Topband: 1/4, 1/2 or 5/8 vertical summery

[Tom Rauch]

> I would have thought that the 1/2 wave vertical would have
come in first with the lack of a good ground radial system I
alway thought the 1/4 wave and 5/8 wave performance was very
dependent on the radial system.

Rich,

Any vertical is ground dependent, although some more than
others. The 5/8th is an automatic no sale. Even the AM
broadcasters learned they are no good and quickly quit using
them.

A half wave spreads the fields around and does reduce loss
considerably when you don't have a ground system. I disagree
that feeding it is difficult, but it certainly isn't as easy
as with a 1/4 wl or 3/8th wave.

You need a matching circuit that matches maybe 4000 ohms to
50 ohms. With a normal L/C network that roughly requires a Q
of the square root of the impedance ratio, or sqrt of 80
around Q=9. The cap would then have about 4000/9 or about
450 ohms reactance. That's about 200pF.

At 1500W with a typical air wound good construction coil
(silver plate is meaningless) you have:

3500 volts peak on the cap
5.4 amperes RMS through the cap and coil
43 watts of heat in a coil with a Q of 300
97% power transfer, 3% heat.
.6 amperes flowing to ground at the network.

You should be able to move about 25kHz or so. This does not
include antenna losses. So you see, it is workable if you
have a 4.5kV 400pF variable cap and a 40uH or so inductor
that can handle 3.5kV at 5.5 amperes.

You have to decide if building that network is cheaper and
easier than laying down 50 1/4 wl radials, because either
way your signal will be the same. There is no free lunch.

73 Tom