Re: How could they have been so wrong?

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Date: Sat, 21 Aug 2004 03:28:08 GMT

Yes- this makes much sense- thanks for unraveling the stinking mess.

Herbert Blenner wrote:
> 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
>
> 1. 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]
>
>
>
>
>

• Previous message: Jonathan Kirwan: "Re: Offset voltage on voltage follower"
• In reply to: Herbert Blenner: "How could they have been so wrong?"
• Next in thread: Ken Taylor: "Re: How can they be such wankers?"
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