RADIOMETER BKF10, Operating Instructions Manual

Page: 3 / 8

2. Set the controls of the BKF10 as fol­
lows:
INPUT FILTER: FLAT
MAX. INPUT:
To suit output level from device
under test. (10 mV to 3 V or 100 mV
to 30 V.)
VERNIER: CAL.
LEVEL CONTROL switch (16):
To suit output or input level of the
device under test.
LEVEL AT:
A) INPUT (of BKF10), if a constant
output from the device under
test is required.
B) OUTPUT (of BKF10), if a constant
input to the device under test is
required.
Oscillator function switch (8): MAN.
OUTPUT FREQ. control (18):
To indicate, say, 1 kHz on INPUT
FREQUENCY meter.
3. Check that neither OUT OF RANGE
lamp lights.
4.
Set oscillator function switch (8) to
SINGLE SWEEP and momentarily de­
press the SINGLE SWEEP button (7).
This starts the automatic sweep func­
tion.
The BKF10 sweeps
downwards
in fre­
quency from 20 kHz to 20 Hz. When
the sweep is completed (about 60
seconds) the BKF10 will reset automat­
ically in readiness for the next sweep.
The single sweep function may be
stopped at any time during a sweep by
simply setting the oscillator function
switch (8) to the MAN. position, which
may then be reset to SINGLE SWEEP
by repeating item
(4).
5. During the sweep the three meters
show simultaneously:
INPUT FREQUENCY meter:
The frequency at which the measure­
ments are being made.
DISTORTION meter:
The total harmonic distortion at the
frequency indicated by the Input
Frequency meter. (Harmonics mea­
sured, 10 Hz to 150 kHz).
INPUT/OUTPUT RATIO meter:
The input/output ratio of the device
under test at the frequency indicat­
ed by the Input Frequency meter.
SIGNAL-TO-NOISE RATIO
MEASUREMENTS
Signal-to-noise measurements are made by
depressing the SIN button (13) on the
front panel. The bandwidth of the signal­
to-noise measurements is 10 Hz to 150
kHz. Depressing the SIN button holds the
ALC pre-amplifier gain constant while at
the same time muting the oscillator. A dc
analogue output of the SIN measurements
is available as long as the SIN button is
held depressed. Facilities for external con­
trol of the SIN function are available at
the multiconnector (28). See page 5 for
details.
INPUT/OUTPUT RATIO MEASUREMENTS
Input/output ratios are indicated on the
linear dB scale of the INPUT/OUTPUT
RATIO meter.
The INPUT/OUTPUT �I\TIO meter is pro­
vided with two indicator lamps, "-dB" (4)
and " +20 dB" (6), which function as fol­
lows:
-dB Lamp
(4)
When a negative dB value or loss occurs
in a device under test, the -dB lamp will
light and the value indicated on the meter
will represent the loss directly in dB.
+ 20 dB Lamp (6)
When the MAX. INPUT switch is set to the
30 V position, a 20 dB attenuator is con­
nected into the input circuit of the BKF10.
This will result in a 20 dB lower reading
on the INPUT/OUTPUT RATIO meter and
on the associated recorder output. As a
reminder, the " + 20 dB" lamp lights when­
ever the MAX. INPUT switch is set to
"30 V". The operator then adds +20 dB
to the INPUT/OUTPUT RATIO reading and
the recorded level.
If the LEVEL AT switch is at INPUT, the
actual INPUT voltage of BKF10 is
10 times
(20
dB) that indicated by the LEVEL CON­
TROL switch (16).
Example:
MAX. INPUT switch is at "30 V", the
"-dB" and " +20 dB" lamps are lit, and
the meter reads 7 dB. Then the true IN­
PUT/OUTPUT ratio is: -7 dB + 20 dB
=
+13 dB.
OUT -OF-RANGE LAMPS
a. If the INPUT out-of-range lamp lights,
check MAX. INPUT switch setting. This
will occur if the input level to the
BKF10 is either too high or too low.
b. If the OUTPUT out-of-range lamp lights,
check the settings of the level control
switch (16), VERNIER (15) and LEVEL
AT switch (17).
c. If both out-of-range lamps light, this
normally indicates that either there is
no signal path through the device un­
der test (LEVEL AT switch at INPUT
only) or the output level from the device
under test is inadequate for making
measurements.
d. If either of the out-of-range lamps
lights, for example, during a sweep,
check the characteristics of the device
under test. This can be the case partic­
ularly where measurements are made
at a constant output from the device
under test (LEVEL AT switch (17) set
to INPUT), and where its characteristics
prevent the B
' KF10 from delivering an
output level sufficient to maintain the
constant output required from the de­
vice under test.
HIGH-PASS AND LOW-PASS FILTERS
250 HZ
Fig. 3. Characteristics of the LP/HP-filters.
1. To eliminate the effects of hum and
noise below 250 Hz, set the INPUT
FILTER (2) switch to HP. Note that
only fundamental frequencies above
250 Hz are relevant.
2. To measure distortion due to hum and
noise below 250 Hz, set the INPUT
FILTER switch to LP. If the funda­
mental frequency is above 500 Hz, the
"DISTORTION" indicated will be es­
sentially due to hum. When measuring
distortion with the low-pass filter, only
signals with a fundamental frequency
below approx. 80 Hz are relevant.
3. In the FLAT setting of the INPUT
FILTER switch, both filters are out
of action.
USING THE DISTORTION METER
WITHOUT THE BUILT-IN OSCILLATOR
1. Connect the output, for example, of an
AF generator to the INPUT of the
BKF10.
2. Check the input level (MAX. INPUT
switch setting).
3. Read off the distortion factor directly
on the Distortion Meter. No calibrat­
ing or balancing is necessary.
The INPUT FREQUENCY meter will
indicate the fundamental frequency.
The INPUT/OUTPUT Ri\TlO meter can
be used to indicate the signal level
in dB relative to the setting of the
LEVEL CONTROL switch (16) and the
VERNIER (15), provided the LEVEL AT
switch is set to OUTPUT.
The SIN function is not in use under
these conditions.
If it is desired to .sweep the AF gener­
ator, do so at a constant rate (per
decade). The sweep rate should not
exceed 1 decade per 20 seconds for
full resolution.
USING THE BUILT-IN OSCILLATOR
OUTPUT WITHOUT THE DISTORTION
METER
The BKF10 Oscillator with its extremely
low distortion «0.01%) may be used sep­
arately as an AF signal source.
1. Set LEVEL A switch (17) to OUTPUT.
2. Use LEVEL CONTROL (16) (and VER­
NIER (15), if necessary) to obtain the
output level required.
3. Set oscillator function switoh
(8)
to
either SINGLE SWEEP, MAN. or EXT.,
as required.
4. To monitor the frequency (output level
above 10 mV only), use a BNC T-con­
nector and connect the OUTPUT to
the INPUT with a short length of
screened cable. See Fig.
4.
SCREENED CABLE
F ig.
4.
OUTPUT