Goto Section: 73.686 | 73.688 | Table of Contents
FCC 73.687
Revised as of October 1, 2008
Goto Year:2007 |
2009
Sec. 73.687 Transmission system requirements.
(a) Visual transmitter. (1) The field strength or voltage of the lower
sideband, as radiated or dissipated and measured as described in paragraph
(a)(2) of this section, shall not be greater than −20 dB for a modulating
frequency of 1.25 MHz or greater and in addition, for color, shall not be
greater than −42 dB for a modulating frequency of 3.579545 MHz (the color
subcarrier frequency). For both monochrome and color, the field strength or
voltage of the upper sideband as radiated or dissipated and measured as
described in paragraph (a)(2) of this section shall not be greater than −20
dB for a modulating frequency of 4.75 MHz or greater. For stations operating
on Channels 15–69 and employing a transmitter delivering maximum peak visual
power output of 1 kW or less, the field strength or voltage of the upper and
lower sidebands, as radiated or dissipated and measured as described in
paragraph (a)(2) of this section, shall depart from the visual amplitude
characteristic (Figure 5a of Sec. 73.699) by no more than the following amounts:
−2 dB at 0.5 MHz below visual carrier frequency;
−2 dB at 0.5 MHz above visual carrier frequency;
−2 dB at 1.25 MHz above visual carrier frequency;
−3 dB at 2.0 MHz above visual carrier frequency;
−6 dB at 3.0 MHz above visual carrier frequency;
−12 dB at 3.5 MHz above visual carrier frequency;
−8 dB at 3.58 MHz above visual carrier frequency (for color transmission
only).
The field strength or voltage of the upper and lower sidebands, as radiated
or dissipated and measured as described in paragraph (a)(2) of this section,
shall not exceed a level of −20 dB for a modulating frequency of 4.75 MHz or
greater. If interference to the reception of other stations is caused by
out-of-channel lower sideband emission, the technical requirements
applicable to stations operating on Channels 2–13 shall be met.
(2) The attenuation characteristics of a visual transmitter shall be
measured by application of a modulating signal to the transmitter input
terminals in place of the normal composite television video signal. The
signal applied shall be a composite signal composed of a synchronizing
signal to establish peak output voltage plus a variable frequency sine wave
voltage occupying the interval between synchronizing pulses. (The
“synchronizing signal” referred to in this section means either a standard
synchronizing wave form or any pulse that will properly set the peak.) The
axis of the sine wave in the composite signal observed in the output monitor
shall be maintained at an amplitude 0.5 of the voltage at synchronizing
peaks. The amplitude of the sine wave input shall be held at a constant
value. This constant value should be such that at no modulating frequency
does the maximum excursion of the sine wave, observed in the composite
output signal monitor, exceed the value 0.75 of peak output voltage. The
amplitude of the 200 kHz sideband shall be measured and designated zero dB
as a basis for comparison. The modulation signal frequency shall then be
varied over the desired range and the field strength or signal voltage of
the corresponding sidebands measured. As an alternate method of measuring,
in those cases in which the automatic d-c insertion can be replaced by
manual control, the above characteristic may be taken by the use of a video
sweep generator and without the use of pedestal synchronizing pulses. The
d-c level shall be set for midcharacteristic operation.
(3) A sine wave, introduced at those terminals of the transmitter which are
normally fed the composite color picture signal, shall produce a radiated
signal having an envelope delay, relative to the average envelope delay
between 0.05 and 0.20 MHz, of zero microseconds up to a frequency of 3.0
MHz; and then linearly decreasing to 4.18 MHz so as to be equal to −0.17
secs at 3.58 MHz. The tolerance on the envelope delay shall be 0.05 secs
at 3.58 MHz. The tolerance shall increase linearly to 0.1 sec down to 2.1
MHz, and remain at 0.1 sec down to 0.2 MHz. (Tolerances for the interval
of 0.0 to 0.2 MHz are not specified at the present time.) The tolerance
shall also increase linearly to 0.1 sec at 4.18 MHz.
(4) The radio frequency signal, as radiated, shall have an envelope as would
be produced by a modulating signal in conformity with Sec. 73.682 and Figure 6
or 7 of Sec. 73.699, as modified by vestigial sideband operation specified in
Figure 5 of Sec. 73.699. For stations operating on Channels 15–69 the radio
frequency signal as radiated, shall have an envelope as would be produced by
a modulating signal in conformity with Sec. 73.682 and Figure 6 or 7 of Sec. 73.699.
(5) The time interval between the leading edges of successive horizontal
pulses shall vary less than one half of one percent of the average interval.
However, for color transmissions, Sec. 73.682(a) (5) and (6) shall be
controlling.
(6) The rate of change of the frequency of recurrence of the leading edges
of the horizontal synchronizing signals shall be not greater than 0.15
percent per second, the frequency to be determined by an averaging process
carried out over a period of not less than 20, nor more than 100 lines, such
lines not to include any portion of the blanking interval. However, for
color transmissions, Sec. 73.682(a) (5) and (6) shall be controlling.
(b) Aural transmitter. (1) Pre-emphasis shall be employed as closely as
practicable in accordance with the impedance-frequency characteristic of a
series inductance-resistance network having a time constant of 75
microseconds. (See upper curve of Figure 12 Sec. 73.699.)
