A brief introduction to the rules of the FCC and your
kit built AM/FM Transmitter
It is the policy of Ramsey
Electronics, Inc., that knowing and observing the lawful
use of all kits is a first responsibility of our kit
user/builders. We do not endorse any unlawful use of any
of our kits, and we try to give you as much common sense
help about normal and lawful use as we can. Further, it
is the policy of Ramsey Electronics, Inc., to cooperate
with all applicable federal regulations in the design
and marketing of our electronics kit products. Finally,
we urge all of our overseas customers to observe the
regulations of their own national telecommunications
authorities. In all instances, compliance with FCC rules
in the operation of what the FCC terms an
"intentional radiator" is always the
responsibility of the user of such an "intentional
Ramsey Electronics® only offers
this information to make the user aware of the full
impact a transmitter can have. In no way should this
brief discussion be construed as a definition of the FCC
rules, it is the users obligation to obtain a copy of
the rules and operate legally according to them. Ramsey
Electronics® makes no representation as to the
following discussion being legally correct - it is
simply offered as an introduction to the
responsibilities that a user must realize. To
order your copy of the FCC rules part 15, call the US
Government, Superintendent of Documents, at
202-512-1800, or fax at 202-512-2250. To order the
correct document, ask for "CFR Title 17: Parts 1 to
199." The cost is $24.00. Master Card and Visa are
In the United States, this is how the
FCC regards your transmitter kit:
Licensed FM broadcast stations and their listeners
have ALL the rights! Your use of a device such as the FM-25A kit MAY
have some limited privileges in locally-unused band space, but your
non-licensed use of the FM-25A has absolutely NO rights at all over the
rights of licensed broadcast operators and the rights of their listeners
to interference-free reception. If your operation of a device such as
the FM-25A interferes with ANYBODY'S use or enjoyment of an FCC licensed
transmission of any kind, your only choice is to IMMEDIATELY terminate
or change the operation of your low-power transmitting device so as to
cause no more interference. That's it! No discussion, no exceptions - if
you persist in causing interference to other folks, you’re asking for
Unlicensed operation of small transmitting devices is
discussed in "Part 15" of the FCC Rules. These Rules are
published in 100 "Parts," covering everything imaginable
concerning the topic of "Telecommunications." It is a
fascinating read and well worth the modest cost. The six books
containing the FCC Rules are section 47 of the complete Code of Federal
Regulations, which you are likely to find in the Reference section of
your Public Library. If you have questions about the legal operation of
your FM-25A or any other kit or home-built device which emits RF energy,
it is your responsibility to study the FCC regulations. It is best if
YOU read (and consult with a lawyer if you are in doubt) the rules and do
not bother the understaffed and busy FCC employees with questions that
are clearly answered in the rules.
Here are the primary "dos and don'ts"
picked from the current FCC Rules, as of May, 1990. This is only a brief
look at the rules and should not be construed to be a complete legal
interpretation! It is up to you to operate within the proper FCC rules
and Ramsey Electronics® cannot be held responsible for any
1. In the past, no "two-way communications"
use of the 88-108 MHz FM broadcast band was permitted. This prohibition
does not appear in the current edition of Part 15. Previous editions of
Part 15 discussed "wireless microphones" (such as Ramsey FM-1,
FM-4, etc.), while the June 23, 1989, revision eliminates this
discussion in favor of more detail regarding computer and TV peripherals
and other modern electronic conveniences. However, it is not immediately
clear that the 1989 revision of the FCC Rules Part 15 necessarily
"cancels" previous regulations. Laws and rules tend to remain
in force unless they are specifically repealed. Also, FCC Rule 15.37
discusses "Transitional Provisions for Compliance with the
Rules," and states in item (c): "There are no restrictions on
the operation or marketing of equipment complying with the regulations
in effect prior to June 23, 1989." It is up to you to read the
rules yourself and understand them.
2. It is the sole responsibility of the builder-user
of any FM broadcast-band device to research and fully avoid any and all
interference to licensed FM broadcast transmission and reception. This
discussion will later give you practical advice on how to do a good job
of finding a clear frequency, if one is available.
3. For some frequency bands, the FCC sets 100
milliwatts (0.1 watt) as the maximum permitted power output for
unlicensed, home-built transmitting devices, and that the combined
length of your antenna and feedline (coaxial cable or other) must not
exceed 10 feet. The technical standards for 88-108 MHz are very
different, primarily concerned with band width and RF field strength.
4. FCC Rules pertaining to field strength do not
differ for "stereo" or "monaural" transmissions.
5. Broadcasting on the grounds of a school using the
AM broadcast band is specifically permitted and encouraged between 525
and 1705 KHz under Part 15.221. Our AM-1 or AM-25 AM radio broadcast kit
could be used for this application.
6. FCC Rule No. 15.239 specifically addresses
operation in the 88-108 MHz FM broadcast band for which your FM-25A
transmitter kit is designed. However, this Rule does not, by itself,
tell you everything you need to know about using a device of this kind.
