Part 15

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(15.235 Operation within the band 49.82-49.90 MHz.)
(15.235 Operation within the band 49.82-49.90 MHz.)
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*49.870 MHz - Channel 1
*49.870 MHz - Channel 1
*49.890 MHz - Channel 2
*49.890 MHz - Channel 2
 +
 +
Or,
 +
 +
*49.840 MHz - Channel 1 (49.843 MHz or 49.8425 MHz offset)
 +
*49.860 MHz - Channel 2 (49.863 MHz or 49.8625 MHz offset)
Or,  
Or,  

Revision as of 15:13, 5 October 2019

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.

Many toy R/C transmitters operate under this section of Part 15 and not Part 95. Toy RC transmitters 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).

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).

49.6 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 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. 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.


  • 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 (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.

  • 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

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

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

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. 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.