Congress chartered the National Research Council as a private and nonprofit institution to advise the federal government on issues of science, technology and health.
In 1980, the Department of Justice requested the National Research Council to review the methodology of BB&N and W&A. The council formed a Committee on Ballistic Acoustics, commonly known as the Ramsey Panel, who ignored the ballistic and acoustic evidence and reviewed technical aspects of the DPD radio system. This panel concluded:
"(iv) the conclusive acoustic evidence on the Dictabelt itself that the cross talk recordings were made through a radio receiver with automatic gain control (AGC). These different forms of evidence are all compatible with the recordings being made at the same time, and some are incompatible with the hypothesis of later superposed recordings by audio or direct electrical coupling."
The fundamental problem with this conclusion is the presented evidence does not show that the cross talk recordings were made through a radio receiver. Although the Committee on Ballistic Acoustics should have tested heterodynes for frequency modulation as conclusive evidence of the by-radio nature of the cross talk, they pursued fallacious arguments. In fact, a quantitative detail provided by the committee showed AGC acted on audio. Even worse, they concentrated on attack characteristics that are ambiguous evidence of AGC action and misinterpreted the decay characteristics, which showed AGC acted at two or more places within the system. Not surprising the Committee on Ballistic Acoustics began by confusing the subject that provided a technically correct method of showing by-radio nature of the cross talk.
"The by-radio nature of channel II cross talk is demonstrated by its detailed behavior in the presence of channel I heterodynes when another channel I transmitter is keyed on with a more powerful carrier signal. The frequency offset between the two carriers gives rise to a heterodyne tone in the channel I recording."
In all receivers the presence of two radio signals of nearly equal and different frequencies produce a beating of signals at an audio rate. The trigonometric identity for the addition of cosines (1) illustrates this process.
Cos (bt) + N Cos (ct) = (N-1) Cos (bt) + 2 Cos [(b-c) t/2 ] Cos [(b+c) t/2 ]
The N coefficient of the Cos (ct) term represents a radio signal whose amplitude is N times the other. Since the two radio frequencies, b and c, are nearly equal, the Cos [ (b-c ) t/2 ] term describes the only audio frequency. The absence of N as a factor preceding this audio term shows that the weaker of the two signals determines the amplitude of the heterodyne.
In a AM receiver, AGC action would reduce gain if N is much greater than one. Under these circumstances AGC action would decrease the strength of the weaker signal and proportionally reduce the amplitude of the heterodyne. Regardless of the value of N the heterodyne in a AM receiver would be a pure tone without harmonics.
When two radio signals beat within the earlier IF stages of a FM receiver the high gain of this amplifier levels the peaks of the cosine waveform. This saturation produces sloppy square waves. The limiter stage following the IF amplifier will remove any residual amplitude modulation unless the two radio signals have nearly the same amplitude. Under these circumstance the FM receiver produces a heterodyne that is rich in harmonics.
In a FM system as used by the DPD, cross talk modulates the frequency of the transmitter. When another station transmits concurrently and creates a heterodyne, its frequencies shift in accordance with changes in loudness of the cross talk at the transmitter. The Committee on Ballistic Acoustics ignored this simple and conclusive test of the by-radio nature of the cross talk.
Impervious to their oversight, the Committee on Ballistic Acoustics presented indisputable evidence of AGC action on audio. "However, the channel I receiver was fitted AGC to hold the output level approximately constant; as a result, the cross talk signals decrease in intensity in a few tens of milliseconds (as does any residual transmission from the original open microphone)."
Gain control circuits sample several cycles of the activating signal while changing gain. When radio signals activate AGC in receivers this adjustment requires microseconds and the limited bandwidth of the audio stages would stretch the response time to hundreds of microseconds. Cleary the explanation for the interval of tens of milliseconds lies elsewhere.
In a communications system, frequencies below one thousand hertz contain most of the audio power. Now a gain control circuit requires many and perhaps tens of milliseconds to sample a few cycles. Without doubt, the sluggish decrease in cross talk intensity conclusively demonstrates the by-audio nature of the change.