(2) If a limiting or compression amplifier is employed, precaution should be
maintained in its connection in the circuit due to the use of pre-emphasis
in the transmitting system.
(3) Aural modulation levels are specified in Sec. 73.1570.
(c) Requirements applicable to both visual and aural transmitters. (1)
Automatic means shall be provided in the visual transmitter to maintain the
carrier frequency within 1 kHz of the authorized frequency; automatic means
shall be provided in the aural transmitter to maintain the carrier frequency
4.5 MHz above the actual visual carrier frequency within 1 kHz.
(2) The transmitters shall be equipped with suitable indicating instruments
for the determination of operating power and with other instruments
necessary for proper adjustment, operation, and maintenance of the
equipment.
(3) Adequate provision shall be made for varying the output power of the
transmitters to compensate for excessive variations in line voltage or for
other factors affecting the output power.
(4) Adequate provisions shall be provided in all component parts to avoid
overheating at the rated maximum output powers.
(d) The construction, installation, and operation of broadcast equipment is
expected to conform with all applicable local, state, and federally imposed
safety regulations and standards, enforcement of which is the responsibility
of the issuing regulatory agency.
(e) Operation. (1) Spurious emissions, including radio frequency harmonics,
shall be maintained at as low a level as the state of the art permits. As
measured at the output terminals of the transmitter (including harmonic
filters, if required) all emissions removed in frequency in excess of 3 MHz
above or below the respective channel edge shall be attenuated no less than
60 dB. below the visual transmitted power. (The 60 dB. value for television
transmitters specified in this rule should be considered as a temporary
requirement which may be increased at a later date, especially when more
higher-powered equipment is utilized. Stations should, therefore, give
consideration to the installation of equipment with greater attenuation than
60 dB.) In the event of interference caused to any service greater
attenuation will be required.
(2) If a limiting or compression amplifier is used in conjunction with the
aural transmitter, due operating precautions should be maintained because of
pre-emphasis in the transmitting system.
(3) TV broadcast stations operating on Channel 14 and Channel 69 must take
special precautions to avoid interference to adjacent spectrum land mobile
radio service facilities. Where a TV station is authorized and operating
prior to the authorization and operation of the land mobile facility, a
Channel 14 station must attenuate its emissions within the frequency range
467 to 470 MHz and a Channel 69 station must attentuate its emissions within
the frequency range 806 to 809 MHz if necessary to permit reasonable use of
the adjacent frequencies by land mobile licensees.
(4) The requirements listed below apply to permittees authorized to
construct a new station on TV Channel 14 or TV Channel 69, and to licensees
authorized to change the channel of an existing station to Channel 14 or to
Channel 69, to increase effective radiated power (ERP) (including any change
in directional antenna characteristics that results in an increase in ERP in
any direction), or to change the transmitting location of an existing
station.
(i) For the purposes of this paragraph, a protected land mobile facility is
a receiver that is intended to receive transmissions from licensed land
mobile stations within the frequency band below 470 MHz (as relates to
Channel 14) or above 806 MHz (as relates to Channel 69), and is associated
with one or more land mobile stations for which a license has been issued by
the Commission, or a proper application has been received by the Commission
prior to the date of the filing of the TV construction permit application.
However, a land mobile facility will not be protected if it is proposed in
an application that is denied or dismissed and that action is no longer
subject to Commission review. Further, if the land mobile station is not
operating when the TV facility commences operation and it does not commence
operation within the time permitted by its authorization in accordance with
part 90 of this chapter, it will not be protected.
(ii) A TV permittee must take steps before construction to identify
potential interference to normal land mobile operation that could be caused
by TV emissions outside the authorized channel, land mobile receiver
desensitization or intermodulation. It must install filters and take other
precautions as necessary, and submit evidence that no interference is being
caused before it will be permitted to transmit programming on the new
facilities pursuant to the provisions of Sec. 73.1615 or Sec. 73.1620 of this part.
A TV permittee must reduce its emissions within the land mobile channel of a
protected land mobile facility that is receiving interference caused by the
TV emission producing a vertically polarized signal and a field strength in
excess of 17 dBu at the land mobile receiver site on the land mobile
frequency. The TV emission should be measured with equipment set to a 30 kHz
measurement bandwidth including the entire applicable land mobile channel. A
TV permittee must correct a desensitization problem if its occurrence can be
directly linked to the start of the TV operation and the land mobile station
is using facilities with typical desensitization rejection characteristics.
A TV permittee must identify the source of an intermodulation product that
is generated when the TV operation commences. If the intermodulation source
is under its control, the TV permittee must correct the problem. If the
intermodulation source is beyond the TV permittee's control, it must
cooperate in the resolution of the problem and should provide whatever
technical assistance it can.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, 1068, 1082 (47 U.S.C. 154,
155, 303))
[ 28 FR 13660 , Dec. 14, 1963]
Editorial Note: ForFederal Registercitations affecting Sec. 73.687, see the
List of CFR Sections Affected which appears in the Finding Aids section of
the printed volume and on GPO Access.
Goto Section: 73.686 | 73.688
Goto Year: 2007 |
2009
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