Television digest with electronics reports (Jan-Dec 1953)

than —20 db for a modulating frequency of 4.75 me or greater. 28 2Sa (4) 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 29 to establish peak output voltage plus a variable frequency sine wave voltage occupying the interval between sychronizing pulses. 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 of 0.75 of peak output voltage. The amplitude of the 200 kilocycle 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. (5) 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 me, of zei’o microseconds up to a frequency of 3.0 me and then linearly decreasing to 4.18 me so as to be equal to —0.17 microseconds at 3.58 me. The tolerance on the envelope delay shall be ± 0.05 microseconds at 3.58 me. The tolerance shall increase linearly to ±. 0.1 microseconds, down to 2.1 me, and remain at 28 Field strength measurements are desired. It is anticipated that these may not yield data which are consistent enough to prove compliance with the attenuation standards prescribed above. In that case, measurements with a dummy load of pure resistance, together with data on the antenna characteristics, shall be taken in place of over-all field measurements. '■x* Television stations shall have until July 1, 1954 for compliance with the requirements of this subparagraph with respect to attenuation of the upper sidebands. 29 The “synchronizing signal” referred to in this section means either a standard synchronizing wave form or any pulse that will properly set the peak. ± 0.1 microseconds down to 0.2 me. "* The tolerance shall also increase linearly to ± 0.1 microseconds at 4.18 me. (6) The radio frequency signal, as radiated, shall have an envelope as would be produced by a modulating signal in conformity with Appendix III, Figure 4(a) or (b), as modified by vestigial sideband operation specified by Appendix III, Figure 3. (7) The time interval between the leading edges of successive horizontal pulses shall vary less than one half of one per cent of the average interval, however, for color transmissions, § 3.682(a)(5) and § 3.682(a)(6) shall be controlling. (8) 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 per cent 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, § 3.682(a) (5) and § 3.682(a) (6) shall be controlling. (9) Sufficient monitoring equipment shall be employed to determine whether the visual signal complies with the requirements of this subpart. (10) For color transmission the transfer characteristic (that is the relationship between the transmitter RF output and video signal input) shall be substantially linear between the reference black and reference white levels. B. Delete subparagraph (c)(1) of §3.687 and substitute the following: (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 one kilocycle of the authorized frequency; automatic means shall be provided in the aural transmitter to maintain the carrier frequency within four kilocycles of the assigned aural carrier frequency or, alternatively, 4.5 megacycles above the actual visual carrier frequency within five kilocycles. For color transmission the aural carrier shall be maintained 4.5 megacycles above the visual carrier within ± 1 kilocycle. When required by § 3.606, the visual and aural carrier frequencies are to be offset in frequency by 10 kilocycles (plus or minus, as indicated) from the normal carrier frequencies. IV. Appendix III to subpart E is amended as follows: Delete Figures 3, 4, and 7 and add the attached Figures 3, 4(a), 4(b), 4(c), and 7. 28,1 Tolerances for the interval of 0.0 to 0.2 me are not specified at the present time. 13