Part 15

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Revision as of 12:47, 3 April 2020

Part 15 is one of the sections of FCC regulations (47 C.F.R.) dealing with unlicensed low-power radio operation. The FCC defines these low-power transmitters as intentional radiators. See also: Part 15 beacons. Operation in several bands is allowed, including low frequency 160-190 kHz, medium frequency/medium wave (AM broadcast band), HF frequencies and various VHF/UHF bands. The bands listed below is not an exhaustive list of all bands/frequencies available under Part 15.

15.217 Operation in the band 160-190 kHz.

(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed one watt.

(b) The total length of the transmission line, antenna, and ground lead (if used) shall not exceed 15 meters.

(c) All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification may be based on measure- ments at the intentional radiator's antenna output terminal unless the in- tentional radiator uses a permanently attached antenna, in which case com- pliance shall be demonstrated by measuring the radiated emissions.

15.218 Operation in the band 510-1705 kHz.

(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed 100 milliwatts.

(b) The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters.

(c) All emissions below 510 kHz or above 1705 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification may be based on measure- ments at the intentional radiator's antenna output terminal unless the in- tentional radiator uses a permanently attached antenna, in which case com- pliance shall be demonstrated by measuring the radiated emissions.

15.221 Operation in the band 525-1705 kHz.

(a) Carrier current systems and transmitters employing a leaky co- axial cable as the radiating antenna . . . .

15.225 Operation within the band 13.553-13.567 MHz.

The 22 meter band or the 13.56 MHz 13560 kHz 13553 kHz - 13567 kHz band is very popular with hobbyists due the relatively higher power allowed compared to other Part 15 bands. See here for a list of 22-meter band beacons.

(a) The field strength of any emissions within this band shall not exceed 10,000 microvolts/meter at 30 meters.

(b) The field strength of any emissions appearing outside of this band shall not exceed the general radiated emission limits shown in 15.209.

(c) The frequency tolerance of the carrier signal shall be maintained within +/- 0.01% of the operating frequency over a temperature variation of -20 degrees to +50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. For battery operated equipment, the equip- ment tests shall be performed using a new battery.

15.227 Operation within the band 26.98-27.28 MHz.

11 meter band 27 MHz operations under Part 15. 26.980 MHz - 27.280 MHz (covers the area between CB channels 2 and 28 - 26.975 MHz to 27.285 MHz).

(a) The field strength of any emission within this band shall not exceed 10,000 microvolts/meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. The provisions in 15.35 for limiting peak emissions apply.

(b) The field strength of any emissions which appear outside of this band shall not exceed the general radiated emission limits in 15.209.

Many toy R/C transmitters operate under this section of Part 15 and not Part 95. There are others that operate under Part 95. Cheaper equipment operates under the Part 15 limits while other equipment will transmit much higher power (4 watts or 25 watts) if accepted for Part 95 Radio Control Radio Service (RCRS) operation. Toy RC transmitters, some wireless computer mice and other very short range devices generally use 27.145 MHz but may technically use any frequency between 26.980 MHz and 27.280 MHz. This band is shared with the CB radio service (26.960 MHz to 27.410 MHz) and the ISM band (26.957 MHz to 27.283 MHz).

RC frequencies:

• 26.995 MHz
• 27.045 MHz
• 27.095 MHz
• 27.145 MHz
• 27.195 MHz
• 27.255 MHz

FCC authorization for Part 15 devices does not require that they operate on one of the six channels listed above. Only the higher power RCRS rules require use of the standard channels. FCC ID authorization searches indicate toys, RC cars and other devices approved for frequencies such as 27.050 MHz, 27.052 MHz, 27.0625 MHz, 27.090 MHz, 27.100 MHz, 27.120 MHz, 27.130 MHz 27.140 MHz, 27.1413 MHz, 27.142 MHz, 27.143 MHz, 27.1442 MHz, 27.1448 MHz, 27.146 MHz, 27.14625 MHz 27.147 MHz, 27.148 MHz and 27.150 MHz. The vast majority of 27 MHz Part 15 transmitters operate on 27.145 MHz, however.

