Southern Avionics Company SD100 Manual Do Utilizador
SD SERIES TRANSMITTER
115
•
•
•
•
•
•
SOUTHERN AVIONICS COMPANY
SECTION 5
5 ANTENNAS:
The range of a beacon and antenna depends on many variables and cannot be guaranteed. The
field strength can be calculated if the ground conductivity is known, but the field strength needed
depends on the background environmental noise which depends on location. A field strength of
70V/m is generally adequate in the United States and Europe but may not be sufficient in latitudes
between 30N and 30S. Range figures given in the following sections are based on average ground
conductivity and a field strength of 70V/m.
field strength can be calculated if the ground conductivity is known, but the field strength needed
depends on the background environmental noise which depends on location. A field strength of
70V/m is generally adequate in the United States and Europe but may not be sufficient in latitudes
between 30N and 30S. Range figures given in the following sections are based on average ground
conductivity and a field strength of 70V/m.
The resistance of the antenna is dependent on many conditions over which the manufacturer has
no control. The ground condition, for example, is extremely important. In a high conductivity
ground region, the resistance will be fairly low. This is especially true on offshore oil rigs where
the ground system consists of a large metal structure over salt water. On the other hand, if the
ground conductivity is low, the resistance can become quite large. For example, permafrost in
Alaska generally makes a very poor ground and in most cases a special counterpoise system must
be used. Without a special counterpoise system, the antenna resistance may be as high as 50
ohms and the antenna efficiency will be very low.
no control. The ground condition, for example, is extremely important. In a high conductivity
ground region, the resistance will be fairly low. This is especially true on offshore oil rigs where
the ground system consists of a large metal structure over salt water. On the other hand, if the
ground conductivity is low, the resistance can become quite large. For example, permafrost in
Alaska generally makes a very poor ground and in most cases a special counterpoise system must
be used. Without a special counterpoise system, the antenna resistance may be as high as 50
ohms and the antenna efficiency will be very low.
THE MAST ANTENNA, "H" ANTENNA, AND 50-FOOT GUYED MAST ANTENNA ARE
HIGH Q, NARROW BANDWIDTH ANTENNAS. THEY SHOULD NOT BE USED FOR
VOICE MODULATION. THE SYMMETRICAL "T" ANTENNA IS THE ONLY ANTENNA
RECOMMENDED FOR VOICE MODUATION.
HIGH Q, NARROW BANDWIDTH ANTENNAS. THEY SHOULD NOT BE USED FOR
VOICE MODULATION. THE SYMMETRICAL "T" ANTENNA IS THE ONLY ANTENNA
RECOMMENDED FOR VOICE MODUATION.
5.1 Mast Antenna
The Mast Antenna is a short vertical monopole with capacitive top loading and inductive center
loading. It was designed for use where space is severely limited such as on offshore structures. It
is centerloaded to be resonant at approximately 500 KHz for operation between l90 and 415 KHz
and at approximately 900 KHz for operation between 415 and 625 KHz. Tuning below the reso-
nant frequency is accomplished with the antenna coupler. There are two versions of this antenna;
one designed to be mounted on land, the other on drilling platforms or ships. Neither antenna
requires guying. A capacitive hat at the top of the 34-foot Mast Antenna consists of six 8-foot
radials. These can be shortened if necessary for clearance on drilling platforms. The counter-
poise system used for land installations consists of sixteen 60-foot radials made of #10 copper
wire with 6-foot ground rods at each end and one in the center. The offshore version of the Mast
Antenna uses the platform structure and the water for the ground system.
loading. It was designed for use where space is severely limited such as on offshore structures. It
is centerloaded to be resonant at approximately 500 KHz for operation between l90 and 415 KHz
and at approximately 900 KHz for operation between 415 and 625 KHz. Tuning below the reso-
nant frequency is accomplished with the antenna coupler. There are two versions of this antenna;
one designed to be mounted on land, the other on drilling platforms or ships. Neither antenna
requires guying. A capacitive hat at the top of the 34-foot Mast Antenna consists of six 8-foot
radials. These can be shortened if necessary for clearance on drilling platforms. The counter-
poise system used for land installations consists of sixteen 60-foot radials made of #10 copper
wire with 6-foot ground rods at each end and one in the center. The offshore version of the Mast
Antenna uses the platform structure and the water for the ground system.
The range with the Mast Antenna and this transmitter depends on ground condition, frequency,
the ADF, and atmospheric noise which in turn depends on location and time. Range for most
locations in the United States with one of the lower priced ADF's is from 50 to 70 miles for fre-
quencies above 250 KHz except over low conductivity ground. SAC does not recommend this
the ADF, and atmospheric noise which in turn depends on location and time. Range for most
locations in the United States with one of the lower priced ADF's is from 50 to 70 miles for fre-
quencies above 250 KHz except over low conductivity ground. SAC does not recommend this