Saving AM: Time for Radical Change?
The author is technical editor of Radio World Engineering Extra.
© Ildar Sagdejev / Wikimedia Commons / CC-BY-SA-3.0
I’m encouraged by the recent groundswell of
concern for the AM radio band. Every year seems to make the operating
conditions for AM stations a little worse. Each year the land required for an
AM directional antenna field gets more expensive to acquire or maintain. Each
year electromagnetic noise grows a bit more, especially in desirable urban
areas. Each year it seems the receivers get worse. Every year the cost of
electricity gets a bit higher while the reliable coverage area shrinks. Every
year it seems fewer people take AM seriously, as owners, listeners and radio
suppliers. New portable electronic devices that sometimes feature FM radios
rarely, if ever, offer AM tuners.
NOT WISELY BUT TOO WELL
The problems of AM can only be
described as structural and fundamental to the band itself. Key to today’s
challenges are the overly optimistic allocation policies of the post-World War
II FCC in its mission to bring radio to everyone.
In the process, stations were created that were crippled from
the beginning: daytime-only or so completely interference-limited that service
could only be expected to carry about 8 miles at best. As if this wasn’t
enough, the widespread use of very expensive and complex directional arrays
created a tier of stations that could scarcely afford to operate, let alone
legally maintain their limited patterns. Everyone knows a painful example of
one of those.
This “allocate at all costs” approach
worked until real competition came along with the growth of FM. Today it is
hard not to see the underlying flaws of creating a system that mixed a few very
powerful stations with thousands of severely limited signals in a hierarchy
that worked only for the largest players.
THE INTERFERENCE SPIRAL
Then there were the attempts to increase audio bandwidth to
compete with FM. This virtually guaranteed that stations would interfere with
their first- and second-adjacent neighbors, again due to a defective allocation
scheme that placed stations within 5 and 10 kHz of their neighbors.
The adoption of the first
bandwidth limiting NRSC standard in 1988 further demonstrated that AM is often
its own worst enemy, with stations now encouraged to use vicious amounts of
pre-emphasis as long as they complied with an overall bandwidth limit of 10
kHz. Radio manufacturers countered with ever-reduced quality in AM radios,
noting that listeners dislike interference more than they wanted high-frequency
response. Subsequent revisions to the NRSC, including the recent NRSC-2-B in
September of 2012, have tried to refine and improve the bandwidth mask in the
hope that it will encourage receiver manufacturers to make better receivers.
Interestingly, a simultaneous standard, NRSC-G100-A,
began finally to address the problem of encouraging structural interference by
exploring the quality improvements that could be met by limiting bandwidths
below 10 kHz. Unfortunately I haven’t yet
seen the discussion move to what is an obvious solution: Get rid of the
pre-emphasis curves and remove all that extra energy from exactly where it does
the most interference damage, right on top of adjacent stations. At least the
conversation is proceeding in a rational direction with the realization that
all you are going to get is 2–3 kHz of audio bandwidth unless AM stations
themselves stop creating all this unnecessary interference. A frequency
response of 5–7 kHz can actually sound quite good. It’s sad to observe that it
has taken nearly 25 years to see the first inkling of this understanding.
Meanwhile AM radios remain uniformly dismal.
STILL IN DEMAND
If AM is so fundamentally flawed, why try to save it at
reasonable question and sometimes it feels as if we have reached a de facto
consensus to just let AM crumble away and die from neglect.
Personally, having grown up listening to AM radio in the 1960s, and having
worked for many years at AM stations, I feel there is still something there
worth keeping. One advantage of good AM is that all it requires is a simple and
inexpensive tuner and transmitter design. This makes it a perfect free consumer
technology. AM offers advantages in coverage compared to FM when it isn’t so
severely interference limited. There’s no multipath or terrain shielding.
And there are still so many voices that strive for broadcast
coverage, as witnessed by the number of applicants for new licenses that occur
at every FCC window. Why not keep AM alive to serve the many that want to
become broadcasters but don’t have the money to compete for FM licenses with
huge corporations like Clear Channel or Cumulus?
Given the number of structural problems
faced by the AM band, perhaps it’s time to consider more radical solutions than
we’ve seen in the last 25 years.
I recall 20 years ago
it was sometimes joked that the way to fix AM was to eliminate all daytimers,
DAs with more than two towers and stations with less than 5,000 watts. Perhaps
there is truth in that old chestnut, and the only way forward is to come up
with a method to reduce the structural defects of too many allocations. The
trick is to come up with the method of doing so that shares the pain and the
cost amongst the winners. I’m guessing the FCC would be open to just about any
approach and might be able to offer some incentives.
While we’re at it, is there really a justification
for the remains of clear-channel allocations clogging up the band? Regional
service is pretty neat, especially in the wide open parts of the country. But
in densely populated areas allocating just a few stations with signals that
reach many millions delivers a solid benefit to just a small group of owners.
Those owners are especially motivated to keep AM profitable, but if AM
disappears they will suffer with the rest. Some might say these stations are
the only ones with the resources to save AM.
work remains to be done to improve receiver bandwidth. If there are fewer
allocations this will be easier. Digital AM has some promise in the long run,
though it has been criticized by many as a cause of even more interference to
the existing allocation scheme.
I also like the
ideas proposed by Ron Rackley and Ben Dawson recently in the pages of RW (see www.radioworld.com/freshlook).
For example, if we eliminate the minimum efficiency and ground system
requirements for AM antennas, it would make it far simpler to “repack” the AM
band in such a way that separations can be increased in a meaningful way.
Currently this is impossible; the technical standards meant to maintain AM
“quality” are a lead weight clamped on a lifeline. It would also greatly reduce
the cost of operating AMs in terms of land and local regulatory burdens.
We should take a page from the DTV band repacking and see what
would happen if we actually started to eliminate some channels and move the
others around with the antenna burdens removed.
already tried the small stuff. For AM it’s time to consider just about any
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