Cheaper toy-grade RC devices are often sold in two versions, a 27 MHz version and a 49 MHz version. 27 MHz almost always means 27.145 MHz, and 49 MHz almost always means 49.86 MHz. There are, of course, numerous exceptions to this. Higher grade RC devices operate under the Part 95 provision vs. Part 15.

See also: the RC Radio Service, the CB Radio Service, and high power datalink systems that use 26-27 MHz.

Older versions of Part 15 allowed for voice and data transmission under 100mw within the 26.99 MHz to 27.26 MHz band (26.990 MHz - 27.260 MHz, previously referred to as the 26.970 MHz - 27.270 MHz band). Prior to updating the rules in the late 1970s, this permitted low-power CB transmissions without a license on the CB frequencies as well as low power 27 MHz walkie talkies (unlicensed) using AM or FM voice on the 27 MHz R/C frequencies. Manufacturing of devices operating under these rules stopped on March 18th, 1977 and marketing of such devices stopped on March 18th, 1978. Use of 100mw devices within the 26.99 MHz - 27.26 MHz band or the 26.97 MHz - 27.27 MHz band became under Part 15 became illegal on March 18th, 1983.

Many older-generation walkie-talkies operate under this now defunct provision and it is possible to find these devices on the secondhand market, even though they remain technically illegal to use.

However, the updated versions continued to allow AM, FM or CW (A3, F3 or A1) emissions on the 26.995 MHz, 27.045 MHz, 27.095 MHz, 27.145 MHz, 27.195 MHz or 27.255 MHz frequencies, with 20 kHz bandwidth limits and the usual 10,000 microvolts/meter at 3 meters requirement.

15.229 Operation within the band 40.66-40.70 MHz.

This band is not used for R/C purposes in the United States. It is used for alarm systems, very short range sensor systems and other purposes. Short-range or toy R/C devices use 26 MHz / 27 MHz, 49 MHz, 72 MHz / 75 MHz or the 2.4 GHz unlicensed band in the United States.

§ 15.229 Operation within the band 40.66-40.70 MHz. (a) Unless operating pursuant to the provisions in § 15.231, the field strength of any emissions within this band shall not exceed 1,000 microvolts/meter at 3 meters. The 40.660 MHz to 40.700 MHz band is heavily used for short range devices (SRDs) and RC model control in Europe and elsewhere.

(b) As an alternative to the limit in paragraph (a) of this section, perimeter protection systems may demonstrate compliance with the following: the field strength of any emissions within this band shall not exceed 500 microvolts/meter at 3 meters, as determined using measurement instrumentations employing an average detector. The provisions in § 15.35 for limiting peak emissions apply where compliance of these devices is demonstrated under this alternative emission limit.

(c) The field strength of any emissions appearing outside of this band shall not exceed the general radiated emission limits in § 15.209.

(d) The frequency tolerance of the carrier signal shall be maintained within ±0.01% of the operating frequency over a temperature variation of −20 degrees to + 50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. For battery operated equipment, the equipment tests shall be performed using a new battery.

15.233 Operation within the bands 43.71-44.49 MHz, 46.60-46.98 MHz, 48.75-49.51 MHz and 49.66-50.0 MHz.

This section applies to cordless telephones. 43.71 MHz to 44.49 MHz (43.72 MHz to 44.48 MHz), 46.60 MHz to 46.98 MHz (46.61 MHz to 46.97 MHz), 48.75 MHz to 49.51 MHz (48.76 MHz to 49.50 MHz and 49.66 MHz to 50.0 MHz (49.67 MHz to 49.9 MHz). Note that the frequencies overlap with the VHF low band business radio band, the military bands, the 49 MHz RC 49 MHz remote control device frequencies and 49 MHz short range devices (walkie-talkies, baby monitors, etc.) The original 10 channel cordless phones used the 46.600 MHz - 47.000 MHz and 49.650 MHz to 50.000 MHz ranges only (46.610 MHz - 46.970 MHz and 46.670 MHz - 49.990 MHz).

