Part 15

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Part 15 is the section of FCC regulations dealing with unlicensed radio operation. Operation in several bands is allowed:


Contents

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.

(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.

(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.

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

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).

49.600 MHz - 50.000 MHz band (47 CFR 15.235 subband 49.820 MHz - 49.900 MHz) shared with military users and other Part 15 devices, including first-generation analog cordless phones. Cordless phones are covered under a separate section of Part 15 - specifically 15.233 [47 CFR 15.233], but the same 10,000 microvolts/meter at 3 meters field strength limitation applies. Bandwidth limited to 20 kHz (generally FM voice, same deviation as VHF low band).

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.

The Radio Shack and Maxon 49 MHz walkie talkies generally have a communication range of around 1/8 mile [200m] in built-up 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.

This equipment provides preppers and militia types 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.

  • 49.830 MHz - Channel 1/Channel A [cordless phone headset channel 21]
  • 49.845 MHz - Channel 2/Channel B [cordless phone headset channel 17]
  • 49.860 MHz - Channel 3/Channel C [cordless phone headset channel 18]
  • 49.875 MHz - Channel 4/Channel D [cordless phone headset channel 20]
  • 49.890 MHz - Channel 5/Channel E [cordless phone headset channel 22]

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.

  • 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 (standard channel A)
  • 49.845 MHz - Channel 2 (standard channel B)
  • 49.860 MHz - Channel 3 (standard channel C)
  • 49.875 MHZ - Channel 4 (standard channel D)


Some 2 channel transmitters use arbitrary channel labeling, including:

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

Other channel plans include

  • 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

Most 2 channel devices use frequencies that are at least 20 kHz apart from each other. 3 channel equipment often use 30 kHz channel spacing.

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

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

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. Maximum bandwidth 10 kHz, de facto 15 kHz channel steps for R/C use. 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, 49.865 MHz, etc. Low-cost toys and other devices may purposely use frequencies between channels such as 49.825 MHz, 49.870 MHz, etc.

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.



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