[Antennas] Impedance questions...

2002年5月30日 19:36:46 -0700

I've been reading info on quarter wave antennas.... Verticals with a ground
plane bent downward around 45� has an impedance of roughly 50 Ohms, ground
planes 90� from the radiating element have an impedance of roughly 30
Ohms... My question regards mobile magnetic mounted antennas, 1/4 wave and
5/8 wave. Since the ground plane is nearly always 90� from the radiating
element on a vehicle, do these antennas operate at 30 Ohms? I've taken many
bases apart and see nothing special in changing the impedance. Another
question: Why do 99.9% of the mobile antennas come with 17' of co-ax? Is
this a magic number for something? On a 1/4 wave antenna with horizontal
ground plane, can the impedance be changed by altering the lengths of
various elements without horribly effecting the radiation pattern?
Kurt
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Ross Technologies Signals Intelligence Division
Rosetta Proving Grounds