Manual FCKL 1528 Page 9
4.5.4 Rotary switch
to select manual or automatic tuning and xy-recorder positioning. In the Man position
the receiver's frequency is tuned by the encoder. In the Start position a clock generator
does this tuning work.
The scanning procedure always begins at 9 kHz or at the
frequecy tuned with Man and is only possible for rising frequency.
The 2 edge positions
set the frequency to 9 kHz or 29.999 MHz respectively. This makes life easier when
adjusting the xy recorder to a diagram.
4.6 AF/AUDIO
This area contains both a. f.-volume control
(6.1)
and demodulator switch
(6.2).
The
a. f.-volume control works just like in a radio receiver, but it has to be considered, that
especially in band A the loudness sometimes is poor. The reason is that the very
narrow bandwidth of 200 Hz can only deliver very low a.f. frequencies to the
loudspeaker which is too small for this purpose. Often the operator compensates for
this low volume by increasing a.f. amplification with the volume control. This results in
overloading and by that harmonic distortion is produced. This harmonic distortion then
gives higher volume. In the norm position of the demodulation switch input signals are
demodulated as if they were amplitude modulated, which is the case for most of the
signals in this frequency range, especially broadcast stations. Pulse noise and
calibration signal can be monitored well in this position. The positions BFO 0k and BFO
1k are useful if unmodulated narrow band signals occur. Being unmodulated, there is
no information to listen to. Only some variation in basic noise can be monitored. If a
BFO is in use, the differential frequency between input signal and receiving frequency
occurs. This differential frequency is exactly the difference between these two
frequencies if the switch is in the 0 k position. If the difference is 0 (zero beat) both
frequencies are equal. For the narrow bandwidth of band A an audible difference
frequency cannot appear. The problem is solved by using BFO 1k position. Both
frequencies are equal if a 1 kHz difference frequency is heard. Due to the more and
more automatic measurements these considerations seem to be less important. But it
is still very important especially when working without shielding room to verify a signal
to know if it is interference or broadcast. Also the acoustic signature of a signal gives
some information.
4.7 Selecting detectors, QP, PK, AV, CAV, CRMS
Select detectors according to the standard.
Continuous sine wave signals give the same reading on all detectors.
Changing signals and pulses give different readings.
4.7.1 CISPR Quasi-Peak QP
This detector has a pulse weighing characteristic which considers the annoyance.
If single clicks or slow pulses are to be measured, choose lin y / low distortion of
switch 4. Highest precision is obtained, if both attenuators (2.2) and (2.3) are used to
adjust the signal to the 0 dB marker of the linear (lower) scale. The precision is then
better than required. The measurement reading can be done in the display (2.1) for 0
dB (centre) meter reading.
4.7.2 Peak PK
Centre position of switch (7) gives reading of the unvalued peak voltage.
The Peak Detector has an extremely short charge time constant and is self-resetting.
The measurement is the peak value, related to the bandwidth, based on the calibration
of the effective value of a sine wave.