Gain wrote:
"I have a 10W FM transmitter set to 87.7 MHz. I also have a folded
dipole antenna and a 20 meter high mast."

Range is determined by line of sight.

Your antenna is about 66 feet high. Over smooth earth, your grazing
point, in miles, is the square root of twice the antenna height in feet,
or the sq, rt. of 132 = 11 miles. If your receiving antenna happened to
be at the same elevation and could share a grazing point, the total
distance you could reach is 22 miles.

Antenna polarization has little effect on range unless you can
cross-polarize with an interfering signal which is unlikely. Broadcast
stations in the U.S.A. use both polarizations as many listeners are in
vehicles which have better luck with vertically polarized signals. The
same conditions prevail everywhere.

Have luck and fun. Try to stay out of jail.

Best regards, Richard Harrison, KB5WZI

Cheers Rich,


Have luck and fun. Try to stay out of jail.

Best regards, Richard Harrison, KB5WZI


I can assure you it is 110% legal.

Gavin.

What would this achieve??


"Richard Harrison" wrote in message
...
Gavin wrote:
"I know normal dipole antenna radiate outwards from their ends, but I`m
bot sure about the folded version."

The propagation pattern from a dipole forms a toroid centered on the
middle of the dipole wire. Radiatiation is perpendicular too the center
of the wire. There are nulls at the ends of the wire.

Adding a wire or wires between enda of the simple dipole does nothong to
change its radiation resistance, antenna efficiency, directional
pattern, or directive gain. Drivepoint impedance increases with added
wires as total antenna current is divided among them. If two equal wires
are used in the folded dipole, its drivepoint impedance is four times
the impedance of the single wire dipole. If there are three wires, the
impedance is multiplied by nine. Impedance varies by the square of the
number of same sized wires in the folded dipole.

Best regards, Richard Harrison, KB5WZI

Gavin wrote:
"What eould this achieve?"

I suppose this relates to radiation from the dipole`s ends.

There`s not much from the ends of a dipole in free-space. Radiation from
a dipole in free-space is patterned as a doughnut symmetrically placed
around the axis at the dipole`s center.

Kraus in his 1950 edition of "Antennas" on page 133 wrote:
"The pattern is independent of phi, so that the space pattern is
doughnut-shaped, being a figure of revolution---."

Down the same page:
"However, the near-field pattern for Er, is proportional to cos theta as
indicated by Fig. 5-6b." (shows fields about the ends of the dipole)
These are mostly reactive fields which don`t radiate.

Best regards, Richard Harrison, KB5WZI