|Power output||250 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|
|Power output variation||Automatic reduction of power output to approximately 50% or 25% for load VSWR's up to 3:1 and 4:1 respectively|
|Operating frequencies||Frequencies within the range 3.95 MHz to 26.1 MHz.
Full performance applies to the broadcast bands defined by WARC 1979 as follows :
|Time for frequency change||Not exceeding 10s for a change within the same band.
Not exceeding 35s for a change from one band to another.
Typical frequency change time 20s.
|Tuning method||By frequency following techniques to any frequency in the specified range as determined by the synthesiser. A manual tuning facility is also provided.|
|Type of transmission||Amplitude modulation, d.s.b (CCIR Classification A3)|
|Modulation||High level anode and screen modulation using the Advanced Pulsam PWM modulation system.|
|R.F output load impedance||50 ohm unbalanced, max V.S.W.R 2:1 or 300 ohm balanced, 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.
|R.F load variation||Automatic adjustment of output coupling and tuning is provided to maintain full power into a mismatch not exceeding 2:1 for a 50 ohm load, or 1.8:1 for a 300/328 ohm load.|
|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 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, 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.
|Carrier shift||Less than 5% amplitude between 0 and 100% modulation measured at 400 Hz with constant mains voltage.|
|Audio input impedance||600 ohm 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 -5 dBm to +10 dBm|
|Audio frequency response||±1 dB, 50 Hz and 6000 Hz +1 -2 dB between 6000 and 7500 Hz relative to 400 Hz when transmitter modulated at 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 400 Hz.|
|Output Monitoring||R.F at approximately 10 to 16 V peak carrier into 50 ohm unbalanced. In operation, this feeds the envelope monitor. A demodulated output provides 0 dBm ±3 dBm (adjustable) into a 600 ohm balanced load at 100% modulation.|
|Equipment operating conditions||Ambient temperature : 2° to 50°C max.
Daily average 45°C
Yearly average 35°C
Maximum Altitude : 2300 m (approx. 7500 ft)
Maximum Humidity : 95%
|Transmitter rating||100% sine wave modulation for 10 mins per hour, followed by 70% modulation for 50 mins. per hour OR 75% sine wave modulation continuous.|
|Incoming power supply||Auxiliary circuits : 380 V or 415 V 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 or 11 kV 3 phase.
|Variation of supply voltage||Auxiliary circuits : ±10%
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.
The range of adjustments 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 the 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.|
|Overall power consumption and efficiency||
Power Output (kW)
Power Input (kW)
Overall Effy %
|A carrier shift of 2.5% amplitude at 100% is assumed|
|Specifications may change without notice|
|RF stages||AF stages and modulator|
|1||4CM300,000GA or TH537||1||TH555|
|THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES|