Goto Section: 74.793 | 74.795 | Table of Contents
FCC 74.794
Revised as of December 4, 2012
Goto Year:2011 |
2013
§ 74.794 Digital emissions.
(a)(1) An applicant for a digital LPTV or TV translator station
construction permit shall specify that the station will be constructed
to confine out-of-channel emissions within one of the following
emission masks: Simple, stringent or full service.
(2) The power level of emissions on frequencies outside the authorized
channel of operation must be attenuated no less than following amounts
below the average transmitted power within the authorized 6 MHz
channel. In the mask specifications listed in § 74.794(a)(2) and
(a)(3), A is the attenuation in dB and Δf is the frequency difference
in MHz from the edge of the channel.
(i) Simple mask. At the channel edges, emissions must be attenuated no
less than 46 dB. More than 6 MHz from the channel edges, emissions must
be attenuated no less than 71 dB. At any frequency between 0 and 6 MHz
from the channel edges, emissions must be attenuated no less than the
value determined by the following formula:
A (dB) = 46 + (Δf2 /1.44)
(ii) Stringent mask. In the first 500 kHz from the channel edges,
emissions must be attenuated no less than 47 dB. More than 3 MHz from
the channel edges, emissions must be attenuated no less than 76 dB. At
any frequency between 0.5 and 3 MHz from the channel edges, emissions
must be attenuated no less than the value determined by the following
formula:
A(dB) = 47 + 11.5 (Δf-0.5)
(iii) Full service mask: (A) The power level of emissions on
frequencies outside the authorized channel of operation must be
attenuated no less than the following amounts below the average
transmitted power within the authorized channel. In the first 500 kHz
from the channel edge the emissions must be attenuated no less than 47
dB. More than 6 MHz from the channel edge, emissions must be attenuated
no less than 110 dB. At any frequency between 0.5 and 6 MHz from the
channel edge, emissions must be attenuated no less than the value
determined by the following formula:
Attenuation in dB = −11.5([Delta]f + 3.6);
Where:
[Delta] f = frequency difference in MHz from the edge of the channel.
(B) This attenuation is based on a measurement bandwidth of 500 kHz.
Other measurement bandwidths may be used as long as appropriate
correction factors are applied. Measurements need not be made any
closer to the band edge than one half of the resolution bandwidth of
the measuring instrument. Emissions include sidebands, spurious
emissions and radio frequency harmonics. Attenuation is to be measured
at the output terminals of the transmitter (including any filters that
may be employed). In the event of interference caused to any service,
greater attenuation may be required.
(3) The attenuation values for the simple and stringent emission masks
are based on a measurement bandwidth of 500 kHz. Other measurement
bandwidths may be used and converted to the reference 500 kHz value by
the following formula:
A(dB) = Aalternate + 10 log (BWalternate / 500)
where A(dB) is the measured or calculated attenuation value for the
reference 500 kHz bandwidth, and Aalternate is the measured or
calculated attenuation for a bandwidth BWalternate . Emissions include
sidebands, spurious emissions and radio harmonics. Attenuation is to be
measured at the output terminals of the transmitter (including any
filters that may be employed). In the event of interference caused to
any service by out-of-channel emissions, greater attenuation may be
required.
(b) In addition to meeting the emission attenuation requirements of the
simple or stringent mask (including attenuation of radio frequency
harmonics), digital low power TV and TV translator stations authorized
to operate on TV channels 22-24, (518-536 MHz), 32-36 (578-608 MHz), 38
(614-620 MHz), and 65-69 (776-806 MHz) must provide specific “out of
band” protection to Radio Navigation Satellite Services in the bands:
L5 (1164-1215 MHz); L2 (1215-1240 MHz) and L1 (1559-1610 MHz).
(1) An FCC-certificated transmitter specifically certified for use on
one or more of the above channels must include filtering with an
attenuation of not less than 85 dB in the GPS bands, which will have
the effect of reducing harmonics in the GPS bands from what is produced
by the digital transmitter, and this attenuation must be demonstrated
as part of the certification application to the Commission.
(2) For an installation on one of the above channels with a digital
transmitter not specifically FCC-certificated for the channel, a low
pass filter or equivalent device rated by its manufacturer to have an
attenuation of at least 85 dB in the GPS bands, which will have the
effect of reducing harmonics in the GPS bands from what is produced by
the digital transmitter, and must be installed in a manner that will
prevent the harmonic emission content from reaching the antenna. A
description of the low pass filter or equivalent device with the
manufacturer's rating or a report of measurements by a qualified
individual shall be retained with the station license. Field
measurements of the second or third harmonic output of a transmitter so
equipped are not required.
[ 69 FR 69336 , Nov. 29, 2004, as amended at 76 FR 44828 , July 27, 2011]
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Goto Section: 74.793 | 74.795
Goto Year: 2011 |
2013
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