[BC] Old FCC Audio Proof rules

[Harold Hallikainen]

>
> In a message dated 6/2/2006 11:04:38 PM Central Daylight Time,
> harold at hallikainen.com writes:
>
> I  remember running audio proofs on old RCA and Raytheon transmitters  and
> found they were flat down to 30Hz. The more modern transmitters I  was
> working with (Gates BC-1T and Bauer 707) were rolling off at 50Hz.
> Between
>
>
>
> *******************************
>
> Back in the old days didn't we have to do audio response measurments down
> to
> 30 Hz.?????
>
> I seemed to remember my old 50 kW. really flickering the floursecent tubes
> when I fired upo the 30 Hz. tone.    It was different in the slow
> oscillation
> when we hit the 50 kW. with 50 Hz.
>
> Seemed to recall they changed the audio prood rules way back there
> somewhere.
>
>
> Dave
>

Here's 73.47 from my 1980 copy of the rules (from the GPO). I first ran an
audio proof in 1970 or 1971, and I think these were the rules at that
time. Prior to that, though, they may have gone down to 30Hz. Interesting
typo is printed in paragraph (b) regarding where the report is to be
retained and how long...

Harold


73.47 Equipment performance measurements.
(a) The licensee of each AM station must make equip-
ment performance measurements for each main trans-
mitter when initially installed and thereafter at least
once each calendar year. One set of measurements must
be made during the 4-month period immediately preced-
ing the filing date of the application for renewal of the
station license. The dates of completion of successive
sets of measurements may be no more than I4 months
apart. If the same transmitter is authorized for more
than one mode of operation, equipment performance
measurements need be made at the highest authorized
power level. (Equipment performance measurements
for auxiliary transmitters are not required.) Equip-
ment performance mezmrements must be made with
equipment adjusted for normal program operation and
must include all circuits between the main studio micro-
phone terminals or amplifier input and the antenna cir-
cuit including equalizer or corrective circuits normally
used, but witbout compression. The measurement pro-
gram must yield the following information :
(1) Data and curves showing overall audiofrequency
response from 50 to 7,500 hertz (Hz) for approximately
25, 50, 35, and 100 (if obtainahle) percent modulation.
Family of curves should be plotted (one for each per-
centage above) with dB above and below a reference
frequency of 1,000 Hz as ordinate and audiofrequency
as abscissa.
(2) Data and curves showing audio frequency har-
monic content for 25, 50, 85, and 100 (if obtainable)
percent modulation for fundamental frequencies of 50,
100, 400, 1000, 5000, and 7500 Hz (either arithmetical
or root sum square values up to the tenth homonic or
10000 Hz). Plot family of curves (one for each per-
centage above) with percent distortion as ordinate and
audio frequency as abscissa.
(3) Data showing percentage of carrier amplitude-
regulation (carrier shift) for 25, 50, 85, and 100 (if
obtainable) percent modulation with 400 Hz tone.
(4) The carrier hum and extraneous noise level gen-
erated within the equipment, and measured throughout
the audio spectrum, or by bands, referred to the level
for 100 percent modulation of the carrier by a sinus-
oidal tone with a frequency of 400 Hz.
(5) Measurements or evidence showing that spuri-
ous radiations including radio frequency harmonics
are suppressed or are not present to a degree capable
of causing objectionable interference to other radio
services. Field strength measurements are preferred
but observations made with a communications type
receiver may be accepted. However, in particular
cases involving interference or controversy, the Com-
mission may require actual measurements.
(b) The data required by paragraph (a) of this
section, together with a description of instruments and
procedure, signed and dated by the qualified person
making the measurements, shall be kept on file at the
years, and on request shall be made available during
that time to any duly authorized representative of the
Federal Communication Commission.


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