MARCONI B 6133

GENERAL DESCRIPTION


The B6133, 250 kW HF Broadcast Transmitter

photo Marconi B 6133 FEATURES

THE B6133 - HIGH IN BENEFITS, LOW ON COSTS

The premier status of the name Marconi in high power broadcasting is supported with sales of over 650 transmitters in locations around the world since 1960.

The unique design philosophy of the Marconi B6133 250kW Shortwave broadcast transmitter continues this tradition of excellence, achieving the ultimate in operational efficiency, reliability and flexibility with a low capital cost.

The B6133 incorporates the latest technology advances but uses well tried and proven components, many of which are multi-sourced, throughout the design.

It produces either a powerful 250kW of carrier plus 100% modulation, or 375kW of carrier with E-AMC, at all automatically tuned frequencies in the broadcast bands between 5.90 and 26.1 MHz (3.90MHz with optional extension).

The fast automatically tuned frequency change of the B6133 allows for frequency follow band changing in an unequalled time of 12 seconds, after which the transmitter quickly resumes full power output. The facility is complemented with frequency presets in the drive with the ability to store up to 256 settings and the use of sliding RF contacts has been avoided in the high power stages to minimise maintenance and maximise reliability.

A unique Switchable Carrier Control System is provided as standard with the B6133 incorporating:

DAM - Dynamic Amplitude Modulation

AMC - Amplitude Modulation Companding

E-AMC - Enhanced Amplitude Modulation Companding

DAM was the first system in carrier control, but Marconi has incorporated the next generation providing greater efficiency by carrier control techniques known as AMC and E-AMC. AMC typically achieves (dependent upon program i/p) a 30% prime power saving with no audibility degradation. E-AMC achieves the same prime power savings with a higher perceived coverage capability.

The use of an all solid state modulator, using an extremely efficient form of pulse modulation by virtue of the small forward loss and small switching and capacity losses, further enhances the overall efficiency of the B6133 transmitter.

Finally, the compact layout, with easily accessible components, comprehensive fault diagnostics, simple cooling system and installation of the B6132 250kW Shortwave Broadcast transmitter, simply makes the best in the world.

TECHNICAL SPECIFICATIONS
Power Output 250kW minimum carrier power into a matched 50 ohm unbalanced load or, with external balun, a 300 ohm balanced load, at nominal supply voltage.
Automatic adjustment of output coupling 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 ohm load.
Automatic reduction of power output to approximately 50% occurs for load VSWR of greater than 2:1.
Type of Transmission Amplitude modulation, d.s.b. (ITU Classification A3E).
or
Amplitude modulation, double sideband with programme controlled carrier (ITU X3E)
or
Single sideband, with -6dB or -12dB carrier reduction (ITU R3E)
Modulation High level anode and screen modulation using an all solid state modulator
SSB modulation is by the Envelope Elimination and restoration method (EER)
Carrier Shift Less than 5% amplitude between 0 and 95% modulation measured at 400 Hz 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 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 & WARC-92 as follows:
3.90 - 4.00MHz*
4.75 - 5.06MHz*
5.90 - 6.20MHz
7.10 - 7.35MHz
9.40 - 9.90MHz
11.60 - 12.10MHz		 13.57 - 13.87MHz
15.10 - 15.80MHz
17.48 - 17.90MHz
18.90 - 19.02MHz
21.45 - 21.85MHz
25.60 - 26.10MHz
* These frequency ranges are with the optional low frequency extension kit.
Time For Frequency Change Typically 12 seconds for a change to a previously used frequency. The transmitter internal memory will hold up to 4000 previously used frequency settings.
Typical 20 seconds for a change to a new frequency.
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 2.5V r.m.s. into 50 ohms can be used if required.
Frequency Stability
  1. With internal standard 1 part in 108 per day. Less than 1 part in 107 over the temperature range -10°C to +55°C.
  2. With optional high stability internal standard 5 parts in 1010 per day. Less than 1 part in 108 over the temperature range -10°C to +55°C.
  3. With external standard. Will not degrade long term stability characteristics of applied external standard. Standard frequency of 1 MHz at a level of 0.45V to 2.5V r.m.s. into an impedance of 50 ohms unbalanced.
Audio Input Impedance 600 ohms balanced (nominal).
Audio Input Level Control 19.5 dB in 0.5 dB steps by front panel controls.
Nominal Audio Input Level With the front panel control set at centre position, a preset attenuator allows 40% modulation to be obtained from a 400 Hz tone at any level from 5dBm to +l0dBm
Audio Frequency Response ±1 dB between 50 Hz and 6000 Hz
+1,-2 dB between 6000 and 7500 Hz
relative to 400 Hz when transmitter modulated to 75%.
Audio Frequency Harmonic Distortion 2.5% at 50% modulation and 4% at 90% 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 400 Hz.
Output Monitoring R.F. at approximately 10 to 16V peak carrier into 50 ohms unbalanced.
In operation, this feeds the envelope monitor. A demodulated output provides OdBm ±3dBm (adjustable) into a 600 ohms balanced load at 100% modulation.
Equipment Operating Conditions Ambient temperature
Maximum Daily average
Maximum Yearly average
Maximum Humidity
Maximum Altitude		 2°C to 50°C
45°C
35°C
95%
2300m (approx. 7500 ft)
Transmitter Rating 100% sine wave modulation for 10 minutes per hour, followed by 70% modulation for 50 minutes per hour
or
75% sine wave modulation continuously.
Incoming Power Supply Auxiliary circuits:
380 volts or 415 volts, 3 phase, 4 wire, 50 Hz. Equipment for 60 Hz can be supplied to order.
Main H.T. supply:
Arranged to suit customer's supply.
Voltages below 2.4kV not recommended.
Variation of Supply Voltage Auxiliary circuits : ±10% (higher variations to special order)
Main H.T. Supply:
The transformer is 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.
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
Overall Efficiency The measured efficiencies between 3.90 and 26.1 MHz are typically between 75 and 80%.
A carrier shift of 2.5% amplitude at 100% is assumed. Quoted efficiency is based upon power consumption when including all auxiliary power for the transmitter, cabinet air cooling and water circulating pump for an installation with a maximum ambient temperature of 30°C at sea level.
Specifications may change without notice

TUBE COMPLEMENT
RF stages AF stages and modulator
Number Type Number Type
1 4CM500,000G or TH558

1 4CW10,000A



THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES

ITU Country
ITU Country