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| It is the policy of CellComm, 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. |
| FCC's Bulletin titled; "Understanding Low Power, Non Licensed Transmitters" 911K |
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| FCC's Part 15 Rules & Regulations, 361K |
| For additional FCC information, go to the FCC Home Page |
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| A brief introduction to the rules of the FCC and your kit built AM/FM Transmitter |
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| It is the policy of CellComm, 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 CellComm, 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 radiator". |
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| CellComm 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. CellComm 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 accepted. |
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| In the United States, this is how the FCC regards your transmitter kit: |
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| 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, youre asking for trouble! |
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| 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. |
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| 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 CellComm cannot be held responsible for any violation thereof. |
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| 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. |
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| 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. |
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| 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. |
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| 4. FCC Rules pertaining to field strength do not differ for "stereo" or "monaural" transmissions. |
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| 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. |
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| 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 observed: |
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| 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. |
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| 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. |
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| 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 interference." |
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| 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. |
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| UNDERSTANDING LEGAL "FIELD STRENGTH" |
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| 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: |
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| DISTANCE FROM TRANSMITTER ANTENNA |
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| METERS |
| FEET |
| FIELD STRENGTH (µV) |
| TOTAL AREA RECEIVED |
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| 3 |
| 10 |
| 250 |
| 314 FT |
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| 6 |
| 20 |
| 125 |
| 1256 FT |
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| 12 |
| 39 |
| 63 |
| 4800 FT |
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| 24 |
| 78 |
| 31 |
| 19113 FT |
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| 48 |
| 157 |
| 15 |
| 1.8 ACRES |
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| 96 |
| 315 |
| 7.5 |
| 7.2 ACRES |
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| 192 |
| 630 |
| 3.8 |
| 28.6 ACRES |
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| 384 |
| 1260 |
| 1.9 |
| 11.4 ACRES |
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| 768 |
| 2520 |
| .95 |
| 458 ACRES |
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| 1536 |
| 5036 |
| .5 |
| 1830 ACRES |
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| 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. |
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| 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. |
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| "Why talk about acres"? |
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| There are three reasons to translate our look at "field strength" into "acres". |
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| 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. |
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| It's can be seen that your signal can easily and legally serve a school campus or wilderness camp. |
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| 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! |
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| 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. |
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| CHOOSING AN OPERATING FREQUENCY: |
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| (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 particular frequency. |
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| (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. |
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| SUMMARY: |
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| 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 doesnt 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! |
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| 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. |
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| Lawful use suggestions: |
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| Build and adjust this kit strictly according to the published instructions. |
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| Use the whip antenna supplied with the Ramsey case set, CFM. |
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| Do not modify your kit in any way. |
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| Check your intended operating frequency very carefully, to ensure you will not cause interference to reception of licensed broadcasting. |
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| If you receive ANY complaint about your transmissions interfering with broadcast reception, stop or change your operation IMMEDIATELY. |
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| If you are contacted by the FCC regarding use of this device, cooperate fully and promptly. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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: |
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| NOTICE: |
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| The radio-frequency "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. |
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| The individual kit-builder and all users of this device assume responsibility for lawful uses |
| conforming to FCC Part 15 Rules. Operation is subject to the following two conditions: |
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| 1. This device may not cause harmful interference, and |
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| 2. This device must accept any interference received, including interference that may cause undesired operation. |
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| Final comment: |
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| 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 communications history. |
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| Learn the rules...observe them...and have fun in radio |
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