Therefore, we are noting a series of Part 15 regulations which should be
||The "bandwidth" of your transmission is
limited to 200 KHz, centered on the actual operating frequency. This
is a "generous" limitation designed to accommodate cruder
FM devices. Properly built and adjusted, the FM-25A kit operates
well within this limit. In fact, its signal should sound no
"wider" than any other FM station when listening on an
ordinary FM radio.
||FCC Rule 15.215(a) says: "Unless otherwise
stated, there are no restrictions as to the types of operations
permitted under these sections." This general provision appears
to leave you free to use your FM stereo transmitter in a manner
similar to operations of an FM broadcasting station, or to use it
for any other non-interfering, practical application.
||FCC Rule 15.5: General conditions of operation:
"(b) Operation...is subject to the conditions that no harmful
interference is caused and that interference must be accepted that
may be caused by the operation of an authorized radio station, by
another intentional or unintentional radiator, by industrial,
scientific and medical equipment, or by an incidental radiator. (c)
The operator of a radio frequency device shall be required to cease
operating the device upon notification by a Commission
representative that the device is causing harmful
||The most specific FCC regulation of 88-108 MHz FM
Broadcast band unlicensed operation is that the "field
strength" of the signal must not exceed 250 microvolts/meter at
a distance of 3 meters from the transmitter (FCC rule 15.239). If
you have any concern about this emission limit, have your device
checked by a technician with accurate measuring equipment. Remember
that the "field strength" of a signal is determined as
much by the antenna as by the RF output of the transmitter itself.
The new FCC Part 15 Rules specify a maximum
"Field Strength" of your transmitted signal. Since it is
unlikely that you have the equipment to carry out accurate field
strength measurements in microvolts, it is useful to understand at least
the theory of field strength so that you can understand both what you
can expect from such transmitters, and what limits the FCC intends.
Previous limits on nonlicensed FM-broadcast band devices were defined as
a maximum field strength of 40µV per meter measured at a distance of 15
meters. The June 1989 revised rule specifies a maximum of 250 µV per
meter, but measured at 3 meters from your antenna. The term, "250µV
per meter" means that an accurate field-strength meter with a
calibrated and scaled 1-meter antenna may indicate a maximum signal
field strength of 250µV (In contrast, non-licensed operation from 26.96
to 27.28 MHz, your standard CB walkie-talkie, is limited to a field
strength of 10,000 µV per meter at 3 meters). In all cases, the field
strength of a signal decreases in direct proportion to the distance away
from the antenna. Power decreases by the square of distance: for every
doubling in distance, the signal power is quartered, but the field
strength voltage is only halved. Using this theory, we can construct a
simple chart to show the maximum permitted performance of a non-licensed
FM band transmitter. The theoretical figures assume a simple 1 meter
receiving antenna in all cases and do not take into consideration that
reception can be greatly enhanced with larger, multi-element antennas
and preamplifiers on the receiver. In the following chart, the field
strength (theoretical minimum) gets stronger as you move from the edge
of these circular boundaries toward the antenna:
DISTANCE FROM TRANSMITTER
FIELD STRENGTH (µV)
TOTAL AREA RECEIVED
This "exercise in meters and microvolts"
demonstrates that the FCC clearly intends to limit the theoretical range
of non-licensed devices operating in this band. It also shows the
potential for causing interference at a home down the street from you.
But it also shows that you can legally put out quite a good signal over
wider areas than you might have imagined.
For other kinds of radio services, the FCC restricts
such factors as transmitter power or antenna height, which cannot really
limit the possible "range" of a transmission under good
conditions. By restricting the maximum field strength at a specific
distance from your antenna, the FCC clearly plans for your signal to
"die out" at a specific distance from your antenna, no matter
what kind of transmitter power or antenna you are using. On the other
hand, the FCC standards do make it legal and possible for you to
broadcast on a school campus, campground or local neighborhood, as long
as you remain within the field strength limitations and do not cause
interference to broadcast reception.
"Why talk about
There are three reasons to translate our look at
"field strength" into "acres".
||The first one is easy: the numbers would get too
cumbersome if we discussed your possible signal coverage in terms
of square feet or square meters.
||It's can be seen that your signal can easily and
legally serve a school campus or wilderness camp.
||And, if we remember that typical urban
single-family home sites run from 1/4 to 1/2 acre on the average, it
should become extremely clear that your obligation to avoid
interfering with broadcast reception can easily involve hundreds of
homes, before adding apartments!
In fact, the most significant distance in the above
chart is the 1.9 µV signal strength permissible at 1260 feet (about 1/4
mile), covering a circular area of about 114 acres. A quick glance at
stereo FM receiver specifications shows typical sensitivity of 1.7 µV
before considering high-gain antennas or preamplifiers. Your
non-licensed signal can provide serious competition to a public
broadcast station fifty miles away, a station which someone in your
neighborhood may have set up a special antenna to enjoy, this is why you
must carefully check to see if the frequency is occupied. Calibrated
"field strength meters" such as described in the ARRL Radio
Amateur's Handbook can detect signals down to about 100 microvolts. To
measure RF field strength below such a level, professional or laboratory
equipment and sensitive receivers are required. A "sensitive"
receiver responds to a signal of 1 or even .5 microvolts
"delivered" to the receiver input by antenna. If the antenna
is not good, the receiver cannot respond to the presence of fractions of
a microvolt of RF energy.
