Is the future for AM radio a switch to digital?
29 April 2019 · Features · News · Radio Tomorrow with James Cridland
Radio Tomorrow with James Cridland
If radio’s audience is getting progressively older, AM radio is partly to blame: in most parts of the world, AM radio is the home of shouty and reactionary tal...
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What is the principle of operation of operation of AM HD radio? Can it co-exist with the same station's analogue signal on the same carrier frequency? Does the 'Q' of an existing station's antenna system generally need to be modified to accommodate the digital signal?
The days of AM-stereo returning as the medium of choice are non-existent. The reason why AM has the reputation of poor sound quality is that most of the radios where equipped with a narrow IF bandwidth, typically 7kHz (3.5kHz per sideband), whether the radio was mono or stereo. There were radios with an audio bandwidth of 10kHz (20kHz total bandwidth) plus such as the Sony STJX220A or the Australian-made Audiosound radio.
When one heard a wideband AM stereo signal, the quality rivalled the FM stations especially on 2SM between 1985 and 1998 and 2GB between 1985 and 1994. Unfortunately most people would have been unaware of the potential of AM radio. On top of that the benefit of the CQUAM system was that the bandwidth was the same as a mono station.
Despite the potential of AM's sound quality rivalling FM, the public still had the perception that AM sounded poor because the majority of radios had a narrow bandwidth. AM stereo is passe.
DAB in Australia is the great leveller with both AM and FM stations simulcasting on DAB and then some.
The question remains, given that DAB is established in the capital cities, is it economically feasible to have one or two other digital systems such as DRM (Digital Radio Mondiale, not Digital Rights Management) and HD-Radio?
Both offer 'FM' quality sound, they can be broadcast on any frequency band and additional data services can be transmitted. For HD-Radio, the established analogue signal can be transmitted with car radios automatically switching between the analogue and digital service.
When broadcasting on the MW and SW bands, the digital signal can be propagated over long distances as the analogue signals on the MW and SW bands.
DAB is well established in the capital cities. While DAB/FM/AM radios are available such as Sangean's DPR-45 and DPR-44 ('Dick Smith'-branded Sangean) or Bush's BR30DABAM, these are rare. It would be questionable whether people would like to have another DRM or HD-Radio?
It appears that DAB+ is the established standard in Australia with plans to rollout DAB+ in regional areas, source https://www.acma.gov.au/Industry/Broadcast/Spectrum-for-broadcasting/Broadcast-planning/digital-radio-1#q13 and it appears that DRM is unlikely to be implemented in Australia, https://www.acma.gov.au/Industry/Broadcast/Spectrum-for-broadcasting/Broadcast-planning/digital-radio-1 under the heading "What digital radio standard is used?"
In sum, DAB is the established digital broadcasting standard in Australia. It is unlikely that HD-Radio and DRM will ever be implemented.
Regards
Anthony of exciting Belfield
Ethelred,
Thanks for your question.
The principle of AM HD radio (as used in America) is to provide a transition to digital transmission solution for American radio. The way it is currently used is to broadcast AM (at lesser power) and digital HD from the same transmission and antenna equipment on the same frequency. The long term aim is to shut off AM so that the full bandwidth and capacity of digital can be used.
The other digital AM system, DRM (which also works on FM and SW) has similar aims and technology but uses a different encoding and transmission system.
DAB+, the system used in Australia, is not used this way, it transmits on different frequencies and is an additional and/or replacement system which uses all the digital capacity to deliver more benefits than when HD and DRM are used in conjunction with AM.
EDITOR
To Ethelred - thanks for the comment.
You *can* run AM "HD Radio" in a hybrid mode, which co-exists with the same station's analogue signal. This is fine and works well; but the digital signal is necessarily rather weaker than the analogue signal - and it only works in countries with 10kHz spacing, rather than Australia's 9kHz.
