BLACK STAR METEOR 100 - Receiver Frequency Measurement; Maintenance and Repair

RECEIVER
FREOUENCY
MEASUREMENT
Direct measurement
of
received
frequency in
a superhet. receiver
is not norm-
ally
possible.
lt is
easier to measure the local
oscillator frequency
and allow for
any
l.
F. offsets.
For example,
a conventional receiver
with
455kHz l. F. and the
local
oscillator
set
high
would, when
tuned to
B. B.
C.
Radio
Three on 1.206MH2,
exhibit
a
measureable
local
oscillator frequency
of 1.661 MHz.
lf the l.F. fre-
quencies
are not
known, find
a station
of
known frequency
and
measure
the
local
oscillator.
Retune to
the unknown
station and measure
the local
oscillator
again.
The
difference between
the two measurements
is the
same as the dif-
ference
between
the
frequencies
of the two stations.
Some
modern multi-band,
multi-mode
receivers
use different
l.F.
frequencies
depending
on the band
selected which may render
this technique difficult
or
impractical.
Another method
is to tune in
the wanted
station then tune
a
signal
generator
-
feeding
a small
aerial
near
the
set
-
using
minimum
power,
until an audible
beat
with
the wanted
station is heard, then measure
the frequency
of
the
signal
generator.
By using low
power,
the chance
of spurious
beats, whistles or
'birdies'due
to harmonics
or
poor
image rejection in
the receiver,
is reduced.
The
two strongest
beats will normally
be at the wanted frequency
and
the
image frequency
(offset
by twice the
l.F.). The beat
at
the
wanted f requency
should be stronger
and
require
less injected
signal.
MAINTENANCE
AND
REPAIR
The manufacturer,
or the
appointed agents overseas,
will repair
and
calibrate
any
instrument
developing
a fault.
See the
guarantee
card for full
details but
always observe
the following
points:-
1. Remove
batteries
before returning
product
2. Do NOT return
any accessories.
3.
Pack
product
very carefully.
Whenever
possible
retain
original
packing
for this
purpose.
Where
owners wish
to undertake their
own repairs
and calibration. this
should
be carried
out by
skilled
personnel,
with
access to
precision
equipment,
working
in conjunction
with the
Service Manual which
can be
purchased
f
rom
the
manufacturer
or their overseas
aoents-