CHOOSING AN OPERATING
(A) It really is NOT sufficient to just
"check" the FM band for an empty frequency, using the FM
portable radio closest at hand. It is your responsibility to carefully
research what FM stations can be listened to with a good system within
the transmitting range of your FM-25A. This is especially important in
the low end of the FM broadcast band (88-92 MHz), where there are
numerous medium and low power College and National Public Radio
stations. You may not be aware of these stations but your neighbors may
be receiving them, using a good receiver and outdoor antenna.
Interfering with such reception is a direct violation of federal law. You
have no right whatsoever interfering with anyone's radio reception! The
most reliable way of finding a truly open frequency on the FM band is to
check the band with a very good FM receiving system using an external
antenna. If you do not have access to such a radio, most modern car
radios (with exterior antenna) are very sensitive and usable to help you
know what stations your neighbors really can be receiving on a
(B) In choosing an operating frequency, remember that
most "digital-tuning" receivers, whether portable, mobile or
hi-fi, are designed to tune in 200 KHz increments and therefore might
not receive well a signal operating between these pre-tuned standard
broadcasting frequencies. In order to comply with Part 15 of FCC
regulations, it is your responsibility to determine carefully that your
operation will not cause interference to broadcast reception.
The present edition of Part 15 of the FCC rules
provides detailed guidance on ALL aspects of using a low-power
transmitter such as the FM-25A. The main points to consider are; to
remain within the field strength limitations, that you may not cause any
interference whatsoever to licensed broadcast services, and that you
must be willing to put up with any interference that you may experience.
Remember, the FCC doesn’t need to be bothered by policing a privilege
given to unlicensed operators. If the rules are flagrantly violated,
they might just revoke the privilege altogether!
If you become further fascinated with the service
rendered by low-power broadcasting, other FCC regulations explain how to
apply for a license or other authorization which may permit you to
upgrade your equipment to accomplish any objective which the FCC sees to
be in the public interest and not interfering with other authorized uses
of the radio spectrum.
||Build and adjust this kit strictly according to
the published instructions.
||Use the whip antenna supplied with the Ramsey
case set, CFM.
||Do not modify your kit in any way.
||Check your intended operating frequency very
carefully, to ensure you will not cause interference to reception of
||If you receive ANY complaint about your
transmissions interfering with broadcast reception, stop or change
your operation IMMEDIATELY.
||If you are contacted by the FCC regarding use of
this device, cooperate fully and promptly.
||Do your own homework and research to understand
and comply with present and future FCC rulings concerning devices of
this kind. Do not rely only upon this short discussion.
||Do not use made-up "station call signs"
to identify your transmissions. Only the FCC has the authority to
issue such call signs. Use some other way to identify your
transmitting activity, such as "This is Stereo 90.5, Seabreeze
School Student Music Radio," and so forth.
||Identify the location and purpose of your
transmissions from time to time. This is common courtesy toward
other persons who may hear your signal. The FCC is toughest about
clandestine transmission which cost time and money to track down.
||Do not assume that the mere fact that you
purchased this kit gives you any specific right to use it for any
purpose beyond generating a low-level RF signal which is barely
detectable beyond the perimeter of your personal dwelling space.
Finally, the FCC Rules call for the posting of
printed notices on devices intended for non-licensed operation under
Part 15 Rules. You will find such notices written up for the front or
back of the instruction manual for nearly any computer or video
accessory that you have seen in recent months. Consult the Part 15 Rules
for the exact wording of such notices. Following is a text for such a
notice which responds to FCC rule making intentions:
"Intentional Radiator" device which may be
constructed from kit
parts supplied by us is intended to conform to applicable
provisions of Part 15 of FCC Rules.
The individual kit-builder
and all users of this device assume responsibility for lawful
conforming to FCC Part 15 Rules. Operation is subject to the
following two conditions:
1. This device may
not cause harmful interference, and
2. This device must
accept any interference received, including interference
that may cause undesired operation.
A well-informed person will see today's FCC Rules to
be evolving and progressively less restrictive. Even though today's
technology is far more complex than what was possible at the time of the
Communications Act of 1934, the FCC rules are becoming more relaxed,
giving radio experimenters more and more opportunities to explore many
frequency bands, using many communications modes, with no need for a
formal license of any kind. A thorough study of Part 15 of the FCC
Rules, which is completely beyond the purpose of this brief discussion,
will show you many legal uses of radio transmitting devices which do not
require licensing, either amateur or commercial. To provide more
personal and club radio learning opportunities, and to cut down on
administrative costs, today's FCC permits far more non-licensed activity
than at any time in previous history. On the other hand, today's FCC
enforcement actions get bigger fines and real prison terms for
scofflaws! From CB radio to easy entry-level Amateur Radio with
long-term licensing, to numerous unlicensed Part 15 operations, the FCC
is beginning to look out for the interest and good plans and intentions
of private citizens and school-community groups as never before in radio
Learn the rules...observe them...and have fun