Source: https://www.hfunderground.com/wiki/index.php?title=Part_15&diff=9524&oldid=prev
Timestamp: 2020-02-24 04:56:36
Document Index: 521456345

Matched Legal Cases: ['art 15', 'art 15', 'art 95', '§ 15', '§ 15', 'art 15']

Revision as of 16:48, 7 October 2019 (view source)
(→15.235 Operation within the band 49.82-49.90 MHz.)
Revision as of 18:26, 7 October 2019 (view source)
*49.850 MHz - Channel I (or channel A, or channel 1)
*49.850 MHz - Channel I
*49.870 MHz - Channel II (or channel B, or channel 2)
*49.870 MHz - Channel II
Revision as of 18:26, 7 October 2019
Part 15 is the section of FCC regulations dealing with unlicensed radio operation. Operation in several bands is allowed:
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
§ 15.229 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.
This section applies to cordless telephones. 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).
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.
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.
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.
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, 16.61667 MHz x3 = 49.850 MHz, etc.) and simple FM modulation. Use of the 15 kHz channels is generally ignored. Channel labeling or naming is arbitrary, including:
Other equipment use random 10 kHz / 20 kHz channel spacing, with offsets from the standard 15 kHz channel steps.
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.