"Mike" wrote in message
...
A ground plane has 5 to 8dB more gain than a Discone? Where do these
numbers come from? If you look at the gains and plots from any
commercial/military Discone you will see it is about on par with a 1/4 wave
groundplane across most of the Discone bandwidth. I don’t mean inflated
scanner Discone specs, look at commercial companies that reference to
isotropic or 1/2 wave dipole for measurements. At the upper end of the
Discone’s range the pattern can get a bit squirrelly, but then a ground
plane with only 3 or 4 radials does not put all of it’s energy at the
horizon either, the mail lobe is at least several deg higher than the
horizon. A “scanner” type Discone will perform within 1 or 2dB of a 1/4
wave groundplane on the VHF and UHF bands, which is the lower end of its
useable range. What does this really mean? You will probably not notice any
difference between a good quality Discone and a ground plane cut to
frequency on the VHF or UHF bands. 800 MHz would benefit from a gain type
antenna if your in a fringe area.
Mike

Most discones do not exhibit gains as high as a 1/4 wive ground plane across
a wide bandwith. They (the discone) may approach these numbers at their
best points. However the real issue here is that all ground plane antennas
are not 1/4 wave. When I quoted the 5 to 8 dB better gain possible from a
ground plane I was talking about ground planes with more gain than a 1/4
wave. A 5/8 wave would have several dB more gain. Compare a 5/8 wave
ground plane to the 'average' scanner store discone (and they are in the
same price bracket) and it is easy to get around 5 dB. Or, a colinear could
get up into some real gain compared to the discone. So, while I agree with
you that a well made discone may be fairly close to a 1/4 wave ground plane,
it is far easier to make a high gain ground plane than it is to find a well
made discone. Most three wire coned scanner discones would be lucky to get
close to an isotropic, let alone the almost 3 dB more you would get from a
half wave dipole.

The last time I looked at a well made military discone (say an AT-197/GR)
the price was several times the price of a killer colinear vertical. Of
course, if you can get one surplus it can be cheap, I have three 197's
myself.

The contention of my post was that dollar for dollar, if you are interested
in one specific frequency or narrow band, you can get more gain with a
different antenna rather than the discone. However, a well built discone
will generally be my preferred choice for anything like a scanner or
multibanded receiver if it is physically possible. A discone on 160 M may
be possible, but I can think of a couple other choices I would try first.

C