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Ontario Technoblog

Ontario Emperor technology blog.

This blog has been superseded by the mrontemp blog
Location: Ontario, California, United States

Sometime audio artist. Email comments on this blog to the gmail account mrontemp.

Tuesday, September 06, 2005

Software Defined Radio, Software Communications Architecture

From the Communications Research Centre Canada:

Recent developments in radio technology are poised to make single-waveform, hard-coded radios obsolete. The wave of the future belongs to software reprogrammable radios, which can be reconfigured to adapt to changing communications protocols and frequency bands.

Communications Research Centre Canada (CRC) is at the forefront in the development of this revolutionary technology, known as Software Defined Radio (SDR)....

Software Defined Radio is the term...to describe a radio that provides software control of a variety of modulation techniques and waveform requirements, of current and evolving standards, over a broad frequency range. This technology uses a common hardware platform to accommodate the different communications standards and technologies, via software modules and firmware.

The concept of SDR is rapidly gaining commercial popularity, not only for cellular phone applications but also for wireless computer networking and entertainment broadcasting, such as digital radios and televisions. Emergency response organizations (e.g., police, firefighters and ambulance), the public and the military will all benefit from the vastly improved communications available through SDR....

For SDR to work to its full potential and offer truly interoperable radios, the underlying software architecture must offer a development framework that segregates the RF, digital signal processing hardware and software, and provide a mechanism to tie them all together. The architecture must also be open source to avoid incompatible proprietary solutions.

The Software Communications Architecture (SCA) is such an architecture. The SCA is a set of specifications describing the interaction between the different software and hardware components of a radio and providing software commands for their control.

It has been developed by the U.S. Department of Defense Joint Tactical Radio System (JTRS) project, adopted by the Software Defined Radio Forum (SDRF), and is being promoted to the Object Management Group (OMG) to become an international standard....

From Fineware:

SCA stands for Subsidiary Carrier Authorization, a hidden channel (or channels) on some FM broadcasts. Technically, these subchannels may reside on 57, 67 or 92 kHz away from the main carrier, however, the 67 kHz channel is used most often. Some of these broadcasts may contain what's commonly known as Muzak (elevator music), Physician's Radio Network, Radio Talking Book (or Radio for the Blind), or some other pay service. Some services consist of data streams that consist of stock and commodities quotes, which may be encrypted....

This information is provided by the author solely for the purposes of entertainment and education. Readers are forewarned that the use of this curcuit will violate the Electronic Communications Protection Act of 1986 in the United States of America. Since construction may imply its use by some law officials, the reader is further cautioned that this action may likewise be considered illegal.

Illegal? Well, let's look back at the 1989 article. Hush hush secret junk and all.

It has been ignored by the consumer press. The high fidelity and stereo
industry doesn't talk about it. Certainly, few FM listeners are aware of it.
"It" is a medium of communication available free for the taking in almost all
parts of North America -- namely, FM subcarrier broadcasting.

First demostrated in 1953 by FM's inventer, the late Edwin H. Armstrong,
multiplexing of more than one program on a single station's carrier was
authorized to begin in the United States by the Federal Communications
Commission in 1955. Long since eclipsed in the public eye by another
multiplexing development, FM stereo, subcarrier FM has been largely the
province of special interest groups, instead of the public.

FM-SCA listening has enjoyed a steady growth in the last 30 years, thanks
largely to magazine articles showing how to assemble FM subcarrier contruction
kits and to companies supplying the components and radios to make such
listening possible....

My FM ATLAS AND STATION DIRECTORY has publicized the existence and nature of
SCA programming, and this led to curiousity as to how SCA-FM can be received.
This caused us in 1977 to explore the business, legal and technical aspects of
SCA tuning-in. In the years since, we've offered SCAdapter devices to the
public, as well as conversions of radios to pick up SCA transmissions.

In our early days we fought off several threats of lawsuits from entrenched
SCA interests who would like to keep SCA private and out of the public's
radios. More recently, the FCC deregulated SCA, allowing more uses of the SCA
signal, including data services and freeing stations from having to get
specific advance approval before embracing an SCA ["Subsidiary Communications

That term was changed to SCS ["Subcarrier Communications Service"], with
this article using the letters SCS or SCA interchangeably. Canada has a similar
service called SCMO.

In deregulating the medium, the FCC utilized our data showing the degree of
SCA utilization nationally by broadcasters. In so doing, the FCC announced its
intent to encourage broadcasters to make greater use of SCA, and it created a
new SCS channel, 92 kHz, which enabled broadcasters to make greater use of
their station bandwidth.

The two common subcarrier frequencies are thus 67 kHz (the granddaddy of
them all), and 92 kHz. One FM station can send out all three programs
simultaneously -- a stereo program to its regular audience and two separate
programs on SCA, such as a radio reading service to the blind at 67 kHz and
foreground music on 92 kHz.

Another channel -- 57 kHz -- is in use exclusively for data. Data includes
highway condition alertings in many metro areas and digital paging. It is a
channel not favored by at-home listeners, because it is devoid of talk or music

Because FM-SCA is a technology which is multiplexed and "readily available"
to large numbers of the public, tuning in its transmission is no more sinister
than owning and using a police radio, public service band scanner, radar
detector, listening to FM stereo, or watching color television. Virtually all
laws prohibiting the use of such devices have been struck down by the courts as
being in violation of the First Amendment to the Constitution....

Anybody questioning the legality of tuning in SCA should contact local
broadcasters for a letter of permission authorizing tuning in their subcarriers
for noncommercial, hobby purposes. Please send us any such letters you receive
from broadcasters....

SCA's programming has considerably broadened since 1977, when most of the
use of the medium was background music to stores. Radio reading services to the
blind were just getting underway; they are now found in most metropolitan
areas, or across entire states, usually on the subcarriers of public stations.
Overlapping reading services can be tuned in in such areas as Wichita, Kansas
and along the Minnesota-Wisconsin borders....

It is a pity that most SCA radios are fixed tuned, getting only one station,
and not allowing blind citizens who travel or who live in areas having
overlapping signals to tune in all that they could. There is ethnic programming
in many major markets, at either 67 or 92 kHz. Foreground or light rock music
predominate on 92 kHz. Many stations have an easy-listening SCA at 67 kHz. With
the demise of easy-listening from many commercial FM stations, SCA remains the
only way for millions of people to hear that format on radio.

In certain areas of the country you can tune in religion, medical news,
relaying of sports and special events, or even AM stations on SCS. With many AM
stations having financial troubles, it might make sense for them to direct
their efforts to being on the SCA of a nearby FM station than face the prospect
of ultimately closing down....

SCA has a monaural signal with a bandwidth up to 7,000 Hz, or about as good as the
best AM stations send out. Its benefits include coverage range similar to the
main station stereo signal, and the ability to broadcast a whole new program
without having to create new transmitters, build new towers, or pay the power
bills necessary for running a complete radio station. SCS is truly a piggyback

Listeners should be aware, too, that many a public or religious FM station
that may be begging you for funds could be raking in the dollars by offering
for-profit data, music, paging or other services -- something they're not very
likely to mention, but nevertheless a significant source of income or potential

Being able to tune in SCA at home, ona portable, or on a car radio is the
absolute elitism in radio listening. You are in a class unlike 99 percent of
your neighbors. Considering that SCS is sent out with only 10 percent of the
energy that the main FM station uses, reception of SCS under most conditions is
surprisingly good and uncritical when the receiving equipment is properly
installed and used, although it does suffer from multipath distortion and
crosstalk problems....

More information here.


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