Eddystone 990R - Page 25

External
drive
is therefore
required
throughout
the
band
37.7-257.7
MHz
for
recep-
tion
of
all
signal
frequencies
27-240 MHz.
This
assumes
that
harmonic
operation
using
the
internal
frequency
multiplication
facility
is
not
feasible,
perhaps
because
of
the
increased
spacing
between
the
discrete
synthesiser
output
ohannels
which
would
result.
If
this
problem
does
not
arise,
the
upper
frequency
requirement
is
reduced
to
83.56
MHz
since
multiplication
by
factors
of
2
or
3
is
available.
Calculation
of
the
required
drive
frequency
is carried
out
in the
same
manner
as
when
working
out
crystal
freq-
uencies
for
internal
crystal
control.
"
1
When
using
the
receiver
with
external
frequency
control,
the
SYSTEM
SWITCH
must
be
set
to "EXT",
the
TUNING
and RANGE
SWITCH
being
operated
as for
crystal
control.
Operation
with
EP17R
Panoramic
Display
Unit
.
Reference
should
be
made
to
the
Manual
supplied
with
the
Display
Unit
for
instruc-
tions
on
initial
adjustment
etc.
(see
page
9
onwards).
On
page
11,
ignore
all
refer-
ences
to
the 770R
(Mk.Il)
VHP
Receiver
and
read
instead
the
notes
on
the
EPR25
Install-
ation
since
these
are
applicable
also
to
the
EPR30
(990R
+ EPI7R)
,
except
that
the
calibrator
has
a fundamental
of 10
MHz.
It
should
be
noted
that
in
reading
page
12
of
the
EP17R
Manual,
the
lowest
display
frequency
when
using the
990R
Receiver
with
an
EPI7R,
occurs
at
the
left-hand
end
of
the
trace.
This
is due
to
there
being
two
frequency
inversions,
one
in
the
receiver
itself
and
the
other
in the IP
Converter
which
provides
the
5.2
MHz
output
to
drive
the
Display
Unit,
Interpolation
can be
carried
out
as
described
for the
TJOR
Receiver
provided
that
an
external
1
MHz
harmonic
generator
is
available.
Output
from
the
receiver
to the
IP
Converter
can
be
taken
either
from
the
low-level
output
in
the
collector
of
the
Mixer
Stage
or
from
the
high-level
output
via
the
emitter
follower
TRIG.
The
available
bandwidth
is
greater
at
the
low-level
output
since
this
is
taken
ahead
of
the
10.
7
Bfflz
filters.
A
width
of
approximately
1
MHz
is
available
at ^the
higher
frequencies
in
the
tuning
range.
The
setting
of
the
panel
SELECTIVITY
S'
'ITCH
determines
the
bandwidth
available
at
the
high-level
output.
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24
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