|Table 1: The Marconi B 6128S is the product of evolutionary development|
|B 6124||1975||300 kW||* New RF stage proved
* Frequency preset proved
* Class B modulator
* Solid state control proved
|B 6127||1981||500 kW||* PULSAM PWM modulator
* TH558 RF tube proved
|B 6126 / 6131||1984||300/250 kW||* ADVANCED PULSAM modulator proved
* Frequency follow system proved
* Simplified water cooling system
* Revised modular control circuits proved
|B 6128||1987||500 kW||* Improved B 6126 to allow SSB, (linear and EER) DAM etc||23|
|B 6128S||1993||500 kW||* Derivative of the B 6128 to incorporate all solid state modulator||.|
|Table 2: Proven technology is used in the B 6128S|
|RF stages||Same concept and design as used in Marconi types B 6124, B 6126, B 6127 and B 6128|
|Modulator||Manufactured by Continental Electronics Corp and already fully proven on 500 kW shortwave and 600 kW mediumwave transmitters.|
|Frequency follow system||Circuit design is identical to that used in B 6128|
|Frequency preset system||As used in B 6128|
|Tube and component cooling||As used in B 6128|
|Control circuits||As used in B 6128|
|Power Output||500kW +0.2 dB, -0.4 dB carrier power into a matched 5O ohm unbalanced load or, with external balun, a 300/328 ohm balanced load, at normal supply voltage.
Automatic adjustment of output coupling and tuning is provided to maintain full power into a VSWR not exceeding 2:1 for a 50 ohm load, or 1.8:1 for a 300/328 ohm load.
Automatic reduction of power output to approximately 50% and 25% occurs for load VSWRs of 2:1 and 3:1respectively.
|Types Of Transmission||Amplitude modulation, double sideband (ITU Classification A3).
Amplitude modulation, double sideband, with programme controlled carrier (ITU X3E)
Single sideband, with -6 dB or -12 dB carrier reduction (ITU H3E or R3E) (optional)
|Modulation||High level anode and screen modulation using an all solid state modulator.
SSB modulation is by the Envelope Elimination and Restoration (EER) method.
|Carrier Shift||Less than 5% amplitude between 0 and 100% modulation measured at 1 kHz with constant mains voltage.|
|R.F. Harmonics And Spurious Radiations||The mean power of any spurious r.f. emission at frequencies up to 40 MHz when working into a matched test load will not exceed a value of -70 dB relative to the unmodulated carrier.
For harmonics related to the modulator switching frequency the level will be -80 dB relative to the unmodulated carrier.
For harmonics and spurii above 40 MHz the level will be -80 dB relative to the unmodulated carrier.
|Operating Frequencies||Frequencies within the range 3.90 MHz to 26.1 MHz. Full performance applies to the broadcast bands defined by WARC 1979 as follows:|
|Time For Frequency Change||Not exceeding 30s (typically 12s) for a change between any two frequencies in the range.
This is the time taken for the restoration of programme modulation (at full power, approx. 45s)
|Tuning Method||Pre-selection of up to 4000 frequencies to be stored in a memory, or by frequency following techniques to any frequency in the specified range as determined by the synthesiser. Settings are then automatically stored in the pre-selection memory. A manual tuning facility is also provided.|
|Drive||Synthesiser type, integrated with frequency change system, mounted in the transmitter.
The drive may be demounted and installed in a central area, or capable of frequency selection from a remote point.
Internal frequency reference normally supplied but external 1 MHz standard providing a level of 0.45 to 2.5 V r.m.s. into 50 ohm can be used if required.
|Audio Input Impedance||600 ohm balanced (nominal).
Return loss not less than 20 dB from 50 to 7500 Hz.
|Normal Audio Input level||100% modulation is obtained from a 1 kHz tone at any level from 0 dBm to 15 dBm, by adjustment of a preset control.|
|Audio Frequency Response||±1 dB between 50 Hz and 7500 Hz (A3E)
±1 dB between 100 Hz and 4500 Hz (H3E & R3E) relative to 1 kHz when transmitter modulated to 75%.
|Audio Frequency Harmonic Distortion (A3E)||2.5% at 50% modulation between audio frequencies of 50 Hz and 7500 Hz.|
|Noise and Residual Modulation||At least 56 dB below the level corresponding to 100% modulation by a sine wave signal at 1 kHz.|
|Output Monitoring||R.F. at approximately 2 V peak carrier (at 500 kW) into 50 ohm unbalanced.
A demodulated output provides 0 dBm ±3 dBm (adjustable) into a 600 ohm balanced load at 100% modulation.
|Transmitter Rating||100% sine wave modulation, 60 Hz to 7500 Hz, for 10 minutes per hour, followed by 70% modulation for 50 minutes per hour.
75% sine wave modulation, 60 Hz to 7500 Hz, continuously.
|Incoming Power Supply||Auxiliary circuits:
380 volts or 415 volts (to be specified with order), 3 phase, 4 wire, 50 Hz. Equipment for 60 Hz can be supplied to special order.
Main H.T. Rectifier:
Arranged to suit customer's supply.
Normally 3.3 kV, 4.16 kV or 11 kV, 3 phase.
|Variation of Supply Voltage||Auxiliary circuits: ±10%
Main H.T. Supply:
The transformers are provided with taps in order to compensate for the difference between the normal supply voltage to the transmitter, where this differs from the nominal voltage. Winding are provided so that the phases of the two primaries are offset by ±15°.
The range of adjustment is ±6% in 3% steps. Having selected the correct tap setting the transmitter will remain operational throughout short-term supply voltage variations of ±6% with respect to normal value. In additional full performance (except power output) will be maintained with variations of ±2% of nominal value.
|Variation of Supply Frequency||±4% reference nominal frequency.|
|Overall Power Factor of Equipment||Better than 0.9|
|Auto-restoration||The max period of supply failure for immediate automatic restoration is 15s.|
|Overall Efficiency||71% averaged over the range of frequencies in the broadcast band at 500 kW, when used with cooling equipment optimised for operation at up to 300 m above sea level and at a maximum ambient temperature of 35°C.|
|Equipment Operating Conditions||Ambient temperature
Maximum daily average
Maximum yearly average
Maximum relative humidity
Maximum altitude (ASL)
|1°C to 50°C
2000 m (approx. 6600 ft)
|Equipment Storage Conditions||Ambient temperature (with all cooling fluids drained)
Maximum relative humidity
Maximum altitude (ASL)
|-40°C to 60°C
10000 m (approx. 32500 ft)
|Maximum Dimensions (Excluding heat exchanger and air handling system)
HT Enclosure (typical)
(includes cooling space)
|Specifications may change without notice|
|RF stages||AF stages and modulator|
|1||4CM500,000G or TH558|
|THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES|