CONTINENTAL ELECTRONICS 418 E

GENERAL DESCRIPTION

418 E 100 kW Shortwave Transmitter
photo Continental Electronics 418 E

1 INTRODUCTION

The Continental Electronics Type 418 E 100 Kilowatt Shortwave Broadcast Transmitter has been designed to provide high quality performance and optimum efficiency in the shortwave frequency bands designated by the International Telecommunication Union.

1.1 DESIGN FEATURES

Continental Electronics' vast knowledge and background in the design, development, manufacture, installation, and operation of high-power and super-power transmitters have been fully utilized in the design of our Type 418 E Transmitter.

Only long-term reliable components and electron tubes are utilized. The application of simple field-proven circuitry has resulted in a modern shortwave broadcast transmitter which is capable of providing excellent overall efficiency.

Salient features of the Type 418 E Transmitter are:

Fast frequency change is provided with selection of up to 10 pre-selected frequencies. Tuning to a new frequency is extremely easy because only five controls are used. After tuning is accomplished and one of 10 frequencies is preset, returning to that frequency is accomplished by activating one button on the front control panel.
A broadband solid state RF amplifier is used to drive the IPA amplifier.
Water cooling of the final amplifier tube is highly efficient and provides stable cooling ensuring longer tube life.
Maximum reliability due to minimum number of high gain amplifier stages; final power amplifier (4CV100,000C tube) is being operated at less than 25 percent of its rated plate dissipation.
Highly efficient solid state modulator which provides superior audio performance.
Controlled Carrier Modulation (CCM) available, at operator selection with up to carrier level reduction of up to 6 dB during program pauses.
Built-in Single Sideband capability using phase amplitude system for a PEP program output power of up to 300 kW. (OPTIONAL)
The power supplies all use highly reliable and efficient semiconductor devices as rectifiers.
Individual instrumentation for all important electron tube functions, rectifier output voltages, primary power voltage and elapsed operation time.
Comprehensive supervisory control and equipment protection system with illuminated pushbutton status signals for all important operating and fault conditions.
Automatic personnel protective system interrupts, then grounds all dangerous voltage when an access door is opened in accordance with IEC 215 specification.
Continuous full power operation with specified performance over wide range of environmental conditions.
Compact cabinet design requires a minimum of floor space. Full width doors permit easy maintenance access. Cooling and high voltage equipment occupies a small area near the transmitter cabinets.

2 RF CIRCUITRY

2.1 RF GENERATOR

The radio frequency generator (synthesizer) is located in the control cabinet.

2.2 FIRST RF AMPLIFTER STAGE

The solid state RF amplifier consists of a single ended transistor stage driving two other push-pull transistor stages for a gain of 35 dB. All three stages are broadband and no tuning is needed from 3.2 MHz to 22.0 MHz. The input stage is a 2N3866 transistor transformer coupled to two (2) MRF433 transistors. The 16 volts DC for these two stages is obtained from the series path regulator made up of a 2N3054 transistor. The MRF433 stage is also transformer coupled to the output stage consisting of two PT9780 transistors that operate with 28 volts DC on the collectors. The output of the PT9780 is transformer coupled to the input of the IPA amplifier. The 2N3866 stage is operated in Class A and the other two stages are operated quasi Class B.

2.3 RF DRIVER AMPLIFIER (IPA)

The Eimac Type 4CX3000A tetrode tube is utilized in this stage. The tube is a forced air-cooled ceramic and metal electron tube which is used in a grounded grid circuit. This configuration provides a broadband load for the solid-state amplifier and requires no neutralization.

The plate tuning circuit is a conventional parallel tank which is capacitively coupled to the final RF power amplifier.

The tuning components are geared together and driven by a single motor which permits continuous tuning of the intermediate power amplifier from the front panel control.

The power output capability of the RF driver stage is approximately 3 kilowatts, which is more than adequate to drive the final RF modulated amplifier.

2.4 RF FINAL POWER AMPLIFIER

An Eimac Type 4CV100,000C tetrode tube is utilized in the RF final power amplifier. This tube is a water cooled ceramic and metal electron tube. The tube is employed in a conventional grounded cathode circuit as a high level plate modulated RF amplifier. The application of the single type (as opposed to multiple tubes) in our uniquely designed circuit, provides the advantages of stability, simplified circuitry, neutralization, tuning over the entire carrier frequency range, and the control of spurious and harmonic emission.

Recent developments in capacitor technology by Continental Electronics allows the screen grid to be by-passed with essentially no reduction in grid/plate isolation. This allows the P/A circuit to be operated as a conventional grounded cathode amplifier with all its attendant circuit simplicities while maintaining unconditionally stable operation.

The DC plate blocking capacitor uses a special dielectric material. This capacitor is used in the shunt fed plate circuit. This special design was created by Continental Electronics because of its experience with vacuum blocking capacitors where large RF currents created heating of the copper plate inside the capacitor causing emission problems and creation of potential destructive arcing when a DC voltage exists across the capacitor.

The plate of the 4CV100,000C tube is tuned with a high "Q" parallel resonance circuit which uses a motor-driven variable vacuum capacitor and band switched inductor. The eleven inductor bands can be selected from the front panel with total band change time of less than 1 minute. Neutralization is accomplished with capacitance coupling between the plate and the cold end of the intermediate power amplifier tank using the familiar bridge neutralizing technique.

The power amplifier tank circuit is a Pi-L section. Tuning of the final stage is accomplished with motor driven vacuum variable capacitors controlled from the front panel. The tank inductor provides 11 bands between 3.2 and 22 MHz. The pi-loading capacitor and L-network components are ganged together for loading. The arrangement of output circuitry provides flexible operation and very good harmonic attenuation.

3 MODULATOR

The Type 418 E Transmitter is equipped with a solid state modulator. The absence of vacuum tubes provides enhanced overall efficiency and exceptional audio performance. The modular configuration of the system permits redundancy and gradual lowering of the transmitter output power level in the event of a switching module failure. Loss of one switching module results in only a two percent reduction in transmitter output power. Normal transmitter operation continues uninterrupted, thereby improving transmitter reliability. Maintenance is simplified by LED module fault indicators that identify a defective module, permitting repair or replacement during normal maintenance periods. An overall modulator efficiency of greater than 95% is assured through the use of conservatively rated, state of the art semiconductors (insulated gate bipolar transistors).

The rapid switching capability of the modulator provides overload protection for the RF power amplifier tube and associated power amplifier components without the use of a crowbar circuit. The nature of the switching circuits offers superior protection without the heavy overload currents encountered with crowbar circuits.

A further attribute of the solid state modulator is its audio performance. In the audio bandwidth of 50 to 7500 Hz, modulator distortion is less than 1%. Squarewave performance of less than 5% tilt or overshoot assures an accurate reproduction of complex audio processing. Signal to noise ratio of the modulator is better than -60 dB.

The modulator is capable of supplying PA anode voltage at any level required to operate the transmitter up to a power output level of 100 kilowatts. The power output level of the modulator is controlled by "Raise" and "Lower" switches that adjust the level in 0.1 dB steps. The power output level is adjustable from the transmitter control panel or from a remote location. Additionally, full power operation or any predetermined value of reduced power is selected with "High Power" and "Low Power" switches.

A standard feature of the transmitter is controlled carrier modulation (CCM) operation. CCM is selectable from a panel-mounted switch on the transmitter control panel. Switching between normal and CCM modes is accomplished without interruption of transmitter operation.

Another standard feature is single sideband modulation (SSB) using the phase/amplitude method. This method provides the high efficiency of class C operation, together with high signal quality. When compared to a transmitter using the push-pull class B plate modulator, the solid state modulator replaces the following items:

High voltage plate supply for the modulator and RF power amplifier.
Push-pull modulator amplifier with its two high power tubes and driver circuits.
Modulation transformer and modulation reactor.
High voltage filter capacitor bank.

The modulator consists of 48 series connected power supplies which can be individually switched on or off to provide the DC voltage output necessary for the carrier level or any desired depth of modulation up to 100%. An audio filter follows the switching modulator to remove the switching signals and allow the DC and audio signals to pass to the RF amplifier.

3.1 700 VOLT SWITCH MODULE

The 3 phase input power is isolated by the power transformer, and fused to protect the power module. AC to DC rectification is provided by 3, full wave diode modules. DC energy storage is provided by computer grade electrolytic capacitors. The fault protection transistor is normally in a conducting mode. Local control circuitry monitors the performance of the switching transistors. If the switching transistor is found to be non functional the fault protection transistor will be commanded open. The switching transistor follows the commands from the modulator controller for either zero or 700V output. The clamp diode allows the load current to pass when the switching transistor is off.

3.2 MODULATOR ASSEMBLY

3 phase primary power is supplied to the two transformer primaries. Resistive step starting is used to reduce the capacitor charge current surge. The 48 switch modules are series connected, and powered from the multiple isolated secondaries. Series inductors interconnect the switch modules to limit short circuit currents. The output is connected to a low pass filter to remove the switching carrier which is already 30 dB down. The modulator return current is monitored to protect the modulator, and the load, from short circuit currents. Reaction time to load faults is less than 5 microseconds.

4 INSTRUMENTATION

The Type 418 E Transmitter is fully instrumented and all important operating parameters are displayed on large scale, easy-to-read, meters which are mounted on the front panel of the transmitter. The meters are grouped in a functional and logical manner. There are 12 meters located on the transmitter.

4.1 CONTROL SYSTEM

The operation of the Type 418 E Transmitter is simplified through the use of push-button control switches which have built-in illuminated function designated labels that change color to indicated the status.

The overall control circuitry is a series-parallel ladder network to provide for a comprehensive protective system.

The preset tuning system for the Type 418 E Transmitter utilizes DC motors which are controlled by solid state DC power amplifiers. The tuning system is actuated by a push-button switch on the transmitter control panel which selects the desired preset tuning position for each driven component. Multi-turn digital readout potentiometers are provided on the control panel for initial positioning and manual tuning.

4.2 PERSONNEL PROTECTIVE SYSTEM

The personnel protective system incorporated in the Type 418 E Transmitter is designed for maximum safety. It was designed for compliance with IEC-215.

The opening of any door will automatically remove all dangerous voltages within the exposed area, then ground the associated conductors and high voltage capacitors. Shorting sticks with a grounding hook are permanenfly located in the power vault and modulator. The operator can use these to place on high voltage conductors as a double safety precaution prior to working in the cubicle.

5 MECHANICAL DESCRIPTION

5.1 COOLING

The radio frequency final power amplifier Type 4CV100,100C tube uses a water cooling system.

The only cooling system component external to the transmitter cabinets is the water-to-air heat exchanger assembly. This may be mounted inside the building or on the roof up to a distance of 10 meters and connected to the 418 E with the standard set of installation materials supplied with the transmitter. The total heat dissipated by the condenser is 45 kilowatts with the transmitter sinewave modulated 95 percent.

5.2 FORCED AIR-COOLING

The forced air-cooling system inside the transmitter cabinets is exhausted from the top of the cabinets. The heat discharged by the air system and radiated by the transmitter cabinets is under 5 kilowatts with the transmitter sinewave modulated 95 percent.

Heat radiated from the power equipment in the high voltage room is 3 kilowatts, or when the transmitter is being sinewave modulated at 95 percent.

A centrifugal blower in the radio frequency power amplifier cabinet supplies forced cooling air for the Type 4CX3000A electron tube and other components employed in the radio and audio frequency stages of the transmitter.

The air intake is located at the bottom back door of the power amplifier cabinet and the discharge is through grilles at the top of the cabinets. The top vents of the transmitter cabinets can be common ducted to atmosphere. Continental Electronics engineering services are available to assist the customer in the overall plant design.

The switched supplies of the modulator are arranged in three stacks or towers in a manner which allows cooling air to be forced up the center of the towers.

5.3 ACOUSTIC NOISE LEVEL

The cooling system is silent with the exception of the external heat exchanger fan which is a large air volume low velocity type with low noise level. The acoustic noise level from the forced air blower in the transmitter cabinet is also extremely low.

5.4 CABINET DESIGN

Cabinets utilize heavy gauge steel construction, chemically treated with appropriate rust inhibitives. Each cabinet is of the modular free standing type, which may be installed in line for a composite assembly. The design has a logical division of circuitry and mechanical components.

Aluminum shielding inside cabinets, in all areas of critical radio frequency circuitry, assures minimum interaction and prevents stray radiation.

5.5 EQUIPMENT IDENTIFICATION

Equipment identification is cross-referenced to Continental Electronics unit numbering system and is related to the electrical and mechanical parts lists with the transmitter.

The circuit reference for each component is stamped on the chassis adjacent to the component and the component description and rating is identifiable from the associated parts lists. All controls and metering functions are designated with appropriate titles on the front panel of the transmitter.

