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Why some radios have to be grounded?

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Nigel Goodwin

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D.J. said:
Hi everyone,

I was curoius as to why some radio's have to be grounded while others don't?

Car radio's don't have to be grounded but when I built my coil/cap filter for my radio, it had to be grounded or it didn't work:? .

Even on little transmter and reciever schematics, they are grounded.
Conventional low frequency aerials require the receiver to be grounded, because that's how they perform far better. A car radio is actually 'grounded' to the body of the car.

A lot really depends on the frequency used, and the type of aerial - for example a ferrite rod aerial doesn't require grounding, as used in your portable MW/LW radio. An FM VHF whip aerial (as used on a car, or a portable radio) doesn't need grounding, because it's one half of a dipole aerial - the other half is a virtual rod, reflected in the bodywork of the car, or (very poorly) inside the portable radio - it's known as a'ground plane'. If you actually stand your portable FM radio on top of a car, it's performance improves greatly - as the car body acts as a proper ground plane.

As previously suggested in these forums, you might try getting hold of either the ARRL or RSGB handbooks, these are an excellent introduction to radio. You might also consider taking a course and passing your RAE?.
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