Digital Radio Mondiale-more power, better reception?
Anthony_UK
Posts: 536 Forum Member
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I think the reason for poor reception on many of the digital radio mondiale test transmissions is ridiculously low power levels because if you dont have decent tx power on shortwave and medium wave for DRM transmissions ie 50kW for Short Wave and 40watts for Medium Wave the service area would be smaller than predicted on medium wave and reception on shortwave would be prone to ionospheric dropouts on occasion.
A bit more power on medium wave DRM transmissions say 100-150watts for a local radio station would extend the coverage zone and 100-150kW on shortwave would improve things quality and receptionwise.
A bit more power on medium wave DRM transmissions say 100-150watts for a local radio station would extend the coverage zone and 100-150kW on shortwave would improve things quality and receptionwise.
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What's the point of increasing power on DRM when very few people are able to receive it?
What the trials demonstrated, among other things, was that you needed tens of low or very low power transmission sites rather than a dozen or so high power sites. This ensures that the field strength doesn't fall below the minimum that'll ensure breakup-free demodulation and decoding. Of course, this was not what broadcasters wanted to hear. While all the trials work was going on, the last of the management layers who knew how to run broadcasting operations with an engineering department retired, very roughly over the time period 1995-2010.
The New Meeja underlings that replaced them at the top grew up in a Cold War- and power cut-free* world of stereo FM. These wanted the institutions to which they drove their VW Beetles each day to be seen as 'publishers' of 'content', outsourcing the messy transmission part to engineering partners. Think along the lines of the R5L promo "...online, on digital, iPhone and tablet...". Any attempt to convince these Bright Young Things that a foray into DRM30 was a good idea was 100% certain to meet with blank stares.
DRM30 missed the boat by about 15 years. Even as late as the mid-nineties, the broadcasters/engineers were still the decision-making layer, and could have gotten behind and pushed the DRM30 concept to give set manufacturers certainty. On the transmission site, they would have been able to channel funds toward re-engineering the MF/LF network for dozens of low power sites working as one or more Single Frequency Networks.
But the reality is that there's zero chance of the above happening. Power levels may or may not have been a contributing factor, as may have been the absence of re-farming the spectrum for 18/20kHz channel that would give high-quality DRM30 some oxygen. The oft-used phrase "technical success but commercial failure" is too simplistic, as the "commercial" bit was never tried. Besides which professional DRM30 systems have been used successfully in the southern hemisphere, for SW audio feeds to remote MW transmission sites. It may also yet have a role in NVIS shortwave systems in tropical regions, where high rainfall plays havoc even with digital satellite systems.
*although stay tuned if it's cold this winter to see where political cowardice in failing to build new nuclear leads us - the predicted power margin is 1.5-2% which is comically insufficient
The Indian DRM receiver launched last September, even though they only showed a prototype, is not yet commercially available, despite promises otherwise and the fact that the production run was 1000 with 800 reserved for All India Radio employees.
One selling point of DRM30 was that it does not require as much power as analogue. But it's just as affected as analogue is by interference and propagation conditions, in fact more so as it drops out completely.