HP 5254C Operating And Service Manual page 10

Section
III
Model 5254C
is
properly tuned and amplitude
of
INPUT
signal
is
adequate for
accurate frequency
measurement.
NOTE
Only
when the level indicator
meter
is
in the
green zone
will
the display count
be
valid.
3-13.
DOUBLE CHECKING
FREQUENCY
MEASUREMENT
RESULT.
3-14.
Because
of
the
heterodyne action
of
the
con-
verter,
frequency
measurement
results obtained
at
any one
setting
of the
Mixing Frequency Control
may
be
checked
at
other settings. In
most cases these
will
be
two consecutive responses: tune in the first
response and add
the
counter display
to
the dial
fre-
quency reading;
then tune up
in
frequency
to
the
sec-
ond response
and
subtract the counter display
from
the
dial
frequency reading (see
Table
3-2). In
some
cases there
will
be three consecutive
responses
(see
Figure
3-1); in
these
cases the third
response
will
be
the one
in
which you
subtract the
counter display
from
the
dial
frequency reading.
3-15.
A
counter reading
will
only be obtained
if
the
difference
frequency between
the
MIXING
FREQUENCY
and
the
INPUT
frequency
is
more
than
1
MHz
and less
than 53
MHz
(the
bandwidth
of
the
Video Amplifier
As-
sembly
A5).
3-16.
AID TO RAPID TUNING.
3-17.
When
using a counter with
MANUAL
START
it
is
easy
to
obtain
an indication
of
the
proper
MIXING
FREQUENCY
when
rapidly tuning the
Model 5254C
through
its
frequency range
in
search
of
an
unknown
INPUT
frequency. Set
FUNCTION
control
to
MANUAL
START.
This allows the counter to totalize
each
cycle
of
any difference
frequency produced during rapid
tuning.
When
the
counter display changes, indicating
that the
MIXING
FREQUENCY
is
heterodyning with the
INPUT
frequency and producing a difference frequency
within the
frequency range
of
the
basic counter, set
counter
FUNCTION
control to
FREQUENCY
and pro-
ceed
with
measurement.
Table 3-2.
Typical Double
-Check Frequency
Measurement
Input
Frequency
Counter Reading*
Mixing Frequency
Meter
Indication
Response
First
Response:
34567. 8
kHz
1.2
GHz Peak
1.2000000
GHz
+
345678
kHz
1.2345678
GHz
1.2345678
GHz
Second Response:
15432.
2
kHz
1.25
GHz
Peak
1.
2500000
GHz
-
154322
kHz
1.2345678
GHz
*
Counter
in
10
ms
Gate
to
give reading
in
kHz.
3-2