§  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 § 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 µsecs at 3.58 MHz. The tolerance on the envelope
   delay shall be ±0.05 µsecs at 3.58 MHz. The tolerance shall increase
   linearly to ±0.1 µsec down to 2.1 MHz, and remain at ±0.1 µsec 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 µsec 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 § 73.682 and
   Figure 6 or 7 of § 73.699, as modified by vestigial sideband operation
   specified in Figure 5 of § 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 § 73.682 and
   Figure 6 or 7 of § 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, § 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, § 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 § 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 § 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
   § 73.1615 or § 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 § 73.687, see
   the List of CFR Sections Affected which appears in the Finding Aids
   section of the printed volume and on GPO Access.