SW-50 A, 50,000 Watt Short Wave Broadcast Transmitter

photo Harris SW-50 A * High level PuIse Duration Modulation

* Exceeds 57% overall efficiency

* 10-Channel pre-set tuning, crystals included

* Low power consumption

* Only five tubes for 50 kW

* Vapor phase cooling

* Designed for trapezoidal programming

* Minimum floor space

* Full front and rear accesssibility

Harris' SW-50 A is a high-level, plate modulated short wave broadcast transmitter, featuring automatic 10-channel pre-set tuning. Utilizing the exclusive Pulse Duration Modulator, the SW-50 A provides higher efficiency, lower operating costs and overall performance superior to that of any other short wave transmitter in the 50 kilowatt power range. The transmitter is capable of operating at any frequency between 3.2 and 22 MHz.

HIGH EFFICIENCY......EXCEEDS 57%. The Pulse Duration Modulator employed in the SW-50 A is almost 90% efficient (instead of the usual 50% to 60%), enabling the transmitter to achieve an unusually high overall efficiency of greater than 57%. This means about one third less power consumption than that of other high level plate modulated 50 kW transmitters.

10-CHANNEL PRE-SET TUNING. Few controls and ample metering make the SW-50 A the easiest tuning high power transmitter available. The servo system will automatically tune to any of ten pre-set channels in about 20 seconds. Auxiliary switching is possible for each channel for antenna switching, synthesizer programming, etc. Up to ten different frequencies from 3.2 to 22 MHz can be remembered, which allows pushbutton re-tuning to any pre-set frequency.

FIVE TUBE DESIGN. The entire transmitter employs just five tubes, with modern ceramic 4CV50,000E tetrode power tubes operating below manufacturer's dissipation ratings. All power supplies utilize long-life solid-state silicon rectifiers. Highest quality components, conservatively rated, are used throughout the SW-50 A to assure a maximum degree of reliability. An integral hoist has been provided for ease of tube handling.

HIGH AVERAGE MODULATION CAPABILITY. The transmitter is capable of sustained high average modulation such as that experienced with trapezoidal audio processing-which means greater loudness at the receiver without increased transmitter carrier power. This is a feature of the high efficiency, DC coupled PDM modulator that avoids the use of large, inefficient transformers in the modulation process. Another feature of this high efficiency series type modulator is convenient front panel carrier power adjustment over a wide range.

VAPOR PHASE COOLING. The SW-50 A employs the vapor cooling technique. This highly efficient method of heat transfer results in constant anode temperatures and extended tube life. This system allows a much smaller and more efficient heat exchanger than older water cooling systems.

MINIMUM FLOOR SPACE. Due to the elimination of large iron core components such as the modulation transformer and modulation reactor, the SW-50 A requires only 7 square meters (76 square feet) of floor space. Advanced cabinet design provides easy accessibility to all components.

RF SECTION. The RF chain is conventional using a transistorized oscillator and RF amplifier, and a 4CX1500A tetrode tube amplifier to drive a single 4CV50,000E tetrode Class C power output stage.

An automatic drive control maintains the PA screen current at a pre-set value, eliminating the usual problem of over-dissipating the screen of a tetrode during tune-up.

THE MODULATION SYSTEM. Harris' Pulse Duration Modulator is characterized by low plate dissipation and low peak tube currents; peak cathode currents are about one-half that of other 50 kW transmitters. Average plate dissipation runs substantially below rated levels, and all peak voltages are maintained well below component ratings.

Wide frequency response is possible as large reactive components are not used in the modulation system. Control of the transmitter power output over a wide range is accomplished in a low-level stage of the modulator by means of a convenient front panel vernier control. No adjustment is necessary in any high power RF circuit.

PROTECTIVE CIRCUITS. All major components of the SW-50 A are protected by circuit breakers. Tubes and transistors are guarded by overload relays or current-limiting devices.

A quick-acting circuit protects against damage by high voltage arcs by limiting the energy in such arcs to less than 10 watt seconds. Protection against voltage standing wave ratios of greater than 2.0 to 1.0 is provided. Both forward and reflected power are metered at the front panel.

In case of momentary RF overloads the SW-50 A will recycle three times automatically. Should a third overload occur within a thirty second period, the transmitter will remain off until manually reset. However, if the time between overloads is greater than thirty seconds, continuous recycling will occur.

The SW-50 A employs a unique method of transmitter protection. The modulator tube may be turned off in a low level state in about five microseconds. This removes the HV from the PA tube, thus eliminating most faults which normally occur. The HV supply (diodes and transformer) is capable of withstanding repeated short circuits without harming the unit.

An automatic gain control monitors the PA screen current. The PA may be operated with no HV but with screen voltage and under any condition of tuning with no damage being done to the PA tube.

Additional protection is provided by the HV circuit breaker. Tubes and transistors are also protected by current limiting impedances.

THE SERVO SYSTEM. The all solid-state servo system will automatically tune any of 10 pre-set channels in about 20 seconds. Each channel is "remembered" on one plug in card. Auxiliary switching also is provided on each pre-set channel card for antenna switching, programming, etc. The fast tuning time is made possible because the HV supply is not disabled during the tune cycle; the RF drive is turned off in a low level solid-state stage, and all tuning is done in parallel. When the tuning has been accomplished, the modulator is turned back on silently and smoothly.

TRANSMITTER LAYOUT. The standard SW-50 A consists of two cabinets, a remote heat exchanger and an external high voltage power transformer and voltage regulator. Front doors and meter panel are magnetically latched.

Power Output 50,000 watts nominal unmodulated
RF Frequency Range 3.2 to 22.0 MHz
Method of Tuning Manual, or selection of 10 pre-set channels
RF Output Impedance 300 ohms balanced, 2.0 to 1 maximum VSWR
RF Frequency Stability ±1 x 10-6 (±22 Hz at 22 MHz)
Spurious and Harmonic Emission Less than 50 mW
Carrier Shift Less than 2% at 95% modulation at 1000 Hz
Audio Frequency Response ±1.5 dB from 50 to 10,000 Hz referenced to 1,000 Hz at 95% modulation
Audio Frequency Distortion Less than 3% from 50 to 10,000 Hz at 95% modulation
Noise 55 dB below 1,000 Hz, 100% modulated level
Audio Input Level 0 dBm ±2 dB for 100% modulation
Audio Input Impedance 600/150 ohms, balanced or unbalanced
Modulation Level 100% sinusoidal, 60 minutes, 500-5000 Hz
Trapezoidal Modulation Less than 5% tilt or overshoot, 100 Hz to 2000 Hz measured using 12 dB clipped sine wave
Power Input Any specified voltage 380V to 480V, 3 phase, 50 or 60 Hz. Phase unbalance 5%, Regulation 5%
Power Consumption No Modulation: 89 kW
30% Modulation: 92 kW
100% Modulation: 130 kW
Power Factor Greater than 95%
Voltage Regulator Electronic voltage regulator for all power supplies other than high voltage
Overall Efficiency 57% or greater @ average modulation
Temperature Range 0 to +50°C ambient air temperature. Sea level decrease 2°C/1000 ft. altitude (38°C @ 6000 ft.)
Humidity 95% relative humidity, maximum
Storage Temperature -35°C to +60°C
Altitude Up to 1829 meters (6000 feet) above sea level
Cabinet Data The two main cabinets measure 366 cm (12 feet) wide, 137 cm (4.5 feet) deep, and 304 cm (10 feet) high
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
1 4CV50,000E 1 4CV50,000E
1 4CX1500A 1 4CX1500A

1 F-1099


ITU Country
ITU Country