WHAT’S OUR STORY?
ZFRB Free Radio Brentwood is the Delta's only all-volunteer, listener supported, community radio station. We work very hard to bring you the absolute best in Local Music, as well as talk, news, live, and volunteer created content.
HOW DO WE DO IT?
We use a network of FCC certified transmitters located in various places around Brentwood, CA.
AM Transmitter Cluster 1: This is a trio of Hamilton Rangemaster AM1000's linked together. FCC ID: NWXAM1000 These are located on the roof of the ZFRB studio.
AM Transmitter 2: Chez Radio Procaster AM Transmitter FCC ID: VCJ-AMTX20 . This is located on the Brentwood Police Department antenna tower.
AM Transmitter 3: Carrier current transmitter and coupler pushing just under 250mV @ 3 meters. FCC ID: TBD This covers downtown. Location is TBD
FM Transmitter 1-4: Broadcast Vision FM3001W FCC ID: M3R-FM3001 . Location is VARIOUS. These only cover about half a block or less.
HOW IS THIS LEGAL?
The FCC, the governing body that presides over broadcast radio, allows for unlicensed broadcast under certain rules.
For AM (the most lenient) we operate in Title 47, Part 15.219:
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 measurements at the intentional radiator's antenna output terminal unless the intentional radiator uses a permanently attached antenna, in which case compliance shall be deomonstrated by measuring the radiated emissions.
For FM (we do not get much coverage here), we operate under Title 47, Part 15.239: Operation in the band 88-108 MHz.
(a) Emissions from the intentional radiator shall be confined within a band 200 kHz wide centered on the operating frequency. The 200 kHz band shall lie wholly within the frequency range of 88-108 MHz.
(b) The field strength of any emissions within the permitted 200 kHz band shall not exceed 250 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.
(c) The field strength of any emissions radiated on any frequency outside of the specified 200 kHz band shall not exceed the general radiated emission limits in §15.209.
(d) A custom built telemetry intentional radiator operating in the frequency band 88-108 MHz and used for experimentation by an educational institute need not be certified provided the device complies with the standards in this part and the educational institution notifies the Office of Engineering and Technology, in writing, in advance of operation, providing the following information:
(1) The dates and places where the device will be operated;
(2) The purpose for which the device will be used;
(3) A description of the device, including the operating frequency, RF power output, and antenna; and,
(4) A statement that the device complies with the technical provisions of this part.
[54 FR 17714, Apr. 25, 1989; 54 FR 32340, Aug. 7, 1989; 80 FR 53750, Sept. 8, 2015]
For Carrier Current AM (the downtown transmitter) we operate under Title 47, Part 15.221:
15.221 Operation in the band 525-1705 kHz.
(a) Carrier current systems and transmitters employing a leaky coaxial cable as the radiating antenna may operate in the band 525-1705 kHz provided the field strength levels of the radiated emissions do not exceed 15 uV/m, as measured at a distance of 47,715/(frequency in kHz) meters (equivalent to Lambda/2Pi) from the electric power line or the coaxial cable, respectively. The field strength levels of emissions outside this band shall not exceed the general radiated emission limits in §15.209.
(b) As an alternative to the provisions in paragraph (a) of this section, intentional radiators used for the operation of an AM broadcast station on a college or university campus or on the campus of any other education institution may comply with the following:
(1) On the campus, the field strength of emissions appearing outside of this frequency band shall not exceed the general radiated emission limits shown in §15.209 as measured from the radiating source. There is no limit on the field strength of emissions appearing within this frequency band, except that the provisions of §15.5 continue to comply.
(2) At the perimeter of the campus, the field strength of any emissions, including those within the frequency band 525-1705 kHz, shall not exceed the general radiated emission in §15.209.
(3) The conducted limits specified in §15.207 apply to the radio frequency voltage on the public utility power lines outside of the campus. Due to the large number of radio frequency devices which may be used on the campus, contributing to the conducted emissions, as an alternative to measuring conducted emissions outside of the campus, it is acceptable to demonstrate compliance with this provision by measuring each individual intentional radiator employed in the system at the point where it connects to the AC power lines.
(c) A grant of equipment authorization is not required for intentional radiators operated under the provisions of this section. In lieu thereof, the intentional radiator shall be verified for compliance with the regulations in accordance with subpart J of part 2 of this chapter. This data shall be kept on file at the location of the studio, office or control room associated with the transmitting equipment. In some cases, this may correspond to the location of the transmitting equipment.
(d) For the band 535-1705 kHz, the frequency of operation shall be chosen such that operation is not within the protected field strength contours of licensed AM stations.