• 521 Rotatable Log-Periodic Antenna


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    • Abstract: 521 Rotatable Log-Periodic AntennaAchieve greater bandwidth and compact, easily erected antenna that has been ❯ Hydraulic and control units atperformance with a compact structure. providing highly reliable service since it was

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521 Rotatable Log-Periodic Antenna
Achieve greater bandwidth and compact, easily erected antenna that has been ❯ Hydraulic and control units at
performance with a compact structure. providing highly reliable service since it was
ground level
A rotatable HF log-periodic antenna serves as introduced in 1973.
a general-purpose solution. In this role, it must Transmit and receive versions of the 521 are ❯ All necessary erection
come as close as possible to the performance available covering the 4 to 30 MHz bandwidth. A equipment included
specifications of fixed directional antennas high-power version of the antenna covering 5.95
in terms of gain, bandwidth, power-handing to 26.1 MHz is also available for use at shortwave ❯ Most assembly performed at
capability, front-to-back ratio, and reliability. All of broadcasting stations. ground level
these performance requirements conflict directly
with the economic and physical requirements K E Y F E AT U R E S ❯ All-aluminum construction
regarding reliability, erectability, size, and ❯ Medium- and long-range coverage ❯ Special rotator assembly used by
cost. For example, the desire to serve lower heavy-duty industrial cranes
frequencies reflects itself directly in a much larger ❯ 70° Cardioid beamwidth
radiating structure. In general, structural loads are ❯ Compact, rugged and easy to erect
proportional to the square of the largest linear
❯ Fully adjustable azimuthal direction
via rotator ❯ Eliminates the need for multiple
dimension of the radiating structure. Thus, a
antennas
lower cut-off frequency puts expensive demands ❯ Fully efficient: 2.0:1 VSWR
on the size, cost, and erectability of the antenna. ❯ High-environment version available
TCI’s unique design techniques have achieved ❯ Wide bandwidth: 4–30 MHz for
a new standard in terms of bandwidth, gain, transmit, full 2–3 MHz for receive only
VSWR, and front-to-back ratio for a given-
size structure. The result is the Model 521—a
521 System Details
Radiating Assembly Azimuth and Elevation Patterns – gain in dBi
The 521’s radiating assembly is a wire-strung,
transposed dipole, log-periodic antenna. The
elements are compound (i.e., made up of
more than one wire) and, thus, have a low Q.
Typical azimuth pattern in the plane of the first beam from the ground.
This results in an improved VSWR, gain, and
front-to-back ratio for a given amount of wire
disposed within the envelope of the radiating
structure. The antenna uses highly corrosion-
resistant materials. Radiator wires are made from
Alumoweld, including the support catenary, which
is segmented by high-strength, glazed alumina
ceramic insulators, and is employed as part of the
radiating structure. Thus, all structural members
are involved to the maximum extent possible in
improving and optimizing the antenna’s radiation
performance. The masts and booms are made
from 6061-T6 aluminum alloy. The support
booms are aluminum tower sections, which
minimize the wind drag of the structure. The
radiating structure, balun, and rotating joint weigh
a maximum of 3000 pounds (1360 kg, 110 mph).
Rotating Joint and
Balun Assembly
The balun assembly is one of the standard
antenna drive units manufactured for many years
by TCI. A coaxial rotating joint is also employed.
It has proven to be especially long-lasting and
trouble-free.
The TCI Model 521—a compact, easily erected
antenna that has been providing highly reliable
Rotating System service since it was introduced in 1973.
The antenna rotation system is highly reliable subject to great loads in heavy-duty construction
and easy to maintain. The rotators are hydraulic work in a wide range of environments.
motors of the type used in construction cranes The vast commercial experience with this
and marine winches. The hydraulic power pack hydraulic and bearing assembly ensures the
and control unit are near ground level, making it mechanical integrity of the system. At TCI, this
easy to perform maintenance. proven technology has been applied to the 521
The usual rotating assembly, consisting of an antenna, and replaces the more traditional and
electric motor, clutch, gear train assembly, and unreliable clutch and gear system. In addition,
special bearings, has been a continual source since a hydraulic system is essentially constant
of unreliability and difficulty. The 521 employs a torque, it provides smooth starting and braking
