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1.1
SECTION
1
GENERAL
INFORMATION
General Description.
The
TFT
Model
7601
provides
digital
remote control
of
AM,
FM,
and
TV
transmitters.
Options incluae
an
SCA
Generator
and
Detector for use
with radio
or
TV
communications
links,
and
a
Status
Alarm
Option. These
options can
be
ordered with
the
Mode
l 7601,
in
which case they are
installed
at
the
factory;
or
they can
be
ordered
later
and
installed
by
the
customer in the
field.
1.1.1
Model
7601
Digital Telemetry/Control System.
This system
consists
of
a
Model
7601-C
unit
for use
at
the
control
site,
and
a
Model
7601-R
unit
for
use
at
the
remote
site.
The
two
units
may
be
linked
by
telephone wire
line
(TELCO)
or
by
STL
microwave or radio
(SCA).
The
system provides
10
channels
of
raise/lower
or
on/off
control ,
and
a
display
of
telemetry
from
the
remote
site
for each
of
the
10
channels.
The
Model
7601
alone
is
a
complete remote-control system.
However,
its
capabilities
can
be
increased
by
use
of
the
Status
Option described in Subsection 1.1
.2
.
Individual channels
are
selected
by
means
of
a
thumbwheel
switch
on
the
front
panel
of
the
7601-C.
Once
selected,
the
channel
number
is
sent
to
the
7601-R
to
select
the
channel
at
the
remote
point.
The
system addresses
this
channel
and
di~plays
the
meter reading
from
the remote
site
on
a front-pa~el 3
digit
telemetry display
on
the 7601-
C.
Meter readings are updated
three
times per second.
Control
commands
are
initiated
by
pushing
either
the
UP/ON
or
DOWN/OFF
button
on
the
front
panel.
When
a
command
is
activated
at
the
control
point,
a signal
is
fed
back
from
the remote
point.
This signal
verifies
receipt
of
the
command
by
illuminating
the
active
command
button.
To
ensure data accuracy
and
to
reduce the
possibility
of
operator
error,
each control
command
is
sent
twice.
The
two
are then
compared
at
the
remote
site,
bit
by
bit.
Only
if
they
match
exactly
are
the
commands
carried
out.
A control
failsafe
circuit
in
the
7601-R
monitors
reception
of
control
and
sync
bits,
and
if
these
bits
are
not received
for a period
of
20
to
55
seconds
(adjustable),
contacts
on
a
relay
open
to shut
down
the
transmitter.
These
relay
contacts
are
also
opened
by
a
power
failure
in
the
7601-R
.
A telemetry
failsafe
circuit
in
the
7601-C
monitors the
from
the
7601-R
and
produces a
hi
gh-1
evel
TTL
output
when
1-