What's happening here is that the FCC have allowed this one station to try an all-digital signal, with no analogue component. This means that instead of 10% of the power going on the digital signal, it's much, much stronger - so coverage is far more robust.
I don't know enough to answer the second question.
My column goes to the US as well as Australia - so let me take this opportunity to add that the US won't let you use DRM on the MW band. In any case, with 20% of cars having HD Radio inside them, it would be foolish to switch to DRM for MW. However, here in Australia, exactly 0% of cars have HD Radio inside them - so if we're to try digital AM, we should be using DRM. That a) works at 9kHz; b) is in use on MW in India (though nowhere else at any scale); c) is closely related to DAB+ and therefore a DAB+ and DRM set should be easy and cheap to build.
DAB+ is great for metro areas, where its prime use is to add significant additional choice. However, in the bush, DAB+ is not the correct choice. Unlike Europe, Australia should probably look at a hybrid approach, with DAB+ for cities and towns, and DRM to replace analogue AM. Otherwise, the bush will be without any viable form of radio, in my humble opinion.
A lot of people under the age of 50 still listen to AM radio, despite the ratings.
As someone who travels regional areas a lot, I have seen the extraordinary range a AM station with just 5 kW (5000 watts) of power can achieve. On the flipside, I've also seen the coverage area a 200 kW station on FM can achieve.
There are 4 elephants in the room when discussing the future of AM broadcasting in Australia:
1) The short range of DAB+ (less than 30km) means it can never truly be a competitor to AM radio (or even FM radio) in regional areas
2) Emergency situations - mobile phone towers are the first to go due to planned (or forced) power outages so streaming is out, and the large power requirements of DAB+ means it's much less attractive than AM/FM radios which can be powered for months on one set of batteries (even more recent models with digital displays). Every bushfire or flood survival kit needs a battery powered radio - a message that is drilled into all of us through frequent ads.
3) The nature of DAB+ in Australia where only commercial networks (who are useless in emergency situations by the way) ensured that community and narrowcast broadcasters were pushed out and the large number of DAB+ stations owned by just a handful of operators. Some community stations are allowed on DAB+ but in Adelaide there is one commercial broadcaster not on it, and multiple community stations left out. Part of the problem is technical where not enough bandwidth was allocated to DAB+ in Australia - that's an issue for the ACMA but no doubt commercial radio australia had a hand in that as well
4) Broadcast Australia - the company that broadcasts your ABC around the country often gives laughably tiny power levels to it's FM transmitters, especially new ones. The ABC repeater in Augusta WA is a great example of this. With it's puny 60 watts of power it can't even reach the town's caravan park (which is within 5 minutes walk of the main street).
BA could consolidate a number of small transmitters into one very large transmitter and provide greater reach on FM than DAB+ could ever hope to provide. The FM transmitter at Mildura/Albury/Wadonga covers a very large area (over 200kms driving distance between towns).
How are you going to provide coverage of local and commercial radio for travellers on the highways of the NT or WA or QLD if you kill off AM? One way is to build some very large (200 to 500 kw, even 1 million watt transmitters exist in Europe) transmitters every 300km or so. Another way is to build mobile towers every 50km.
However with DRM you can cover even more area with less power. Stations in India, Russia and other parts of the world are rolling out DRM covering some very large areas with just one transmitter.
Either way the solution is not DAB
It's a shame we didn't adopt the HD+ standard of the USA, however DX (distance) reception over HD+ is difficult as it's still in a state of coexistence.
During many natural disasters in the USA, I'm sure some younger people were reaching for AM radio for news and information.
Listeners are attracted to AM radio for the content, the platform of listening is not so important to them so long as they can access the stations they want, using the devices they choose.
DAB+ is a superior format to both HD Radio and DRM and a better choice for consumers because it’s well-established globally and thus there’s greater range and availability of affordable receivers.
The number of car manufacturers supporting DAB+ is not matched by HD and certainly not by DRM. The difficulty of a hybrid model involving two systems is that there are no multi standard receivers.