Hal Rosser wrote:
interesting.
if coating the antenna with ferrite can reduce its size,
would ferrite sleeves over the ferrite sleeves reduce the size even further?
we're always looking for ways of reducing the size of our dipoles.

"Tom Donaly" wrote in message
m...

Reg Edwards wrote:

Let's start a parallel thread on the effect of coating a 14-gauge
antenna wire with a thick layer of ferrite. Say 1mm thick,
permeability = 100.

Would this have any effect on velocity factor? If so, by how much?
----
Reg



In his book _Ferromagnetic Core Design & Application Handbook_
Doug DeMaw claimed to have put ferrite sleeves on a vhf dipole
which reduced its size without introducing significant loss.
He claimed to have cut the size of the dipole in half.
You'll have to do the same thing yourself if you want to know
whether or not he was right.
73,
Tom Donaly, KA6RUH




Balanis, in his book _Antenna Theory, Analysis and Design_, has
a short section dealing with this. Define a parameter
Q = (mu - 1)ln(b/a), where mu is complex permeability of
the ferrite, a is the radius of the conducting wire, and b is
the radius of the conducting wire plus the ferrite. According to
Balanis, increasing the real part of Q "a. increases the peak input
admittance b. increases the electrical length (lowers the resonant
frequency c. narrows the bandwidth." In order to use this formula,
you have to know the complex permeability of the ferrite coating.
I don't know how you'd measure that. Maybe Richard Clark knows.
It would be fun to try. I wouldn't pin any hopes on it being
practical, though, since it doesn't seem to be in general use anywhere.
73,
Tom Donaly, KA6RUH