|Power output||500 kW, +0.2 dB, -0.4 dB into a matched 50 ohm unbalanced load, or a 300 ohm balanced load with external balun, at nominal mains voltages.|
|RF output load impedance||Full power is delivered into a 50 ohm or 75 ohm unbalanced load max. v.s.w.r 2:1, or 300 ohm balanced load, max. v.s.w.r 1.8:1 using the external balun.
The balun can be designed for an impedance of 328 ohm for special cases.
|Power output variation||Full power up to 2:1 v.s.w.r (or 1.8:1 at balun output). Automatic reduction power output to approximately 50% or 25% for load v.s.w.r's up to 3:1 and 4:1 respectively.
In A3E mode, operation at half and quarter power is possible, selected by remote control, or locally.
|Operating frequencies||Any frequency, in 100 Hz increments, 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||For autotune : Not exceeding 30s (typically 20s) for a change from any two frequencies inthe specified range, this time is taken to 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.|
|Type of transmission||Amplitude modulation, double sideband (ITU Classification A3E)
Amplitude modulation, double sideband, with programme controlled carrier (ITU X3E)
Single sideband, with -6dB or -12 dB carrier reduction (ITU H3E or R3E).
|Modulation||High level anode and screen modulation using the advanced Pulsam pulse width modulation system for A3E. SSB modulation is by the Envelope Elimination and Restoration (EER) method.|
|RF harmonics and spurious radiations||The mean power ot any spurious rf 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 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.
|Drive||Synthesiser type, integrated with the frequency change system, mounted in the transmitter. The drive may be demounted and installed in a central area, and is capable ot frequency selection trom 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. unbalanced can be used if required.|
|Carrier shift||Less than 5% amplitude between 0 and 100% modulation measured at 1 kHz with constant mains voltage.|
|Audio input impedance||600 ohm balanced (nominal). Return loss >20dB from 50 to 7500 Hz.|
|Nominal audio input level||100% modulation is obtained from a 1 kHz tone at any level from O dBm to 15 dBm, by adjustment of a preset control.|
|Audio frequency response||±1 dB between 50-Hz and 6000 Hz +1, -2 dB between 6000 Hz and 7500Hz relative to 1 kHz when transmitter modulated to 75%.|
|Audio frequency Harmonic Distortion||2.5% at 50% modulation and 4% at 90% modulation between 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||RF at approximately 2 V peak carrier (at 500 kW) into 50 ohm unbalanced. A demodulated output provides O 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 min per hour, followed by 70% modulation for 50 min per hour.
75% sine-wave modulation, 60 Hz to 7500 Hz, continuously.
|Incoming power supply||Auxiliary circuits : 380 V or 415 V (to be specified with order) three phase, 4 wire, 50 Hz (Equipment for 60 Hz can be supplied to special order).
Main HT rectifier : Arranged to suit customer's supply. Normally 3.3 kV or 11 kV three phase.
|Variation of supply voltage||Auxiliary circuits : ±10%
Main HT 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.
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 addition 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||65% averaged over the range of frequencies in the broadcast bands at 500 kW, when used with cooling equipment optimised for operation at up to 300m above sea level and at a max ambient temp. of 35°C.|
Ambient temperature: 1° to +50°C max.
Average temperature over any 24 hour period not to exceed 45°C and, over one year, not to exceed 30°C.
Maximum Altitude : 2300m (approx. 7500 ft) above sea level.
Maximum relative Humidity : 95%.
Storage and Transport:
Ambient temperature range, with all cooling fluids drained, -40°C to +60°C.
Maximum altitude: 10000 m (approx. 32500 ft.) above sea level.
Maximum relative Humidity: 95%.
|Maximum dimensions||(excluding heat exchanger and air handling system):|
|Specifications may change without notice|
|RF stages||AF stages and modulator|
|1||4CM500,000G or TH558||1||4CM300,000GA or TH537|
|THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES|