38
FT-847 O
PERATING
M
ANUAL
DSP N
OISE
R
EDUCTION
The Digital Signal Processing (DSP) circuitry includes
a highly-effective N
OISE
R
EDUCTION
feature, which may
be used alone or in conjunction with the IF N
OISE
B
LANKER
. The DSP N
OISE
R
EDUCTION
circuit can be ef-
fective against a wide variety of noise types; it is not
limited to the “impulse” noise such as ignition noise.
However, because the N
OISE
R
EDUCTION
is effected in
the audio stage, the operator may have to work around
the effects of the AGC circuitry. Here’s how to use the
DSP N
OISE
R
EDUCTION
feature:
•
To turn the N
OISE
R
EDUCTION
feature on,
press the [
NR
] switch. The “
NR
” icon
will appear on the display. You should
notice a significant reduction in the back-
ground noise.
‚
If the noise is strong enough to be mov-
ing the S-Meter (thereby indicating that AGC volt-
age is being produced by the strong noise level),
you may find the DSP N
OISE
R
EDUCTION
to be more
effective if you take one of the following steps:
l
Switch off the RF P
REAMPLIFIER
;
l
Engage the RF A
TTENUATOR
; or
l
Rotate the
RF
(G
AIN
) control counter-clockwise
until the S-meter reading “hangs” at the peak S-
Meter reading on the noise.
ƒ
The level of noise reduction applied by the DSP
may be adjusted via Menu #11. The default set-
ting, on an arbitrary scale of
0
(minimum noise
reduction) to
15
(maximum noise reduction) is
7
.
A higher setting will provide more noise quieting,
with slightly degraded fidelity; a setting lower than
7
will improve received signal quality, but with
slightly less-effective noise reduction.
„
To turn the DSP N
OISE
R
EDUCTION
feature off, press
the [
NR
] switch again. The “
NR
” icon will disap-
pear from the display.
OPERATION
R
ECEIVER
F
EATURES
S
QUELCH
(R
ECEIVER
M
UTING
)
The S
QUELCH
circuit allows muting of the receiver’s
audio circuits during operating sessions where you
wish to quiet the receiver except when a signal is
present.
To set the proper sensitivity thresh-
old for the S
QUELCH
circuit, rotate the
SQL
control clockwise until the
background noise just disappears.
This threshold point provides the best
sensitivity to weak signals, while en-
suring proper quieting during quiescent periods.
When a signal is received which exceeds the thresh-
old set by the
SQL
control, the muting function will
be disabled and normal receiver audio will flow. When
the signal disappears, the receiver will again be muted.
To disable the S
QUELCH
system’s muting action, rotate
the
SQL
control fully counter-clockwise.
The S
QUELCH
circuitry is most often used during FM
operation, but the FT-847’s S
QUELCH
system is opera-
tional in all modes. There are additional muting func-
tions associated with FM operation (CTCSS and DCS),
and these are described on page 53.
V
OICE
S
YNTHESIZER
The FT-847 includes the capability for the use
of the (optional)
FVS-1A
V
OICE
S
YNTHESIZER
,
which provides an audible announcement of
the current operating frequency (receive fre-
quency).
To confirm the current frequency, press the [
VOICE
]
key, located between the
MAIN VFO
Tuning Dial and
the
AF
/
RF
(G
AIN
) controls. Frequency resolution to
the displayed 100 Hz digit is provided. For example,
if the frequency is 145.910.0 MHz, the
FVS-1A
will
announce: “
One-Four-Five-Point-Nine-One-Zero-Zero
.”
Note
: The V
OICE
S
YNTHESIZER
announces the receive fre-
quency; in “Split” operation, the receive fre-
quency is displayed on the S
UB
VFO frequency
display field.
