AM radio beats a smartphone any day
By Nigel Holmes - posted . See all Nigel Holmes's articles
It turns out that smartphones aren't a good bet for the future of radio transmission; and there are particular benefits to AM radio.
He might have said "Bandwidth ain't bandwidth".
Radiated, assigned bandwidth (the kind that comes out of the mobile phone towers) isn't the same as conducted, directed bandwidth (i.e that carried on copper or fibre).
This is what killed "Broadband-over-Powerline" - the limited infrastructure couldn't match the increasing needs of the users.
The limiting infrastructure characteristic for mobile customers is the amount of UHF (around 1,000-4,000 MHz) carrier bandwidth available to each telco to service mobile platforms. It is finite and shared between competing telcos in a given market.
What most broadcasters totally don't get is that a typical AM station in Australia, 3AW, occupies 20 kHz of bandwidth. But that 20 kHz pipe can reach 24,000 million bazillion users simultaneously. It doesn't matter if if they're fixed or moving at Mach 2.
Put the same audio on a data stream carried by UHF into a mobile platform and the data rate is a paltry 6-7 kbits/s ... per mobile handset. Mobiles don't receive a broadcast in the same way as your 1940's wireless set. And the 3AW data stream must share carrier bandwidth with the myriad interweb offerings to the mobile platforms.
Mobiles connect to the cell network individually, and are subsequently addressed as separate entities. Telcos will always be delighted to relieve you of disposable income, but only up to the extent they can squirt data to a finite number of handsets per chunk of UHF. Who gets pissed off first with this arrangement remains to be seen. I'm betting on the consumer.
Standard cell & spectrum planning techniques help - as does 4G - but they don't overcome the intrinsic limitation of radiated, assigned bandwidth.
This is particularly relevant in an emergency. Only if I worked in the funeral business would I say: “by all means rely on your smartphone during an emergency”.
During Victoria’s 2009 bushfires when 173 souls were lost, 40-odd mobile cell stations were obliterated. Others nearby were overwhelmed with calls from the doomed, the curious & the wilful.
Mountain-tops were incinerated (guess where FM/TV/DAB+ transmitters live). The mainstays of emergency broadcasts were the 50 kW public broadcaster on AM (774 kHz) and the leading commercial broadcaster in Melbourne on 693 kHz with 5 kW.
Both stations operated from large, cleared sites with secured power & comms links. Both stations had tremendous regional coverage even to mobile receivers.
Our emergency agencies’ websites crashed under the demand (again: the doomed, the curious & the wilful). Delays in updating the sites with accurate information didn’t help.
One of the first effects of bushfire is loss of mains power, either intentional or consequential. Either way it’s hard cheese if you have a landline phone or web access that needs mains. Or a smartphone with a flat battery.
In Victoria emergency agencies (CFA & SES), the state government and the survivors of previous fires & floods advise the use of a battery-powered portable mf radio kept in good working order. At good volume my 25-yo GE Super Radio draws ~50mA from D-cells. I let it run continuously for nearly a week before I got bored with the exercise. It lasted several more months in intermittant service. Try that with a smartphone.
Across Victoria (240,000 sq km pop. 5.5 million) there are four AM transmitters with proven coverage and proven availability. We have large signs along main roads giving emergency advice “tune to 774 kHz”, “tune to 828 kHz”, “tune to 594 kHz” and “tune to 756 kHz”.
Relying on a smartphone during an emergency is a silly thing to do. AM radio - maligned though it is in some quarters - still has much to offer.
This article was edited from emails and discussion postings to Media UK.
Nigel Holmes is Chief Engineer for Radio Australia. He writes here in a personal capacity.
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Nigel – you shouldn’t really talk about “an amount of UHF”.
In any case – UHF is defined as 300 to 1000MHz.
2G, 3G and some of 4G are above that – in SHF – 1000 to 3000 MHz.
Hello Ian. Thanks for the comment. I did note “1000 – 4000 MHz” & I didn’t want to be too pedantic – otherwise I’d have written UHF/SHF because UHF is 300-3000 & SHF is 3000-30,000 MHz.