very conservative, exhaustively proven hydraulic action and avoids the very high inertial loads
bearing and rotating system. This system has been associated with a conventional clutch-and-
employed for many years on industrial cranes gear system.
System Details 521
Figure 1: Completed assembly – rotatable position Figure 3: Rotatable curtain shown in erection
position
Erection and
Configuration
The 521 employs an erection procedure with two
very important safety and performance advantages:
❯ A 40-foot (12.1-meter) erection tower that is
in continuous contact with the main antenna
support tower during erection and lowering.
The loads in the erecting cables are a small
Figure 2: 90-foot tower shown in erection position fraction of those in older designs.
❯ The antenna and tower are completely erected
and permanently guyed before it is necessary
to climb the tower to complete the final
connections.
Figures 1 through 3 illustrate the antenna
configuration and erection. General configuration
is shown in Figure 1. Figure 2 illustrates the first
step in antenna erection. The antenna support
tower is erected on the ground. The radiating
curtain assembly is assembled and attached
to the support tower on the ground. The 40-
foot tower is erected. Side guys are installed to
stabilize the support tower during lifting. A double
pulley arrangement is used between the 40-foot
erection tower and the main support structure.
The maximum tension in the erection lines during
the process of raising the support tower and
High-Frequency Rotatable LPAs are during erection or operation. Improper the possibility of fasteners loosening,
complicated electro-mechanical devices. power voltage can cause failure of the components fatiguing, or material failing
radiating structures is 3000 pounds (1360 kg).
They are subject to failure in adverse controls or components of the antenna. is high. Proper maintenance is required The antenna kit includes a manually operated
environments and require considerable Periodic maintenance and an adequate for antenna safety. Fixed antennas such winch for raising and lowering the antenna.
maintenance. Before purchase, the supply of spare parts are required. as the TCI 540 Omni-Gain antenna
following facts should be considered: are a much better choice in such
❯ Rotatable antennas of this size are environments for a trouble-free operation.
❯ During installation of the antenna, designed for normal weather conditions If a rotatable antenna is installed in a
instructions in the installation drawings where storms may occasionally occur. hostile environment, frequent periodic
and manuals must be followed exactly. If the antenna is subjected to hostile maintenance is required to repair
Improper installation of concrete or environments, such as constant high minor problems before they can cause
rigging of the antenna can result in failure buffeting winds or corrosive elements, catastrophic failures.
521 Summary Specifications
An SPX Company
Model 521 T C I I N T E R N AT I O N A L , I N C .
3541 Gateway Blvd.
Specifications Fremont, CA 94538-6585 USA
TEL: 1-510-687-6100
Polarization Horizontal USA: 1-800-824-8074
Gain of Principal Lobe 12 dB nominal 4–30 MHz FAX: 1-510-687-6101
8 dB at 4 MHz www.tcibr.com
Front-to-Back Ratio 13 dB minimum
4.6 to 30 MHz
Azimuth Beamwidth 70° nominal
Side Lobe Level –13 dB maximum
Input Impedance 50 ohms nominal
VSWR 2.0:1 maximum
Speed of Rotation 0.4–1 RPM (0.5 RPM for 521-4-100)
Rotation Positions 12
Designed in accordance with EIA Specification RS-222C
Environmental Performance
to withstand force of 177 km/h (110 mi/h) wind, no ice
(see note on page 3)
or 145 km/h (90 mi/h) wind, 0.6 cm (1/4”) radial ice
225 km/h (140 mi/h wind, no ice), 145 km/h (90 mi/h) wind,
Optional
0.6 cm (1/4”) radial ice
Rotating Assembly Hydraulic
521-1-N: 5300 lbs. (2404 kg)
Weight
521-4-100: 12,300 lbs. (5579 kg)
521-1-N: 216 cu. ft. (6.1 cu. m)
Volume
521-4-100: 583 cu. ft. (16.5 cu. m)
❯ Size
Height Length* Boom Length Guy Radius*
Model Number Frequency (MHz)
ft. m ft. m ft. m ft. m
521-1-N 4–30 109 33.2 102 31.1 110 33.5 80 24.4
521-4-100 5.95–26.1 109 33.2 102 31.1 110 33.5 80 24.4
* Measured from extreme guy points
❯ Power and Impedance Data
Model Number Impedance Power Connector
521-1-06 50 ohms Receive up to 1kW PEP Type N Female
521-1-03 50 ohms 10 kW Avg/50 kW PEP 1-5/8” EIA Female
521-4-100 300 ohms 150 kW Avg/400 kW PEP Balanced
* Additional 160 feet required to lower antenna.
Company proprietary
Data and specifications subject to change without notification
Not for distribution without prior permission from TCI.
521-11-05-12
©2004-2012 TCI—All Rights Reserved


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