177 lines
4.5 KiB
Plaintext
177 lines
4.5 KiB
Plaintext
TWO SCANNER PATENTS
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by Bob Parnass, AJ9S
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Here is the information I published a few years ago about
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two of the scanner patents held by General Research Elec-
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tronics (GRE), makers of most Radio Shack scanners. You can
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find out this type of information by spending a few minutes
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in your corporate or academic law library.
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A Channel Lockout Invention
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Almost every model scanner sold today provides a way to
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bypass, or "lock out" channels from being scanned. It
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wasn't always this way. The first Bearcat scanner, a crys-
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tal controlled model with a row of red lights, had no
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lockout provision.
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On February 26, 1974, a U.S. patent was granted to a
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Japanese citizen for a "frequency skipping system" for scan-
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ning receivers. Patent 3,794,925 was granted to Kazuyoshi
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Imazeki, of Tokyo for a "Frequency-Skipping System for a
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Signal-Seeking Receiver."
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Filed almost two years earlier, Imazeki's development was
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described as a "switching network" operable "to cause the
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scanning circuit to skip those frequencies which the opera-
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tor does not want to monitor."
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The need for a lockout circuit was evident: "in some situa-
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tions the operator may not be interested in receiving one or
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more of the channels. Unless some provision is made for
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skipping these undesired channels, the system automatically
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tunes the receiver to them whereupon the operator must
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either listen to the undesired channel until it goes off the
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air or manually advance the receiver to the next channel."
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Earlier lockout schemes had drawbacks. The circuitry was
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"relatively complex and expensive" and had "the further
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disadvantage of requiring almost as much time to skip a
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channel as that required to tune to, and through, that chan-
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nel. In a system having ten or more channels of which only
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two or three are of interest to a particular operator, a
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relatively substantial amount of time is lost tuning through
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the 'skipped' channels."
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An example of this slower scheme was the way the Heathkit
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GR-110 scanner accomplished lockout, by merely providing a
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switch in series with each crystal.
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In Imazeki's scheme, an extra clock pulse was applied to the
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scanning counter circuit when a locked out channel was next
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in the scan sequence. This innovation allowed faster scan-
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ning of desired channels, by forcing the scanner to the next
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channel.
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The patent assignee is General Research of Electronics Inc.
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Priority Scanning Scheme
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It was 16 years ago last month that a U.S. patent was
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granted to a Japanese citizen for a priority scheme for
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scanning receivers. On April 2, 1974, patent 3,801,914 was
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granted to Kazuyoshi Imazeki, of Tokyo for a "Priority-
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Frequency System for a Signal-Seeking Receiver".
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Filed almost two years earlier, the system provided for a
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"signal seeking receiver to automatically tune" ... "to a
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priority signal whenever it is received. During non-
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priority receiver operation, a scanning circuit causes the
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receiver to automatically scan a plurality of predetermined
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frequencies and tune to a received signal have a frequency
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corresponding to one of the predetermined frequencies."
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In Imazeki's scheme, a low frequency priority oscillator
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periodically halts the scanner's clock circuit, interrupting
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the normal scan sequence. The priority oscillator's output
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is also connected through a multi-position switch, which
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allowed the user to designate an arbitrary channel as the
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priority channel.
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The circuit diagram in the patent looks familiar. That's
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because it forms the basis for the priority feature found in
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many crystal controlled scanners. The assignee is General
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Research of Electronics Inc.
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--
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============================================================================
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Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (708)979-541 |