Continental's 419 F-2, 250 kW Broadcast Transmitter

photo Continental Electronics 419 F-2 Features

* Simplified computer control and operation

* High efficiency pulse-width modulation

* Low loss water cooled output tank inductor

* Efficient multi-phase cooled power amplifier and modulator tubes

* Automatic tuning of 10 preset frequency/antenna combinations

* Dynamic carrier control

* Hardwire remote control capability up to 300 meters

* Conventional AM and SSB capability

General Description

Varian Continental's 419 F-2 is a modern, versatile and high efficiency 250 kW shortwave transmitter designed specifically for international broadcasting service.

Designed for continuous operation, this transmitter can be tuned to any frequency in the international broadcast bands between 3.9 and 22 megahertz in less than one minute. Automatic frequency selection is available or manual tuning for a preset position can be done by a trained operator in five to ten minutes.

The Continental 419 F-2, which is controlled and monitored at a single centralized control panel, is field proven and highly reliable. It is the latest in the 419 series, which have been operating successfully in the field for many years.

The hardwire remote capability can operate at up to a 300 meter distance and can be provided for the following functions:

Remote Commands / Indicators

Indicator reset
High power
Low power
High voltage start
Bias start (standby)
Cooling stop (off)
Channels 1 thru 10

Remote Status Indicators

Overloads (12)
Arc sensors (4)
Reflected power
PA overvoltage
Fault timer
Low water flow
Output prove
Cooling fault summary
Intermittent cooling fault
Interlock fault summary
Intermittent interlock fault

In addition to these remote commands and status indicators, the following indicators are also provided on the control panel:

Commands / Indicators

Tune enable (momentary)
Tune power (on/normal)
Cooling (start)
Filaments (stop/start)
Bias (stop)
Remote control (off/on)
Driver autotune (off/on)

Status Indicators

15 cooling
12 interlock

The three stage RF amplifier consists of a solid state broadband amplifier, a grounded grid 3CW20,000A7 triode and a 4CV250,000C tetrode final power amplifier. The series floating deck pulse-width modulator (PWM) uses a single 4CV250,000C tetrode driven by a solid state MOSFET driver. Excellent noise immunity and HV bridging is achieved by interconnections to the floating deck via fiber optic cables.

Our 250 kW transmitter combines a proven RF amplifier with a highly efficient pulse-width modulator that has been adapted from Continental's 420 B 500 kW shortwave transmitter, also proven to be exceptionally reliable in station operation.

The power amplifier and modulator tube anodes are vapor phase cooled while the RF drive tube anode, PA second modulator grid and filament, modulator driver, broadband amplifier and PA tank capacitor inductors are water cooled. The modulator back swing diode is cooled and protected with insulating fluid and a continuously operating bypass circulation water deionizer is also provided. Forced air is used to cool other components.

Modern switching techniques, which use two proprietary circuits, give the modulator better than 90 percent efficiency with excellent signal fidelity. Overall transmitter efficiency is 66 percent or better depending on operating frequency and ambient conditions.

Simplified Operation

The test of a modern shortwave broadcast transmitter is the ease with which it can perform its mission, regardless of its circuitry and internal components. The 419 F-2 has been designed by Continental Electronics to provide the highest standard of shortwave transmission while maintaining this ease of operation from either a remote or on-site status. The straightforward control system and status indicators virtually eliminate confusion and simplify operation.

The control panel displays the various operating parameters in three separate groups for the drive, modulator and power amplifier for quick and accurate decision making. In addition, all indicators and control operations are arranged on a single control panel.

Efficient, Reliable Circuits

Continental has designed the 419 F-2 to incorporate basic, readily available components so that maintenance is both simple and economical. The entire modulation system is straightforward and easy to operate.

The PA tank coil tuning is accomplished by three sets of shorting plungers driven by three separate control motors. This arrangement provides variation of inductance in one third turn steps. The plungers are coarse tuned with no RF current flowing, after which resonance and proper loading is accomplished by vacuum capacitors, with the power on. The water cooled tank coil and plungers provide an efficient, cool running, trouble free output tuning system.

RF Harmonic Suppression

The PA output is routed to a tuned, automatically preset harmonic filter comprised of variable vacuum capacitors and two spirally wound, water cooled variable inductors. The output of the harmonic filter is connected to a fixed tuned VHF low pass filter to eliminate high order harmonics.

Controlled Carrier Modulation

Continental's 419 F-2 is designed so that a significant savings in power costs can be obtained by using the dynamic feature of controlled carrier modulation. Traditionally, the practice in AM systems has been to provide a fixed carrier level and apply modulation up to 100 percent.

With the Continental system, during periods of low or no modulation, power consumption can be significantly lowered by automatically reducing the carrier level and restoring the carrier level when modulation increases. The controlled carrier level with no modulation can be adjusted for 0 to 6 dB in 1 dB increments.

The controlled carrier modulation feature has the transmitter adjusted for full carrier power output and audio input set at 100 percent modulation with full modulation available. If the audio input level falls, the carrier level will adjust to keep modulation at 100 percent. However, if modulation is totally removed, the carrier level will fall to a pre-selected minimum level. As modulation increases, the carrier level also increases to ensure 100 percent modulation is not exceeded.