While still legal to own and operate, cordless phones that use this band have all but disappeared.

15.233 Operation within the bands 43.71-44.49 MHz, 46.60-46.98 MHz, 48.75-49.51 MHz and 49.66-50.0 MHz. (a) The provisions shown in this section are restricted to cordless telephones.

(b) An intentional radiator used as part of a cordless telephone system shall operate centered on one or more of the following frequency pairs, subject to the following conditions:

(1) Frequencies shall be paired as shown below, except that channel pairing for channels one through fifteen may be accomplished by pairing any of the fifteen base transmitter frequencies with any of the fifteen handset transmitter frequencies.

(2) Cordless telephones operating on channels one through fifteen must:

(i) Incorporate an automatic channel selection mechanism that will prevent establishment of a link on any occupied frequency; and

(ii) The box or an instruction manual which is included within the box which the individual cordless telephone is to be marketed shall contain information indicating that some cordless telephones operate at frequencies that may cause interference to nearby TVs and VCRs; to minimize or prevent such interference, the base of the cordless telephone should not be placed near or on top of a TV or VCR; and, if interference is experienced, moving the cordless telephone farther away from the TV or VCR will often reduce or eliminate the interference. A statement describing the means and procedures used to achieve automatic channel selection shall be provided in any application for equipment authorization of a cordless telephone operating on channels one through fifteen.

• Base Frequency 43.720 MHz - Handset Frequency 48.760 MHz - Channel 1
• Base Frequency 43.740 MHz - Handset Frequency 48.840 MHz - Channel 2
• Base Frequency 43.820 MHz - Handset Frequency 48.860 MHz - Channel 3
• Base Frequency 43.840 MHz - Handset Frequency 48.920 MHz - Channel 4
• Base Frequency 43.920 MHz - Handset Frequency 49.020 MHz - Channel 5
• Base Frequency 43.960 MHz - Handset Frequency 49.080 MHz - Channel 6
• Base Frequency 44.120 MHz - Handset Frequency 49.100 MHz - Channel 7
• Base Frequency 44.160 MHz - Handset Frequency 49.160 MHz - Channel 8
• Base Frequency 44.180 MHz - Handset Frequency 49.200 MHz - Channel 9
• Base Frequency 44.200 MHz - Handset Frequency 49.240 MHz - Channel 10
• Base Frequency 44.320 MHz - Handset Frequency 49.280 MHz - Channel 11
• Base Frequency 44.460 MHz - Handset Frequency 49.360 MHz - Channel 12
• Base Frequency 44.400 MHz - Handset Frequency 49.400 MHz - Channel 13
• Base Frequency 44.460 MHz - Handset Frequency 49.460 MHz - Channel 14
• Base Frequency 44.480 MHz - Handset Frequency 49.500 MHz - Channel 15
• Base Frequency 46.610 MHz - Handset Frequency 49.670 MHz - Channel 16
• Base Frequency 46.630 MHz - Handset Frequency 49.845 MHz - Channel 17
• Base Frequency 46.670 MHz - Handset Frequency 49.860 MHz - Channel 18
• Base Frequency 46.710 MHz - Handset Frequency 49.770 MHz - Channel 19
• Base Frequency 46.730 MHz - Handset Frequency 49.875 MHz - Channel 20
• Base Frequency 46.770 MHz - Handset Frequency 49.830 MHz - Channel 21
• Base Frequency 46.830 MHz - Handset Frequency 49.890 MHz - Channel 22
• Base Frequency 46.870 MHz - Handset Frequency 49.930 MHz - Channel 23
• Base Frequency 46.930 MHz - Handset Frequency 49.990 MHz - Channel 24
• Base Frequency 46.970 MHz - Handset Frequency 49.970 MHz - Channel 25

