antenna power feed

[nav]

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.

 

[Bob Myers]

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.

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.

 

[Andrew Holme]

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.

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