The Committee on Ballistic Acoustics mistakenly attributed every decrease in cross talk volumes to AGC actions in response to heterodynes.
In a FM system, received volume depends on the frequency deviation of the radio signal within the receiver. When a second station switches on, it beats with the first signal and halves the frequency deviation of the composite signal. This conclusion follows from the identity for the addition of cosines, where bt+m(t) replaces bt and N is set to one.
Cos [bt+m(t)] + Cos (ct) = 2 Cos [(bt+m(t)-ct )/2] Cos [(bt+m(t)+ct )/2]
When the second transmitter keys out, the frequency variation doubles and boasts power of the received audio by 6 decibel. In both cases, the limited bandwidth of audio stages stretch response time to hundreds of microseconds.
The multitude of signals on the five-minute Channel-I transmission gave astute investigators many opportunities to test this theoretical predication. Weiss and Aschkenasy reported:
"At 133 seconds after the start of the stuck-microphone transmission, the level of the noise drops by about 6 decibels (that is, to about one-fourth of its previous level). At almost the same moment a voice can be heard, communicating a brief but unintelligible message."
Since keying on of a second transmitter decreases the received audio of the first, this renders attack characteristics of AGC as inconclusive evidence, especially when magnitudes of the decreases are unreported.
The Committee on Ballistic Acoustics observed decay characteristics of AGC and noted:
"At the end of the channel I heterodyne, the AGC gradually increases the receiver gain, and signals on the open-microphone transmission increase in intensity in the recording."
Bolt Beranek and Newman , BB&N, provided details on the decay of AGC action. :
"In addition to having had similar effects on the waveforms recorded on Channel
1, the DPD recording shows evidence of a time constant in the 0.1 to 1.0 sec range. This AGC does not occur in any of the Motorola transmitters. It could, therefore, have been caused by the GE transmitter, by the receiver, or by the recorder."Two components, a resistor and a capacitor, determine the time constant of AGC decay. Generally manufacturers specify 10 percent tolerance on these parts. This means a nominal decay constant of 0.2 second may vary between 0.18 and
0.22 second from one piece of equipment to another. Clearly the finding of 1000 percent span of time constants showed AGC action occurred in more than circuit.Without doubt, the performance of the Committee on Ballistic Acoustics during their review of the acoustic evidence presented to the HSCA raises issues that transcend the assassination of President Kennedy.
Initially, Columbia University, Harvard University, the Lawrence Berkeley Laboratory, the Massachusetts Institute of Technology and its Lincoln Laboratory, Princeton University, Roll Laboratories, Trisolar Corporation, the Watson Research Center and Xerox Palo Alto Research Center lent their names and prestige to the report of the Committee on Ballistic Acoustics. These endorsements contributed toward corrupting the minds of two generations of assassination researchers.
Unlike the National Research Council whose charter by Congress and nonprofit status bestows a degree of immunity from civil actions, the suriving endorsers of the report are liable for their earlier actions and continued silence.
I call upon these endorsers to renounce their support of the Committee on Ballistic Acoustics.
Notes
- Derivation of the identity for the addition of cosines
Cos (X+Y) = Cos (X) Cos(Y) - Sin (X) Sin(Y) Cos (X-Y) = Cos (X) Cos(Y) + Sin (X) Sin(Y)
Adding the identities for the cosine of two angles gives
Cos (X+Y) + Cos(X-Y) = 2 Cos(X) Cos(Y)
Substituting X = (b+c) t/2 and Y = (b-c) t/2 produces
Cos (bt) + Cos (ct) = 2 Cos [(b-c) t/2] Cos [(b+c) t/2]
Adding (N-1) Cos (ct) to both sides of the above identity gives the desired result
Cos (bt) + N Cos (ct) = (N-1) Cos (ct) + 2 Cos [(b-c) t/2] Cos [(b+c) t/2]