15.235 Operation within the band 49.82-49.90 MHz.

49 MHz devices, frequencies used and discussion.

RC transmitters generally use 49.830 MHz or 49.860 MHz as 49 MHz "RC channel 1". Children's RC toys are often offered in two versions, a "49 MHz" version and a "27 MHz" version, without any channel numbers indicated. The 27 MHz version generally will operate on 27.145 MHz. These devices are usually operating under Part 15, not Part 95 (with some rare exceptions for the 26 / 27 MHz gear. Part 15 power limit is 10,000 microvolts per meter at 3 meters (10,000 microvolts/meter at 3m).

49.6 MHz - 50 MHz (49.600 MHz - 49.975 MHz) band (47 CFR 15.235 subband 49.820 MHz - 49.900 MHz) shared with military users and cordless phones (see section above).

The Maxon PC-10 and PC-50 Personal Communicator, Maxon 49-SX, 49-H, 49-FX, 49-B5, 49-HX, 49-EA, Standard Talkman C900, and similar 49MHz radios as well as the RadioShack TRC-503, TRC-506 and TRC-512, Radio Shack (Realistic) Audionic 21-408 VOX radios and similar higher-end radios operates on the same five frequencies listed below. Some radios are single-channel only (generally 49.860 MHz, see RadioShack TRC-509, TRC-502, etc.) while others allow the user to select one of the five channels.

Even current-generation new production baby monitors are available that use the 49 MHz frequencies. Many models offer 2 channels to avoid interference with other nearby monitors. These devices remain in use despite the availability of 900 MHz/2.4 GHz, WiFi based, DECT 1.9 GHz or 5.8 MHz band audio monitors or audio/video combination devices. Analog baby monitors offer low RF radiation exposure due to their use of the VHF 49 MHz frequencies and excellent audio quality from true FM modulation within their service range. 49MHz monitor transmitters generally provide 300-600 feet range (high quality signal) depending on obstructions, antenna location/height and frequency congestion.

The Radio Shack and Maxon 49 MHz walkie talkies generally have a communication range of 600 feet to 900 feet (200-300 meters or 1/8 mile to 1/6 mile) in suburban or open areas. Simple testing with transmitters located indoors at ground level in a heavily built-up urbanized area produced reliable talk range of 300-400 feet [90-120m]. Considerably better radio talk range of and up to 1/4 mile [400m] or even further is possible with outdoor antennas, no obstructions and favorable noise levels.

Experiments with outdoor antennas and upgraded 49 MHz walkie talkie antennas show a range increase of 1.5x to 2x compared to regular rubber duck antennas. Maximum range of consistent coverage increased to approx. 1800-2000 feet from transmitter site. Signal heard (poor copy) past 1/2 mile from transmitter site. Reliable communication range of 3/8 of a mile or so (several city blocks) was achieved. Without the external antenna, range can be expected to be closer to 1/4 of a mile or so handheld radio to handheld radio. This is ideal for the purposes listed below. Militia intra-squad radio (not inter squad radio), communications with somebody 2-3 houses down, etc. when you don't want somebody 1-2 miles away to be able to listen in.

This equipment provides preppers and militia users with a unique short-range low probability of intercept (LPI) radio communications capability that higher-power VHF/UHF services like FRS, GMRS, MURS doesn't provide. The Radio Shack / Realistic TRC-503, TRC-512 and similar 49 MHz walkie talkies specs appear to indicate 16K0F3E emission for voice / 16K0F3D for tone emission. The Maxon PC-50 five channel transceiver apparently uses 4.5 kHz FM deviation, for 18 kHz bandwidth - 18K0F3E emission.

