antenna power feed

hi all i would be thankful for ur help on power coupling issues in antenna (rf section ) i need to design a coil for the frequency concerned (f=1/(2pi sqr root(lc)) and feed the power to antenna. the problem comes in getting correct inductance coil designing and testing its value and secondly why the point of tapping power for antenna needs to be done at particular point on coil (i.e. like, one and half turns from positive feed) thanking you all.

A coil for what? Coupling to the antenna? If so, coupling WHAT to the antenna. Loading an antenna element? Acting as an RF choke in a ground connection? You're not exactly giving a lot of context for someone to work with, here.

Bob M.

The choice of inductance is often driven by the required Q. This may be somewhat arbitrarily chosen e.g. anywhere between Q=5 and Q=10 for a class C transistor PA stage.

A tapped coil is an auto-transformer. The tapping point controls loading. If you put the tapping in the middle, the transformation ratio is 4:1.

The dynamic impedance of the (transformed) antenna load across the whole coil, the loaded-Q and the inductance are related:

Loaded Q = R / wL

w = omega = 2*pi*f