Sec. 74.936  Emissions and bandwidth.

    (a) An instrutional television fixed station shall normally employ 
amplitude modulation (A5) for the transmission of the visual signal and 
frequency modulation (F3) for the transmission of the aural signal.
    (b) On or after November 1, 1991, the maximum out-of-band power of a 
transmitter operating in this service shall be attenuated 38 dB relative 
to the peak visual carrier at the channel edges and constant slope 
attenuation from this level to 60 dB relative to the peak visual carrier 
at 1 MHz below the lower band edge and 0.5 MHz above the upper band 
edge. All out-of-band emissions extending beyond these frequencies shall 
be attenuated at least 60 dB below the peak visual carrier power. 
However, should interference occur as a result of emissions outside the 
assigned channel, additional attenuation may be required. A transmitter 
licensed prior to November 1, 1991, that remains at the station site 
initially licensed, and does not comply with this paragraph, may 
continue to be used for its life if it does not cause harmful 
interference to the operation of any other licensee. Any non-conforming 
transmitter replaced after November 1, 1991, shall be replaced by a 
transmitter meeting the requirements of this paragraph.
    (c) The requirements of Sec. 73.687(c)(2) of this chapter will be 
considered to be satisfied insofar as measurements of

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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 Sec. 74.935 of this part. Measurements of 
the separate visual and aural operating powers must be made at 
sufficiently frequent intervals to insure compliance with the rules, and 
in no event less than once a month.
    (d) As a further exception to the other requirements of this 
section, transmitting equipment characteristics may vary from these 
requirements to the extent necessary to insure that transmitted 
information is not likely to be received in intelligible form by 
unauthorized subscribers or licensees, provided such variations permit 
recovery of the transmitted information without perceptible degradation 
as compared to the same information transmitted without such variations.

[ 28 FR 13731 , Dec. 14, 1963, as amended at  55 FR 46014 , Oct. 31, 1990]