5.6 FINISH

All metal parts are suitably plated or treated with corrosion or rust inhibitives. The final finish is extremely durable and scuff resistant. Ornamental trim is applied to certain areas of the front panel to enhance appearance and present a modernistic design.

6 ENVIRONMENT CONDITIONS

The Type 418 E Transmitter will perform as specified when subjected to the following environmental conditions in any normal combination.

6.1 ALTITUDE

Up to a maximum of 6000 feet above mean sea level.

6.2 TEMPERATURE

Any ambient temperature within the range +5 to 40 degrees C.
(33.8 to 104.0 degrees F). (Higher temperatures on special order.)

6.3 HUMIDITY

Relative humidity up to 95 percent.

6.4 DUST

The cabinets and doors are well sealed against the admittance of dust particles. The forced air electron tube cooling system has adequate air intake filters. As dust filters for the steam condenser air intake system are not supplied as part of the equipment, such filters should be selected to be compatible with the site environmental conditions.

7 INSTALLATION

Installation requirements permit easy and fast initial set-up. The four cabinets are usually placed in-line and wiring between cabinets is placed in an internal interconnecting duct. A single floor trench or an overhead wiring duct (not supplied) is required between the transmitter cabinets, modulator and the power vault. The heat exchanger can be wall or ceiling suspended with a single pipe run overhead from the transmitter cabinets. The return water runs through a single pipe.

7.1 POWER SOURCE

The primary power input of 360/480 V, three phase, 50/60 Hz., enters the Type 418 E Transmitter's power distribution cabinet and is distributed via circuit breakers to the main high voltage transformers, steam condenser fan motor and three-phase power which is stepped-down to 230 volts to supply filament transformer, bias and low voltage rectifiers. The 230 volts is further stepped-down to 115 volts for the control circuits.

7.2 MAINTENANCE

All cabinets have single front and double rear doors to permit easy access to all internal circuitry. In the radio frequency stages, where the component layout has to be compact for circuit reasons, easy access is achieved through the use of hinged panels and swing-out compartments. The double rear doors are used to minimize floor space requirements behind the transmitter cabinets.

7.3 INSTRUCTION MANUAL

The instruction manual supplied with the transmitter contains complete operating and maintenance instructions, together with appropriate photographs, line drawings, circuit schematic drawings, and parts list. Two copies are furnished.

Installation instruction with wire running data and typical layout data is supplied separately from the instruction manuals. Continental Electronics will assist the customer with layout problems and provide specific installation instructions, drawings, and materials.

TECHNICAL SPECIFICATIONS
Carrier Output Power	100 kilowatts
Types of Emission	Amplitude Modulation (A3) SSB (A3A) (IF REQUESTED)
Type of Modulation	Solid state step modulator with CCM
Final Power Amplifier	Class "C" operation in both A3 en A3A modes
Frequency Range	3.2 to 22 MHz (2.3 to 16 MHz or 3.95 to 26.1 MHz optional at extra cost)
Output Impedance	75 ohms unbalanced, 300 ohms balanced, (or 50 ohms unbalanced, optional). 2:1 max. VSWR
Modulation Capability	100%, 50 to 5000 Hz sinusoidal
Radio Frequency Harmonic	50 MW (Complies with C.C.I.R. recommendations)
Audio Input Levels for 100% Modulation	+10 dBM, ±dBM at 1000 Hz
Audio Frequency Response	±1 dB from 50 to 5000 HZ
Audio Frequency Distortion	Less than 3% RMS, 50-5000 Hz @ 90% Modulation
Residual Carrier Noise	55 dB (unweighted) below 100% modulation level at 1000 Hz
Carrier Shift	Less than 3% at 100% modulation exclusive of power line variations
Power Consumption	140 kW at carrier 210 kW at 100% modulation
Overall Efficiency (Average)	70 - 72% at carrier and any modulation depth
Primary Power Requirements	360 to 480 volts Three phase 50/60 Hz
Power Factor	Better than 0.95
Specifications may change without notice

TUBE COMPLEMENT
RF stages		AF stages and modulator
Number	Type	Number	Type
1	4CV100,000C
1	4CX3000A

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	BOT	BOTSWANA	CHN	CHINA
	PNG	PAPUA NEW GUINEA	PHL	PHILIPPINES
	TWN	TAIWAN	G	UNITED KINGDOM
	USA	USA	ZMB	ZAMBIA
	ZWE	ZIMBABWE