Sec. 73.687 of this chapter regarding the installation and performance 
of television broadcast transmitters and associated equipment shall 
apply to instructional television fixed stations.
    (b) The overall attenuation characteristics of the transmitter may 
vary from those specified in Sec. 73.687 of this chapter, provided that 
the provisions of Sec. 74.936 of this part are met. However, care should 
be exercised in the adjustment of the transmitter to insure correct 
overall response of the transmitter for proper transmission of the upper 
and vestigial lower sideband.
    (c) The provisions of Sec. 74.961 in lieu of Sec. 73.687(c)(1) of 
this chapter apply with respect to the frequency tolerance for the 
visual carrier.
    (d) The provisions of Sec. 74.936 in lieu of Sec. 73.687(i)(1) of 
this chapter apply with respect to spurious emissions and radio 
frequency harmonics.
    (e) The requirements of Sec. 73.687(c)(2) of this chapter will be 
considered to be met insofar as measurements of operating power are 
concerned, if the transmitter is equipped with instruments for 
determining the combined visual and aural operating power. However, 
licensees are expected to maintain the operating powers within the 
limits specified in the rules of this part. Measurements of the separate 
visual and aural operating powers should be made at sufficiently 
frequent intervals to ensure compliance with the rules.
    (f) Transmitting apparatus (translators and boosters) used solely 
for relaying signals received from other ITFS stations and operating in 
the manner described in Sec. 74.934(a)(2) shall meet the following 
requirements before being type accepted by the Commission.
    (1) The frequency converter and associated amplifiers shall be so 
designed that the electrical characteristics of a standard television 
signal introduced into the input terminals will not be significantly 
altered by passage through the apparatus except as to frequency and 
amplitude. The overall response of the apparatus within its assigned 
channel when operating at its rated power output and measured at the 
output terminals, shall provide a smooth curve, varying within limits 
separated by no more than 4 dB: Provided, however, That means may be 
provided to reduce the amplitude of the aural carrier below those 
limits, if necessary to prevent intermodulation which would mar the 
quality of the retransmitted picture or result in emissions outside of 
the assigned channel.
    (2) The suppression of emissions appearing outside of the assigned 
channel shall comply with Sec. 74.936(b) and (c).
    (3) The local oscillator employed in the frequency converter shall 
maintain its operating frequency within 0.02 percent of its rated 
frequency when subjected to variations in ambient temperature between 
minus 30 deg. and plus 50 deg. centigrade and variations in powerline 
voltage between 85 percent and 115 percent of the rated supply voltage.
    (4) The apparatus shall contain automatic circuits which will 
maintain peak visual power output constant within 2 dB when the strength 
of the input signal is varied over a range of 30 dB and which will not 
permit the peak visual power output to exceed the maximum rated power 
output under any conditions. If a manual adjustment is provided to 
compensate for different average signal strengths, provision shall be 
made for determining the proper setting for the control. If improper 
adjustment of the control could result in improper operation a label 
bearing a suitable warning shall be affixed at the adjustment control: 
Provided, however, That apparatus with an output of 50 milliwatts peak 
visual power per channel or less need not comply with this paragraph, 
provided the equipment is so designed that the rated output power of the 
transmitter cannot be exceeded by more than 3 dB by an increase in the 
input signal.
    (5) The apparatus shall be equipped with automatic controls which 
will place it in a nonradiating condition when no signal is being 
received on the input channel, either due to absence of a transmitted 
signal or failure of the receiving portion of the relay transmitter. In 
the case of equipment (translators or boosters) of 50 milliwatts peak 
visual power per channel or less relaying more than one channel it shall 
be turned off in the absence of the last signal to be relayed. The 
automatic

[[Page 469]]

control may include a time delay feature to prevent interruptions in the 
operation of the relay transmitter caused by fading or other momentary 
failures of the incoming signal.
    (6) The tube(s) or transistor(s) employed in the final radio 
frequency amplifier shall be of the appropriate power rating to provide 
the rated power output of the relay transmitter. The normal operating 
constants for operation at the rated power output shall be specified. 
The apparatus shall be equipped with suitable meters or meter jacks so 
that appropriate voltage and current measurements may be made while the 
apparatus is in operation.
    (7) Boosters used in this service shall comply with all the 
provisions of this paragraph except with paragraph (f)(3). However, in 
addition, the isolation between the input and output circuits of the 
booster, including the receiving and transmitting antenna systems shall 
be at least 20 dB greater than the maximum overall gain of the booster 
amplifier. Boosters may use opposite antenna polarization of the input 
and output antennas.

[ 28 FR 13731 , Dec. 14, 1963, as amended at  36 FR 8873 , May 14, 1971;  48 FR 44807 , Sept. 30, 1983;  55 FR 46014 , Oct. 31, 1990]