The Future of Medium Wave DXing in a Digital World
by Paul Ormandy on 24-08-2004
Digital
broadcasting on mediumwave is almost here! Widespread implementation will
begin in 2003 and while we can speculate about the ‘bells and whistles’ that
digital will bring and whether DXing as we know it will survive, how will we
fair in the short term, DXing analogue signals in the midst of the digital
revolution?
For years now the news for New Zealand MW DXers hasn’t been good, which is a reflection of the scene globally though with its own ‘Kiwi” twist. More and more stations entering the market (which seemed saturated as it was), 24-hour broadcasting by all and sundry and national networks setting up stations in every city. These factors along with the advent of ‘Access Radio’ stations offering an outlet to minority interest groups has resulted in a plethora of stations inundating the MW band. And that’s without taking the high noise levels besieging urban DXers into question!
The opening of the FM band in New Zealand two decades ago, and the hoped for mass exodus of MW stations to VHF with the resultant gaps in the broadcast band never materialised. Existing AMers simply simulcasted or ran alternate programming on each band, (despite the government's intentions that any station wanting to move to FM had to relinquish its AM channel) doing little to improve the lot of the MW DXer.
The only good news for New Zealand MW DXers in recent times was that our government would not allocate channels in the extended band (1602 – 1701kHz) thus leaving it free for DXing foreign stations (and it has been a great source of renewed interest in MW DXing too).
So, what will be the impact of digital broadcasting when endeavouring to DX analogue signals in a dual-mode environment, and will our hobby survive in an all-digital world? It is possible that initially digital broadcasting may allow for better reception of analogue signals. The faintest suggestion that things may improve for the medium wave DXer will arouse my interest.
The Implications for DXers
Let’s look at the factors that make life more difficult for us diehard MW DXers and speculate as to what might happen…
Interference
Digital signals will have a tighter bandwidth, so
their signals will not cause as much adjacent channel interference
(“splash”) as existing AM broadcasts. As an example, if an analogue signal
wipes out reception on channels 20kHz either side of its nominal frequency,
a digital signal may only wipe out channels 5kHz either side. What’s more,
the level of splash from an AM signal varies with modulation (and there are
some forms of audio which cause more splash than others, notably applause
and bagpipes!). Digital signals will not vary in modulation so levels of
splash will be constant (not sure whether that’s good or bad!).
While a digital receiver will be clever enough to discriminate between co -channel analogue and digital modes (and even co-channel and adjacent channel digital signals thus rendering interference a thing of the past), reception of the two mixed-mode signals on an analogue-only receiver will produce a new form of QRM to deal with. Top-end “dual mode” receivers may allow reception of both at good levels by toggling between the two modes.
Congestion
The narrower band space occupied by digital
signals will also increase the number of channels available to broadcasters
without extending the existing band. In countries where channels are
clogged, like in the USA where there are 4,000 plus stations sharing the
available 117 frequencies, restrictions (limited hours and low-power
operation) imposed on a non-interference basis could be relaxed which would
free up more channels to be occupied.
The current spacing between channels in cities is around 30kHz. So over the band (530 – 1700kHz) there are 39 channels at 30kHz spacings. If 20kHz is a suitable spacing for digital signals, then 58 channels would become available. So another 19 stations could be accommodated… and the implications increase if 10kHz is a suitable spacing. Not only would this mean more local and semi-local stations, it would also have the effect of narrowing the potential gap for DXing stations, which may not be good news for listeners living in those environments.
Then what if it was possible to transmit several program streams at once over the same transmitter? That could lead to de-congestion as several stations owned by one company servicing the same area could all broadcast over just one sender. Thus saving on transmitter running and replacement costs and capital outlay. We could also have companies in the business of owning transmitters leasing available channel-space to broadcasters, even the streaming audio ‘stations’ currently proliferating on the Internet!
A Move from FM back to MW?
For
the last 2 decades, the attraction of the superior audio quality of FM has
often seen stations sacrificing the coverage of AM to obtain the better
dynamic range and frequency response that FM offers. Many new stations have
gone straight to FM and given MW little consideration. Also, it’s generally
cheaper to establish an FM station from an aerial point-of-view… no large
tract of land is required to place a tower and radials upon as an FM aerial
needs to be little bigger than an average VHF TV aerial.
And the programming has been split too, with most music stations on FM and talk stations on MW.
If the audio quality of digital is as good as FM, then
stations may opt
to use MW to increase coverage while retaining audio
quality. This could lead to MW once again becoming a multi-format mode with
high-quality music channels alongside the ‘talkers’.
At some stage, once receiver penetration into homes
reaches a crucial point and digital AM broadcasters begin to figure in
listener polls, the increased audio quality and coverage on MW will be used
as a tool to entice advertisers to use MW instead of FM. Competitors eager
to retain their advertising clientele will create a certain synergy, leading
to an explosion of digital MW stations as existing AM stations convert and
FM broadcasters switch to the new mode.
All of this could lead to congestion on a scale never imagined, and until we know how “DXable” digital signals will be, we won’t know the shape of MW DXing in the future.
Being totally pessimistic, (which is not my nature) the death knell of MW DX may be ringing as this new technology threatens. Being optimistic, there may be increased opportunities before digital gains real momentum, with the narrower bandwidth, less splash and slow conversion by many, particularly Third World nations to the new mode.
