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Tebruary 14, 1931
G. 0. 97 EXPLA.INED
Inquiries received "by the National Association of Broadcasters indicate that many stations do not thoroly understand the application of General Order No. 97 which hecomes effective on April 30. The following explanatory note has been prepared by Eugene V. Cogley, assistant to the Managing Director of the NAB and former broadcast engineer of the Federal Radio Commission, as an answer to the inquiries received:
The best engineering minds in the country are in complete accord as to the really beneficial results that come to a transmitter which is equipped to give 100)o modulation. It not only means that eq,uipment so constructed will be more efficient in operation, but it also means that the coverage of these stations is going to be materially increased, under favorable circumstances. The in¬ crease in signal strength and the resulting betterment of conditions to the listener will go far to increase the usefulness of the station to the public.
It should be pointed out that the communication sent out by the Commission last week was only intended to bo effective as to the last renewal which was filed. Many stations to whom this letter was sent have filed applications for construction permits, or have already been granted permits, which when completed will allow them to be in complete accord with the terms of the order.
If there arc stations which will not be able to comply with this regulation
before April 30, the power of these stations will be reduced until the necessary
75'^ modulation can bo secured. This does not mean that the service area of these stations will be reduced. They will have the same coverage, as they are getting Y/ith their present transmitters, since the modulation increase will com¬ pensate the loss of output power. This was pointed out in the letter from the
Commission last week to those stations whose equipment at the time of the last renewal did not conform with the order, "The coverage factor in a station is a function of power and modulation, but the heterodyne interference depends on power alone and not changed by modulation,"
There was one point that was not made in that letter which is important to every station. That is the question of quota. If the Commission by the en?forcement of G. 0. 97 reduces the power of a 1 KW station to 500 watts, the quota for that state and zone would also be reduced by the difference in quota values o-s set out in G, 0. 92, or 0,4 unit. If the station now has a licensed power of 500 watts and is reduced to 250 watts then the quota would be decreased 0.2 unit. Under the existing provisions of General Order 102, this point would appear to be of vast importance to every stat@ and zone which is overquota.
In determining the operating power of a transmitter, the Commission uses the indirect method normally. This is arrived at by the measurement of the plate input power of the last radio stage. Then under the provisions of General Order 91 (for high level modulation, Section 111, and for low level Section IV) the antenna input power is computed from the plate input power by multiplying plate voltage by the plate current of the oscillator, or the last radio power amplifier, times the percentage specified.
There are two other methods which may be used to determine the operating