transmission special report Many broadcast facility operators
are finding that the cost of purchasing and operating air conditioning systems is increasing. The typical air conditioning unit requires ongoing maintenance and eventual replacement on a five to eight year cycle. The combined operating, maintenance, and replacement costs become a significant part of the overall facility operating cost. Liquid cooled transmitters have
significantly lower energy consumption than the combined energy consumption of an air cooled transmitter and the required air conditioning.
Transmitter efficiency optimisation
Several recent technology advancements have significantly improved transmitter operating efficiency. The introduction of 50V LDMOS RF transistors has made a significant improvement in transmitter power amplifier operating efficiency. Figure 1 shows a comparison of three different MOSFET technologies currently used in broadcast transmitters. Figure 2 shows improved efficiency and power gain of the latest
generation 50V LDMOS RF transistors. 50V LDMOS technology offers higher
amplifier gains of 19dB in digital DVB-T operation and 21dB in FM operation, thereby reducing the inefficiency of the drive stages. Typical DC to RF efficiency of over 28% in DVB-T operation and 84% in FM operation can be achieved. The latest generation switching
power supplies have significantly improved the conversion efficiency from the AC mains input power to the DC power required by the LDMOS RF transistors.
Typical power supply
conversion efficiencies have improved from 85% to 95%. Switching power supplies have also eliminated the need for outboard voltage regulators with their associated operating, cooling, and maintenance costs. Switching power supplies make it possible to use either polyphase or single phase AC power sources. Remote transmission facility locations where polyphase power is not available can eliminate the cost of bringing polyphase power to the facility or the costs of converting single phase power to polyphase power. Advanced signal processing enables
both Real Time Adaptive Correction (RTAC) and Advanced Crest Factor Reduction (ACFR) that allow the RF
Figure 2: 50V LDMOS efficiency and gain.
power amplifiers to operate more efficiently closer to saturation than previously possible. Regardless of whether an air
cooling system is used or a liquid cooling system is used, the energy consumption of the cooling system can be significantly reduced by carefully matching the system capacity to the ambient conditions. Variable speed cooling systems adaptively utilise thermal feedback to consume only as much energy as required for the current temperature and heat load. There may be a small benefit to
sharing a common air conditioning system across several transmitters,
www.ibeweb.com l september/october 2012 l ibe l 75
Continued on Page 76.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84