• 49.830 MHz - Channel 1/Channel A
• 49.845 MHz - Channel 2/Channel B
• 49.860 MHz - Channel 3/Channel C
• 49.875 MHz - Channel 4/Channel D
• 49.890 MHz - Channel 5/Channel E

Other Part 15C equipment using 49.82 MHz - 49.9 MHz or a portion of (for example, 49.86 MHz - 49.89 MHz) use different channel plans - 20 kHz channels instead of 15 kHz steps. FM voice room monitors for continuous transmit around 0.0012 mw. Emissions include 20K0F3E regular FM (5 kHz deviation). Other devices use narrower bandwidth, with 3 kHz deviation - 12K0F3E emission, 3.25 kHz deviation - 13K0F3E emission, 3.5 kHz deviation - 14K0F3E emission, 3.75 kHz deviation - 15K0F3E emission, 4 kHz deviation - 16K0F3E emission reported. Older baby monitors and other devices report wider FM - up to 30 kHz bandwidth 30K0F3E for some applications. At least one baby monitor on the market uses AM mode with 15 kHz bandwidth on two non-standard frequencies - see below.

• 49.830 MHz - Channel 1
• 49.850 MHz - Channel 2
• 49.870 MHz - Channel 3
• 49.890 MHz - Channel 4

FCC certification records for room monitors (continuous transmit) sold in 2019 indicate use of FM voice mode for modulation and “CW” transmit with four selectable channels:

• 49.830 MHz - Channel 1
• 49.845 MHz - Channel 2
• 49.860 MHz - Channel 3
• 49.875 MHZ - Channel 4

Modern equipment generally uses 2 switchable channels. Some of these transmitters use a simple 16.6xxx MHz crystal with a frequency tripler circuit (16.610 MHz x3 = 49.830 MHz - 16.61415 MHz x3 = 49.8425 MHz, 16.615 MHz x3 = 49.845 MHz, 16.616 MHz x3 = 49.848 MHz, 16.61667 MHz x3 = 49.850 MHz, 16.620 MHz x3 = 49.860 MHz etc.) and simple FM modulation. Frequency steps, channel plans and channel spacing is random and channel labeling or naming is arbitrary, including:

• 49.845 MHz - Channel X
• 49.875 MHz - Channel Y

Or,

• 49.830 MHz - Channel A
• 49.860 MHz - Channel B

Or,

• 49.845 MHz - Channel A
• 49.890 MHz - Channel B

Or,

• 49.840 MHz - Channel A
• 49.870 MHz - Channel B

Or,

• 49.850 MHz - Channel I
• 49.870 MHz - Channel II

Or,

• 49.825 MHz - Channel 1
• 49.845 MHz - Channel 2

Or,

• 49.870 MHz - Channel 1
• 49.890 MHz - Channel 2

Or,

• 49.840 MHz - Channel 1
• 49.860 MHz - Channel 2

Or,

• 49.842 MHz - Channel 1 (49.8425 MHz or 49.843 MHz offset)
• 49.860 MHz - Channel 2 (49.8625 MHz or 49.863 MHz offset)

Or,

• 49.840 MHz - Channel A
• 49.885 MHz - Channel B

Or,

• 49.830 MHz - Channel A
• 49.875 MHz - Channel B

Or,

• 49.840 MHz - Channel A
• 49.876 MHz - Channel B (specifically designed to operate off-center channel - 49.876 MHz per FCC ID documentation)

Or,

• 49.840 MHz - Channel A
• 49.890 MHz - Channel B

Or, for devices with two channel sets (A/B channels or X/Y channels) with 30 kHz channel spacing:

• 49.830 MHz - Channel A
• 49.860 MHz - Channel B
• 49.850 MHz - Channel X
• 49.880 MHz - Channel Y

FCC authorization for equipment using AM mode instead of FM has been found for baby monitor use. The channels / frequencies listed in the authorization are:

• 49.870 MHz - Channel A (actually closer to 49.885, 49.8875 or 49.890 MHz)
• 49.810 MHz - Channel B (actually closer to 49.825 or 49.830 MHz)

It is unknown how this equipment (FCC ID L2555005) was approved for use under Part 15. The authorization specifically mentions use of amplitude modulation (AM) for voice transmission on the nominal frequencies of 49.81 MHz and 49.87 MHz. Test reports show the transmitter actually transmits closer to 49.825 MHz for Channel B and 49.880 MHz for Channel A. The Part 15 FCC approval test report indicates the center frequencies were actually 49.8225 MHz or 49.825 MHz and 49.880 MHz or 49.8825 MHz. Testing documentation shows a 16.8 kHz bandwidth for Channel A [center frequency 49.888 MHz) and a 15.6 kHz bandwidth for Channel B [center frequency 49.828 MHz].

