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

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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 plus-minus0.05  secs at 3.58 
MHz. The tolerance shall increase linearly to plus-minus0.1 
 sec down to 2.1 MHz, and remain at plus-minus0.1 
 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 plus-minus0.1  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 plus-minus1 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 plus-minus1 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,

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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, ))

[28 303 FR 13660 , Dec. 14, 1963]

    Editorial Note: For Federal Register citations affecting 
Sec. 73.687, see the List of CFR Sections Affected in the Finding Aids 
section of this volume.

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