Did you notice that there are 43 bands specified for LTE cellular? Did you ever wonder how specific services become assigned to their bands?
In the U.S., frequency assignments are handled by the FCC (non-government uses) and NTIA (government uses). Both agencies are required to adhere to allocations made by the International Telecommunications Union (ITU), headquartered in Geneva, Switzerland.
International coordination is necessary since radio waves don’t observe any geographic or political boundaries. If one country decided to allow broadcasting on a frequency band that was used in a nearby country for public safety agencies like police and fire departments, chaos would result. In some parts of the spectrum, such as the HF bands in which signals propagate globally, a “nearby country” could be anywhere on the planet.
One thing the framers of regional frequency allocations did not anticipate was the evolution of global mobility. VHF and UHF signals generally don’t propagate very far, so having different bands for TV, public-safety, and later, cellular telephony, in different parts of the world wasn’t a problem, since interference wasn’t an issue. It was only when people wanted their cellphones to work worldwide that this became a major problem.
The ITU convenes a World Radiocommunication Conference periodically to evaluate proposals for allocations for new services and amendments to existing allocations. The latest WRC is wrapping up as I type this. If you’re curious about exactly what sorts of changes were considered this year, the complete agenda is here.
There are items dealing with various allocations from 20 kHz all the way to “Consideration of the use of the frequencies between 275 and 3 000 GHz.”
In addition to the delegates from member states, various non-government interested parties are invited to attend as “observers”, such as the International Amateur Radio Union (IARU), International Air Transport Association (IATA) and other organizations with expertise or concerns related to spectrum allocations.
Amateur radio got a new band, at 472-479 kHz, or a bit below the existing medium-wave AM broadcast band. If you listen to your AM car radio during the day, you’ll only hear stations in your local area, up to maybe a hundred miles or so distant. At night, when medium-wave signal absorption in the D layer of the ionosphere is low, you may hear signals from stations far outside your own area.
Propagation on this new band is likely to be best at night as well. The WRC agreement only allows a maximum radiated power of 1 watt, in an effort to minimize interference to other services such as radiolocation in adjacent bands. Compare that to the AM radio stations running tens of kilowatts and antenna arrays with some gain. A signal from a “600-meter” ham station will be 40-50 dB weaker to start. And there’s the issue of antennas…a half-wave dipole for this band is about almost 1000 feet long. Few hams have that kind of space (or supports to hold it up 1000-2000 feet).
Some hams have expressed disappointment at this new allocation, since it is in a “useless” part of the spectrum and only 7 kHz wide. On the other hand, this slice of spectrum should result in some innovative techniques for detecting weak signals, design of physically-short antennas, better understanding of medium-wave propagation mechanisms, and atmospheric noise mitigation. Remember, once upon a time the governments of the world gave the hams the supposedly-useless bands below 200 meter wavelengths (above 1500 kHz), and the hams discovered long-distance short-wave propagation. And when we were also given “everything above 30 GHz,” experimenting hams found ways to use some of those bands, and we were moved up to “everything above 300 GHz.” Hams always seem to turn spectral “lemons” into lemonade.
Doug Grant received his first ham radio license from the FCC in 1967 and
his BSEE in 1975. He has logged over 30 years in the semiconductor
industry, mostly at Analog Devices, where he worked in engineering,
marketing, and product line management for a wide range of analog,
mixed-signal, RF and wireless products. He has also logged over 500,000
two-way contacts with other radio hams in every country in the world.
Doug is currently an independent consultant specializing in
semiconductor and wireless technologies.
A very interesting and informative article. This gamut of frequency bands, their range,their allocation and use and possible cross talk effects , also the environmental effects on the signal transmission are all nicely covered in this short and sweet tutorial
The new amateur radio band is interesting both due to the challenges and the fact that the Hams are still being given consideration. I would expect that the Hams would welcome another band to work and it could provide a new band for collages and universities to use for experiments in low power and compact antenna design. I wonder what they will come up with? My son is a license ham operator and I wonder if he knows.
The supposed "NEED" for more spectrum for data communication is based on what suppliers of services want to sell, not what people want to buy. Of course, if they provide it people will use it, that is the herd mentality, and marketing has mastered using it. It IS all about money.
As for the newest ham band, 472 to 479, that will be an interesting band to experiment on, with a whole lot of materials available, since the frequencies don't demand premium materials. Lots of possibilities exist, including the use of 4000 series CMOS for signal processing.
As much of a pain as it is trying to figure out the various international regulations and bandwidth allocations I am stunned that we are ever able to reach standards agreements at all. Of course it is in the best interests of business globally to have standards and bandwidth agreements it's just that when you look at how closely allocation is tied to government bureaucracy it's amazing anything ever gets decided at all!
Jon - http://www.evosite.co.uk/