On Feb 11, 5:58 pm, larry d clark wrote:
given that the length of a half wave dipole is
calculated by 468 / freq in mhz when velocity factor
is 1, ie 468 / 1.9 is about 246 ft.

i'm sitting here wondering why folks with small
city lots don't use (468 / freq in mhz) * velocity factor,
to construct a much shorter antnenna, particularly on
80m & 160m?

as an example, rg59 coax typically has a velocity
factor of .66, so plugging to the formula,
468 / 1.9 is about 246 ft, * .66 is about 162 ft.

why couldn't 162 ft of rg59 be cut in two, attached
to a 50 ohm, have the remaining ends of the rg59 shorted
together, and hoisted into the air?

so what am i missing? there are no free lunches:-)

larry
kd5foy

To achieve resonance in a shorter antenna, you can increase either the
capacitance or the inductance--or both, of course. To increase the
capacitance, all you have to do is fill the universe with
polyethylene, or some similar low-loss dielectric. You don't have to
actually fill the whole universe with it; it would work to fill a
volume around the antenna. But to get the full effect, it should be a
pretty large volume, containing the electric field in the neighborhood
of the antenna. Not very practical. In coax, the electric field is
between the wires; in the dipole, it's also between the wires, but the
volume is very much larger. On the other hand, people have been
shortening resonant antennas for a long time by increasing the
inductance: thus, loading coils and "slinky" antennas. Similarly,
people make "slow" coax by making the center conductor a helix, and
thus make delay lines.

Cheers,
Tom