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.