© Ildar Sagdejev / Wikimedia Commons / CC-BY-SA-3.0 The author is technical editor of Radio World Engineering Extra.
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 all?
It’s a 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.
Further 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.
We have already tried the small stuff. For AM it’s time to consider just about any idea.
Comment on this or any story. Post below or write to [email protected]