15 kHz wide band AM modulation appears to be used. According to the schematic provided with the authorization paperwork, the device in question uses two crystals for frequency generation - 16.610 MHz x3 (for 49.830 MHz) for Channel B and 16.630 MHz x3 (for 49.890 MHz) for Channel A. Testing indicates rather loose frequency tolerance (49.828 MHz instead of 49.830 MHz and 49.888 MHz instead of 49.890 MHz).

Other equipment use random 10 kHz / 20 kHz channel spacing, with offsets from the "standard" 15 kHz channel steps.

• 49.830 MHz - Channel 1
• 49.850 MHz - Channel 2
• 49.860 MHz - Channel 3
• 49.870 MHz - Channel 4
• 49.880 MHz - Channel 5
• 49.890 MHz - Channel 6

Other room monitor equipment with the following available channels is/was on the market:

• 49.835 MHz - Channel A
• 49.850 MHz - Channel B
• 49.865 MHz - Channel C

Or,

• 49.830 MHz - Channel A
• 49.860 MHz - Channel B
• 49.890 MHz - Channel C

In addition to monitors, baby monitors, wireless microphones and similar devices, there were/are wireless doorbells and intercom systems sold that use the 49 MHz Part 15 band. One such device uses the following frequencies:

• 49.835 MHz - Channel 1/A
• 49.860 MHz - Channel 2/B
• 49.885 MHz - Channel 3/C

Even with the 900 MHz, 2.4 GHz, 5.8 GHz and 1.9 GHz DECT bands available, the 49 MHz band is still heavily used by room monitors, wireless headphones, wireless intercom/doorbell systems, etc.

Covered under FCC Part 15 47 CFR 15.235 Operation within the band 49.82-49.90 MHz.

Sometimes frequencies may be off by several kHz. For example, 49.845 MHz may be closer to 49.840 MHz, 49.847 MHz or even 49.850 MHz, 49.860 MHz may be closer to 49.855 MHz, 49.8625 MHz, 49.865 MHz, etc. Apparently some manufacturers did/do this intentionally, likely to reduce interference issues. Certain name-brand baby monitors, for example, purposely operate off-frequency. For example, FCC authorization documents indicate a baby monitor system designed to operate on 49.862 MHz (49.8625 MHz). Another baby monitor features two channels, 49.840 MHz and 49.876 MHz. Third party testing and circuit designs specify 49.876 MHz instead of 49.875 MHz or 49.880 MHz. 49.8875 MHz instead of 49.885 MHz or 49.890 MHz. The specifications also call for a 25 kHz wide channel (20K0F3E FM voice). Another single channel design uses 49.87125 MHz (appears to be closer to 49.872 MHz than 49.871 MHz) instead of 49.870 MHz or 49.875 MHz.

49 MHz R/C transmitters usually use 49.830 MHz, 49.860 MHz or 49.890 MHz. As noted earlier, frequencies may vary +/- several kHz. Baby monitors are usually found on 49.83 MHz, 49.86 MHz or 49.89 MHz. It's common for a set of R/C toys to be sold with one toy using a 49 MHz RC frequency and the other using a 26 MHz or 27 MHz RC frequency.

The 49.82 MHz to 49.90 MHz band allows for personal hobby transmitters up to 100mw output with any modulation as long as the modulation stays within the 49.82-49.9 MHz band. This provision within Part 15 opens up opportunities for 49 MHz beacons, provided an effective antenna is used.