14 Aug KWTR goes digital in Pacific through innovation
For many years, KTWR was a station with five 100KW shortwave transmitters. Four of them were Harris SW100s and the fifth one was an HCJB HC100, all five were only capable of analog transmissions. The station has six TCI 611 curtain antennas that allows us to reach the Asia/Pacific Region, an area that includes nearly half of the world’s population.
Since we felt that DRM capability was needed to keep the station viable for decades to come, we bought two used transmitters from Northern Australia in 2010. These transmitters were originally built by Thomson-CSF as model TRE-2326 in 1993. In 2006-2007, these transmitters were converted to TSW-2250D units. They retained their 250KW analog capability, but the ability to transmit in DRM mode up to 150KW was added. The transmitters we bought are essentially hybrids which make maintenance interesting. There are no other TSW-2250Ds on the planet quite like these. Arelis (formerly Thomson) and Ampegon (formerly Thales) do partially support these transmitters with parts and repairs. A fairly unique feature of the 2250D is that it is a single-tube shortwave transmitter that can produce 250KW of output with 77% efficiency. The solid-state driver is rated at 2500W.
Since HCJB was already designing a DRM upgrade kit for the HC100, we acquired a prototype content server from them. It had some initial bugs to be worked out, but it has been working well for a few years now. This will eventually be replaced with a content server that is capable two audio channels. That would allow us to put two programs on the same carrier. When we eventually acquired a Fraunhofer content server as a back-up, we tested its two-channel capability. It was quite nice to see the DRM receiver (DR-111) permitting us to choose the Mandarin or Cantonese program channel. The audio on both channels sounded good. The listeners in Japan seem to enjoy the sound quality.
Even though the TSW-2250D is rated at 150KW in DRM mode, we have not attempted to operate above 120KW. That is a crushing signal for DRM. It is not likely that we would need to operate above 75KW for coverage areas as far away as India. Higher power might be practical if we use a lower-gain antenna for a wider coverage area. We currently use 32KW (the lowest power setting for the TSW-2250D) for Japan.
One reason we like using DRM is that it requires a third of the power consumption when compared to an equivalent effectiveness of an analog broadcast. However, the TSW-2250D is not particularly efficient at its lowest power settings. When the HC100 DRM upgrade is completed, we will probably use the HC100 for our Japanese DRM broadcasts. We might be able to operate at 25KW for that broadcast, but even the 37.5KW setting on the HC100 would save energy compared to what the TSW-2250D uses at 32KW.
We may eventually add another DRM-capable transmitter a few years from now. That depends on how well the transition to DRM goes. We, like everyone else, are awaiting affordable DRM receivers from the manufacturers.
(Item kindly provided by KWTR, Guam)