"On Channel-II spectra we note that during voice transmissions there are no silence gaps between words. The signal level of Channel II is fairly constant. This could result from the presence of nearby motorcycle radios tuned to Channel II, while someone is transmitting on Channel II. A radio receiver close to a transmitting mike could form a closed loop having greater than unity gain. This will excite a natural frequency of the loop and it will act as an oscillator. The resulting oscillations will be recorded on the Channel-II recorder. We notice this phenomenon on Channel-II recording."
These oscillations overdrive amplifiers and produce distortion. Engineers limit this distortion by ensuring symmetrical clipping of the signal. Although this practice is not perfect, it makes the level of the second harmonic negligible. Hence manufacturers measure distortion in audio equipment by the level of the third harmonic and call it THD.
"During these periods, the spectra consist of a strong sinusoid (in the frequency range 1300-1800 Hz) and its harmonics. There is virtually no other signal present during these periods. We call these 'Brieftones.' Being high energy and very narrow-band, these are extremely valuable in determining the cross-talk level."
This paragraph provides two significant observations, namely "brieftones" occur when virtually no other signal is present and are narrow-band sinusoids.
"On Channel II spectra second harmonics of brieftones are quite prominent, while on Channel I spectra, all the Channel-II brieftones are present but their harmonics are not visible, indicating the limited frequency range of Channel I (even in the normal recording of Channel-I communications, the Channel-I recording has a similar roll-off at high frequencies.)."
Since brieftones have negligible second harmonics, the reported prominence show misidentification of signals. Further in a FM receiver, heterodynes have prominent second harmonics. (1) When simultaneous transmissions are silent, the heterodynes are narrow-band sinusoids. Of course the absence of audio accompanying these transmissions produce the illusion of no other station being present.
Mislabeling heterodynes as brieftones evaded an important issue. The observed constancy of the Channel-II heterodynes misnamed as brieftones show inactivity of AGC. However, some oscillographs of Channel-I show strong AGC response to heterodynes.
Coupling this unaddressed issue with the failure to report the itinerant AGC behavior of Channel-I, strongly suggests that recognition of the Barger and Bowles tapes of the Dictabelt as studio editions prompted the actions of the Ramsey Panel and the Watson Research Center.
Notes
1. The Ramsey Panel labeled many Channel-II signals with prominent second harmonics as brieftones. On the same page they show Channel-I heterodynes with prominent second harmonics.
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