Single Sideband Operation

Continental's optional Single Sideband Reduced Carrier (SSBRC) operation is available and accomplished through a refined phase-amplitude modulation technique. The transmitter peak envelope power in this mode is 500 kW and carrier suppression of both -6 and -12 dB is available. This SSBRC circuitry has been developed to provide the signal quality needed for future broadcasting needs in this mode.

High Fidelity

The 419 F-2 is virtually transparent and accepts processed audio without any degradation. Oscilloscope photographs prove our transmitters' extremely high fidelity. The oscilloscope photograph, compares the input audio waveform with the output envelope signal while the transmitter is being modulated 90 percent with a 1 kHz sinewave signal.

Reliable Component

Continental's 419 F-2 incorporates protection features for the prolonged life of the transmitter. High speed sensing can stop the pulse train to the modulator if there is an arc in the PA area or excessive reflected power. A backup to this is an ignition "crowbar" which short circuits the high voltage power supply output within five microseconds after a short circuit is detected in the PA on the high voltage DC bus.

Twelve DC overload detectors also operate the modulator cut-off. They also turn off the high voltage, drive, PA screen and broadband amplifier power supplies. A two stage automatic recycle is available for both modulator cut-off and DC overloads.

The number of faults which will be accepted while operating at high power is preset between zero and nine. When an excess of faults is detected within a certain time period, the transmitter switches to low power. The allowable faults at low power are also set between zero and nine, so if an excess of faults are detected in a specific time period, the transmitter is locked out and the lockout alarm will sound.

Personnel Protection

All doors are electrically interlocked and in addition, a key interlock system requires that all high voltage be turned off and grounded before door keys become available. Interlock ground sticks are provided in all cabinets.


Continental's 419 F-2 transmitter is designed so that the control and low voltage unit has walk-in rear access and the RF circuitry cabinets have both front and rear doors providing complete accessibility for cleaning and maintenance convenience. The modulator unit door may also be opened for servicing.

Several alternative arrangements may be used for locating the power transformers, filament control regulators, modulators and cooling systems for the most convenience and flexibility in working with the customer's facility design.

Carrier Output 250,000 watts, minimum
PEP Output (SSB optional mode) 500,000 watts, minimum
Modulation Pulse-width modulator (PWM)
Emission A3E or A3J (USB)
Frequency Range International broadcast bands, 10 preset channels 3.9 to 22 MHz
Frequency Control Frequency synthesizer
Frequency stability 1x10-8 per day, optional greater stability available on special order
AF Input Impedance 600 Ohms, 30 dB return loss
AF Input Level for 100% Sinewave modulation +10 dBM ±2 dB continuously adjustable, other levels optional
AF Response ±1 dB 50 to 4,500 Hz
±2 dB 4,500 to 6,000 Hz
Referred to 1,000 Hz at any modulation level
AF Distortion Less than 3% THD, 50 to 4,500 Hz at any modulation level up to 100% positive and negative
SSB Option
SSB Carrier Suppression -6 or -12 dB selectable
SSB Unwanted Sideband Suppression -55 dB
SSB Odd Order IM Products -30 dB (two tone test)
Carrier Shift 1.5% or less including power line variations of up to 2%
Modulation Capability 100% positive and negative modulation continuously by program, band limited noise or sinewave modulation 50 to 6,000 Hz at any power level up to 250 kW
Controlled Carrier Modulation 0 to 6 dB carrier reduction in 1 dB increments
Overmodulation Adjustable peak clipping may be set to desired maximum modulation level.
Transmitter will accept input level of 10 dB over 100% without damaging equipment. AF input exceeding 10 dB over 100% modulation level may cause protective overload circuits to operate.
Residual Carrier Noise 55 dB unweighted below 100% modulation at 1,000 Hz measured in a bandwidth of 10 to 15,000 Hz
RF Harmonic and Spurious Output Level Less than 2.5 milliwatts up to a maximum frequency of 900 MHz
Output Impedance 75 Ohm unbalanced - standard
300 Ohm balanced - optional
Maximum allowable VSWR 1.8:1.0 at full power
Power Source 4160 volts, three phase, three wire, 50/60 Hz (others optional on special order)
Power Factor Better than 0.95
Power Consumption Maximum input power 568 kW at 100% sinewave modulation
Efficiency 65 to 70% at 250 kW carrier power output, depending on the ambient temperature and operating frequency; typically 66% at any modulation depth
Maximum Operating Conditions Altitude - 2,000 feet (600 meters)
Ambient temperature - 10 to 45°C
Relative humidity - 95%
Dimensions: Main cabinet group 7' (2.13 m) H
22' (6.71 m) W
6' (1.83 m) D
Dimensions: Modulator group 7' (2.13 m) H
12' (3.66 m) W
6' (1.83 m) D
Dimensions: Power supply vault
(dependent on building layout)
8' (2.44 m) H
21' (3.66 m) W
14' (4.27 m) D
Weight and volume (packed for export) 38,000 lbs (17,100 kg)
2,800 cubic ft. (79.29 cubic meters)
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
1 4CV250,000C

1 3CW20,000A7


ITU Country
ITU Country