photo RIZ Transmitters OR 50 K-01/A Short Wave Broadcasting Transmitter type RIZ 50 K-01/A is an automatic tunable amplitude modulated transmitter, capable to operate at any frequency within 3.2 and 26.1 MHz frequency range, with carrier power of 50 kW.

Using Pulse Duration Modulation (PDM) the transmitter provides higher efficiency, lower operating costs and overall performance superior to that of any other standard SW transmitter in the 50 kilowatt power range.

It meets all CCIR requirements for this type of service.

The transmitter itself is constructed as a self-contained unit. It consists of four cabinets designed as rolled-in units. Therefore, it is very suitable for installation in containers for fixed or mobile stations.

All control and monitoring elements are concentrated on the front panel of the transmitter. The transmitter supervision is facilitated by the use of display indicating the equipment status.

The transmitter control and blocking system is designed for easy connection to remote control and supervision circuits.


The 50 kW SW Broadcasting Transmitter type OR 50 K-01/A is a member of the new generation of transmitters with automatic tuning, having the following major characteristics:

* Pulse Duration Modulation

* application of up-to-date technology

* the most modern high efficiency tubes

* convenient and simplified installation

* easy front and rear access

* minimised exploitation and maintenance costs

* reliable operation in extreme climatic and environmental conditions

* automatic tuning

* possibility of remote control and unattended operation.


The transmitter consists basically of four sections, as follows:
AF Chain, RF Chain, Rectifiers and Automatics.


The RF chain is conventional, using only two tubes:
one in the RF3 final stage and
one in the RF2 driver stage, while the RF1 stage is fully transistorized.

RF1 Stage

The RF signal generated in the synthesizer is amplified here, in the transistorized wide-band amplifier, which delivers the RF signal of about 100W into 50 Ohm.

RF2 - Driver Stage

In this stage an air-cooled tetrode type RS1072CL is used to amplify signals from the wide band amplifier to the level necessary for driving the final stage.

Coupling to the final stage is accomplished by a P1-filter tunable by variable capacitors and coils.

RF3 - Final Stage

The newest type of tube, tetrode RS 2054 SK with graphite grids structure cooled by the vapour condensation, is used in this stage as a Class C power amplifier.

Output power is via coupling capacitor and double P1-filter transferred from the tube plate to the coaxial output of the transmitter. Necessary attenuation of harmonics is achieved by passing via harmonic filter.


The AF chain is unconventional because PDM technique is used. It consists of three main stages:

AF1 Stage

This stage transforms the AF input signal into a square wave signal, with duration in accordance with amplitude of the AF input signal.

It also contains circuits for correction of amplitude and phase characteristics and for adjustement of negative feedback.

The square wave pulses with correct shape and duration obtained, are led via an optical cable to the input of AF2 stage.

AF2 - Driver Stage

This stage is equipped with two small aircooled tetrodes RS 1072C controlled by a transistorized switching amplifier.

AF3 - Final Stage

It consists of the tetrode RS 2054 SK operating in switch mode and the filter which delivers average anode voltage of 8 kV necessary for RF final stage tube.

During the modulation process anode voltage varies (8 ±8 kV; m=1) in accordance with AF input signal amplitude.

It is placed in the AF cabinet of the transmitter.


After the setting of the required transmitter operating frequency on the synthesizer, the automatic transmitter tuning system allows automatic tuning of the transmitter final power stage to required frequency.

Tuning action is carried out in two steps:

After the appropriate fine tuning elements are brought into required positions the motors are locked and the transmitter is ready for modulation.

The transmitter is automatically tuned in max 60 seconds.


This system automatically controls the correct sequence for switching the transmitter ON/OFF.

It checks critical parameters of the operating characteristics of the transmitter, reacting in the appropriate way to:

The protection system is equipped with a recycling and lock-out unit (integrator) which counts the "short interruptions", and if their number reaches three within the time period of 20 seconds, it regards the failure to be permanent and switches the transmitter off.


Power supply consists of three parts:

The high-voltage rectifier is designed as a three-phase full-wave rectifier of semiconductor type, and delivers anode voltage for the AF final stage.

Auxiliary rectifiers used in the transmitter for DC supplies are of semiconductor type and full-wave configuration.

Auxiliary rectifiers for the AF chain must be supplied via an HT insulated mains transformer.

All rectified voltages are filtered by means of filter capacitors and chokes.

In this stage stabilized voltages for the tube filaments are also generated.


Normal Operation
The transmitter is designed for continuous 24-hour operation with an average modulation depth of approximatively 60% and peaks up to m=100%.

The transmitter can withstand, without damage, a short duration of AF input signals fm=1 kHz, 6 dB above the level required for 100% modulation.

24-Hour Test Operation
The transmitter is designed for 24-hour test operation as follows:
100% modulation depth with a sinusoidal signal, frequency 1 kHz, for duration of 10 minutes, after that, with 60% of average programme modulation depth for a duration of 50 minutes, and so on within 24 hours.

Stability of Technical Data
The technical data stated in this specification are guaranteed for mains voltage tolerance between +5% to -10%, with the exception of RF output power, consumed power, efficiency, and carrier shift.

Change of Operating Frequency
Necessary frequency changes are executed automatically within less than 60 seconds.

Power Supply
Mains voltage 3 x 380V / 220V, +5%, -10%
Power input (fm=1kHz/m=1) 150 kVA
Mains frequency 50 Hz or 60 Hz ±5%
Power factor cos phi greater than 0,9
Modulator Input
Input impedance (from 60 to 7500 Hz) 2000 Ohms balanced standard,
600 Ohms balanced as option
Input level (for fm=1 kHz, m=1)
(0 dBm=0.775V across 600 Ohms)
-4 to +10 dBm
Transmitter Output
RF output load impedance 50 Ohms unbalanced, 60 Ohms unbalanced as option
Permissible VSWR s less than 2
Climatic Conditions
Temperature in transmitter hall +5 to +45 C
Max. altitude above sea level 2300 m
Relative humidity less than 90%
RF Output Power
Carrier power in the range 3.2 to 26.1 MHz 50 kW
RF Exciter
Frequency synthesizer 3.2 to 26.1 MHz
Frequency stability 2 x 10-7 per day
Modulation System
Type of modulation High level amplitude modulation
Modulation principle Pulse Duration Modulation
Type of emission 9A3, 15A3 as option
Modulation Characteristics
The ratio of input to output as function of modulation depth up to m=80% does not differ by more than ±0.5 dB
Signal to Noise Ratio
Unweighted more than 50 dB
Weighted more than 60 dB
Reference level m=100% fm=1 kHz,sinusoidal
Mains voltage sinusoidal
Spurious Emission
Mean power of any spurious emission supplied to the antenna transmission line below the mean power of the fundamental more than 60 dB
Carrier Shift
Carrier shift at m=90% with fm=1 kHz sinusoidal and
at a constant mains voltage referred to the unmodulated carrier
less than 4%
Overall Efficiency
Modulation depth 0% 30% 100% (fm=1 kHz, sinusoidal)
Overall efficiency 60%
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
1 RS 2054 SK 1 RS 2054 SK
1 RS 1072 C 2 RS 1072 C


ITU Country
ITU Country