For years I have been teaching that FM reception is rubbish in mountain areas and Long Wave reception is good. I have never noticed this as clearly as in Killin in the Scottish Highlands. Like water waves, radio waves diffract around objects. You'd expect to find a calm sheltered spot behind an object (like sheltering from the rain) but if the waves are roughly the same size as the object then they will bend round the far side of the object.
All radio waves travel at the speed of light 300 000 000 metres per second.
Radio 4 FM is 94MHz. That means the wavelength is 300 000 000 000 divide 94 000 000. This means that a wave is roughly 3 metres long. Mountains are much bigger than this so the FM waves won't bend round the mountain.
Radio 4 Long Wave (LW) is 194 kHz. The wavelength is 300 000 000 divide 194 000. This means the waves are about 1500 metres long. That's much closer to the size of Ben Lawers, shown in the picture! The views from the top were magnificent. 60 miles all round. And I had good LW reception in the valley but nothing on FM. I like it when Physics does what it should.
All radio waves travel at the speed of light 300 000 000 metres per second.
Radio 4 FM is 94MHz. That means the wavelength is 300 000 000 000 divide 94 000 000. This means that a wave is roughly 3 metres long. Mountains are much bigger than this so the FM waves won't bend round the mountain.
Radio 4 Long Wave (LW) is 194 kHz. The wavelength is 300 000 000 divide 194 000. This means the waves are about 1500 metres long. That's much closer to the size of Ben Lawers, shown in the picture! The views from the top were magnificent. 60 miles all round. And I had good LW reception in the valley but nothing on FM. I like it when Physics does what it should.
