Model HC-114

photo Gates HC-114 In this new 250,000 watt high frequency broadcast transmitter, complete tuning to any one of twenty channels or, with optional synthesizer, to any frequency between 3.95 Mc. and 26.5 Mc. can be made in 20 seconds or less from either a local control or a remote console located up to two miles from the transmitter. The automatic tuning feature eliminates most of the down time for frequency change which can now be performed in the same amount of time normally used for station breaks. This time saving provides as much as one hour per day of additional on air programming for short wave broadcasters. The result is much more efficient operation due to maximum utilization of frequency and program schedule.

DESIGN: Originally developed for Voice of America long range high frequency broadcast service, the Model HC-114 transmitter delivers 250,000 watts of R.F. carrier power at any frequency between 3.95 and 26.5 mc. Plate modulated, the transmitter is capable of 100% amplitude modulation on a continuous basis.

Transistor circuitry, rapid 20 second automatic tuning, vapor phase cooling, and trapeziodal modulation are combined with all of the most advanced state-of-the-art techniques in this outstanding new product.

FEATURES: High efficiency, high reliability and low maintainability have been achieved in the powerful HC-114 high frequency transmitter.

In addition to unique operating and design features, other advantages include:
  1. Use of a 12 phase power supply that requires no filter reactor and increases low frequency audio response.
  2. A newly designed variable inductor with no sliding contacts.
  3. An optional 2 mile remote control system with facilities for returning frequency and modulation information to the control site.
  4. Supply of a portable test console, as a standard item, which can be moved to any point within the equipment and is capable of essentially complete operational controls for simplified servicing and adjustment of the transmitter.
  5. A gang balanced four section harmonic filter with total rejection of harmonics in excess of 80 db.

CONSTRUCTION: The HC-114 transmitter consists of the following major functional sections: The radio frequency source and amplifier chain, the audio modulator, the power supplies, control circuitry including the operating console, and the heat exchanger and cooling systems. The heat exchanger may be placed on the roof of the building and the local control console may be located up to 150 feet away from the transmitter room. Maximum area required is less than 1000 sq. ft.

R.F. CIRCUITS: The radio frequency channel begins with two solid state crystal oscillators, each with 10 selectable crystals, which drive three multipliers to generate the output frequency between 3.95 mc. and 26.5 mc.

This frequency is amplified by an 8122 buffer stage to provide radio frequency drive to the 4CX15,000 intermediate power amplifier. There is provision for two synthesizer inputs in the exciter.

The final radio frequency power amplifier consists of two 4CV100,000C vapor phase cooled tetrodes in a grounded grid input circuit and a unique push-pull output tank circuit. Tetrode vacuum tubes are used throughout to reduce the number of stages of amplification and to ease the neutralization requirements.

Tuning is accomplished by automatic bandswitching in low level broadband stages and prepositioning and closed-loop servo tuning for the intermediate power amplifier and power amplifier stages. A digital to analog converter is used to provide information for automatic inductor and capacitor tuning.

Harmonic suppression is accomplished by a five-section tunable low pass output filter positioned by programmed instruction from digital frequency selection. Spurious signal radiation does not exceed - 80 db. There are no sliding or rolling contacts in use while the power is on.

AUDIO MODULATOR: A +10 dbm. level broadcast quality signal is fed into a triode voltage amplifier which drives an 8122 Class A push-pull driver RC-coupled to the grids of the Class ABl 4CV100,000C modulator stage. The output network transfers the audio power to the R.F. amplifier and also supplies modulation to the IPA driver stage.

Several valuable features provide linearity of opertion, high efficiency, circuit simplicity, and economics in initial costs. These features include voltage and current feedback, extremely low unbalanced direct current in the modulator output transformer, no taps or extra windings on the output transformer, and lower losses in A.C. return paths. Ample reserve power capacity to 294,000 watts under trapeziodal wave modulation will aid in cooler operation and greater reliability.

POWER SUPPLIES: All power supplies are 100% solid state. Designed with a generous reserve capacity to meet trapeziodal modulation requirements the power supply provides greater protection from power line and load transients. The high voltage supply consists of two 7.5 KV. supplies in series rated at 38 amps in a 12-phase system. Oil cooled semiconductor rectifiers are used throughout. This design provides smaller components, less costly maintenance, and easier installation.

Power supplies for the modulator and R.F. amplifiers are designed to be installed within a wire-screened enclosure approximately 16 feet wide by 25 feet long and no more than 12 feet high. This arrangement allows complete accessibility to all components with a lift truck. Main line breakers are mounted in a separate vault and are capable of interrupting 150 Mva. Extensive use is made of interlocking protective circuitry to achieve a high degree of safety for personnel and equipment.

CONTROL CIRCUITRY: Automatic control circuitry is mounted in a relay rack with the exciter units. The main programmer and logic controls are simple and direct. Basically, the digital to analog converter develops commands to tune the complete R.F. chain of the transmitter. All servo amplifiers are solid state and are directly interchangeable. Manual override is provided so that in event of servo failure the transmitter can be tuned manually.

As standard equipment, a control console with full operation capability is supplied with the transmitter for use up to 150 feet from the transmitter room and aids materially in operating ease and quick servicing.

The portable test station which controls the transmitter operation can be plugged in during the maintenance period. All major meter values are monitored and operating adjustments and test at any point within the transmitter room can be made. The value of this aid will be appreciated by station engineers.

Protective circuitry is completely integrated with the automatic control system and manual override on all servos gives 100 percent back-up. In addition, a turns counter driven by the control gearing will provide records of settings for all frequencies.

COOLING SYSTEM: Ambient air is used for forced air cooling throughout the equipment, with the exception of the final R.F. tank inductor and the vapor-phase 4CV100,000C tubes used in the R.F. final amplifier and modulator stage.

All incoming air is filtered. The main heat exchanger system for the vapor phase tubes is an air-cooled condenser which can mount outdoors on the roof of the transmitter building.

Power Output 250,000 Watts
Frequency Range 3.95 Mc. - 26.50 Mc
Frequency Stability ±5 ppm
Tuning Time 20 sec. max.
Carrier Shift 5% max.
Output Impedance 300 ohm balanced
VSWR 1.5 to 1.0
Modulation Capability 100% trapezoidal
Modulation Duty Factor Continuous
Audio Input Level +10 dbm
Audio Input Impedance 600/150 ohms
Audio Response 50-10,000 cps., ±2 db
Audio Distortion 5% maximum
Noise Level -50 db. unweighted
Harmonic & Spurious Radiation -80 db. or better
Power Input Voltage 4160 V ±3%, 3 phase, 3 wire, 50 or 60 cycles as ordered
Power Factor .94
Power Consumption 0% modulation 400 KW. approx.
30% modulation 500 KW. approx.
100% modulation 590 KW. approx.
Over-All Efficiency Approximately 55% at 100% modulation
Altitude Sea level to 6,000 feet.
Temperature 0°C to +50°C
Humidity 0-95% max
Packed Weight 52,000 lbs.
Cubage 2899
Size Power amplifier 20' L. x 8' H. x 7' D.
Modulator 6' L. x 7' H. x 6' D.
Power Supply 16' L. x 25' W. x 12' H.
Size of Largest Unit 20' L. x 8' H. x 7' D.
Cooling Vapor phase cooling for power amplifier and modulator. Closed circuit water for PA inductor. Other units forced air cooled
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
2 4CV100,000C 2 4CV100,000C
1 4CX15,000A 2 8122
2 8122 2 6CG7
1 8072 - -
5 8203 - -


ITU Country
ITU Country