: There are many types of conical antennas, the discone being an example of
: a very efficient broadband conical vertical. As you correcty point out,
: a discone has the disk at the top! Several manufacturers, such as TCI
: and Granger sell cone antennas that may match the brief description you
: provided. Their theory of operation differs from the discone, and they
: are probably somewhat less efficient.
: 73!
: Frank
: W3LPL
: donovanf@sgate.com
: On 27 Aug 1995 Gary_Jacek@Cyberstore.NET wrote:
: > Hi
: >
: > I recently drove past a building in town with what looks like a discone on
: > the roof. It appears to be mounted upside down. The 'disk' being at the
: > bottom and the open end of the cone at the top.
: >
: > I'm just curious whether this has any effect on performance.
: >
: > ..Gary
A discone antenna makes a good all around scanner antenna. The FAA has used discones at airports for
many years. One discone will cover 118 to 136 Mhz and 200 to 350 MHz and have a fairly low VSWR.
As you go up in frequency the relative size verses the wavelength becomes larger and you get higher
gain but the radiation angle also goes up. "Radiation Angle" is the angle above the horizon where
the antenna has the highest gain. For most scanning the signals are on the horizon so you want a
radiation angle at zero degrees, ie parallel with the horizon. A discone at low frequencies has an angle just above the horizon as you go up in frequency
discone upside down you will have the greatest gain below the horizon for better penetration
