Furuno FM-8800D Service Manual page 154

SQ/Auto SQ FUNCTION
SQ FUNCTIONS are below;
- Threshold level
- Tight level
CAUTION:
SQ auto function is the position of SQ volume at around 7 o'clock. Note that
dose not control audio spectrum as FM-8500 does.
SQ control is carried out in SQ Cont inside DSP shown in Fig. 5.4.17. SQ function is
based on a ratio between the level of audio range and the level of noise range. For
example, there will be no audio signal when the level of audio range and the level of
noise range are the same. Inputting audio signal will increase the level of audio range
and suppresses the level of noise range.
A ratio table (SINAD) of noise and signal is made beforehand and the level that controls
each detected level and the level with which they are controlled from the position of SQ
volume. You can check the level of noise range and the level of signal range by
selecting [MENU] -> SYSTEM -> TEST -> TX/RX STATUS and checking RX IF
LEVEL and RX AF NOISE. Refer to page 8-15.
Noise area
8kHz
25kHz
No signal
SQ Cont: Refer to Fig. 5.4.17.
SQ control is a MUTE circuit of FM DEMOD OUT (Voice) line. This signal is
outputted into the Handset era-speaker and SP of the Transceiver unit. FM DEMOD
(Voice) line is the output of Remote Handset's LINE OUT and VDR OUT, therefore, SQ
control is not carried out here.
SQ control for a Remote Handset
SQ level set up on the Remote Handsets side goes through DATA line and controls this
circuit: SQ Cont. A signal (SQ) that controls MUTE circuit is sent to the Remote
Handset side and controls the sound there.
: -3 to –6 dBuV (approximately SINAD 12 dB)
: below +6 dB
37.5kHz
50kHz
+12.5kHz
Signal area
When there is a signal, signal level increases and noise level
is suppressed. Noise range is within the level ranging from
8 kHz up to 25 kHz.
Fig. 5.4.18 Signal Range and Noise Range
;
5-22
5.4 Block Description
37.5kHz
Noise area
8kHz
25kHz
Signal area
50kHz
+12.5kHz