the same station each time. It may be accompanied by whistles. TV reception can sometimes be disrupted as well.  


What to do

Both of these types of disruption are due to changes in the atmosphere and nothing can be done to prevent them. Fortunately they are normally fairly short-lived. Reception via satellite and online remains unaffected by these problems.


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