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