# antenna power feed

Discussion in 'Electronic Basics' started by nav, Mar 3, 2006.

1. ### navGuest

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.

nav, Mar 3, 2006

2. ### Bob MyersGuest

"nav" <> wrote in message
news:...
> 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
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.

Bob Myers, Mar 3, 2006

3. ### Andrew HolmeGuest

"nav" <> wrote in message
news:...
> 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.

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

Andrew Holme, Mar 3, 2006