Receiver Operation (Front End Block Diagram) - Yaesu FT-2000 Operating Manual

C
ONVENIENCE
R
ECEIVER
The FT-2000D includes a wide range of special features to suppress the many types of interference that may be encoun-
tered on the HF bands. However, real world interference conditions are constantly changing, so optimum setting of the
controls is somewhat of an art, requiring familiarity with the types of interference and the subtle effects of some of the
controls. Therefore, the following information is provided as a general guideline for typical situations, and a starting point
for your own experimentation.
The FT-2000D's interference-fighting circuitry begins in its "RF" stages, and continues throughout the entire receiver
section. FT-2000D allows configuration of the features described below. However, the Sub band (VFO-B) receiver does
not have the DSP (Digital Signal Processor) features.
VRF
S 53
On the 1.9 - 28 MHz Amateur bands, Yaesu's powerful
VRF (Variable RF Filter) preselector circuit provides ex-
cellent suppression of out-of-band interference, with a
passband much narrower than that provided by traditional
fixed bandpass filters.
R. FLT
IF Roofing Filters
On the Main (VFO-A) receiver, three automatically-se-
lected Roofing filters, in bandwidths of 15 kHz, 6 kHz,
and 3 kHz, are provided in the 69 MHz First IF, right after
the first mixer. These filters provide narrow-band selec-
tivity to protect the following IF and DSP stages, and the
filters' automatically-selected bandwidths may be manu-
ally changed by the operator, if desired, for special oper-
ating circumstances.
The Sub (VFO-B) receiver's 40 MHz IF includes a fixed
Roofing filter, with a bandwidth of 15 kHz.
CONTOUR Filter
S
The DSP Contour filter is a unique capability on the Main
(VFO-A) receiver, providing either nulling or peaking of
tunable segments of the receiver passband, so as to sup-
press interference or excessive frequency components on
an incoming signal, or to peak those tunable frequency
segments. The amount of nulling/peaking, and the band-
width over which it is applied, are adjustable via the Menu.
IF SHIFT
S 56
The passband center frequency response of the IF DSP
filtering may be adjusted using this control.
IF WIDTH
S 57
The width of the IF DSP filtering may be adjusted using
this control.
ATT
ANTENNA
SELECTOR
Page 50
F
EATURES
O
PERATION
S 54
55
RF
THRU
IPO OFF
OPTION
µ-TUNE
BPF RF AMP 1
VRF RF AMP 2
F E B
RONT ND LOCK
IF NOTCH
S
The IF Notch filter is a high-Q notch filter that can signifi-
cantly reduce, if not eliminate, an interfering carrier. The
Q (sharpness) of the filter may be adjusted using the Menu.
DNR
D N
The DSP's Digital Noise Reduction (DNR) feature uti-
lizes sixteen different mathematical algorithms to analyze
and suppress different noise profiles encountered on the
HF/50 MHz bands. Choose the selection that provides the
best noise suppression, which concurrently will allow the
signal to rise up out of the noise.
DNF
D N
When multiple interfering carriers are encountered during
reception, the Digital Notch Filter can significantly reduce
the level of these signals.
AGC
S 62
The AGC system is highly adaptable to changing signal
and fading characteristics, making reception possible un-
der the most difficult conditions.
SLOPED AGC
The Sloped AGC system on the Main (VFO-A) receiver,
instead of clamping a fixed upper bound on audio output
across a wide range of input signals, actually allows the
audio output to rise, very gently, with ever-increasing sig-
nal strength. This capability allows you to separate sig-
nals, using your brain, according to signal strength in ad-
dition to slight frequency differences.
IF Filter Quality Adjustment
The "Q" (quality factor) of the IF DSP filters may be ad-
justed using the Menu.
Variable IF Filter Shape Factor
You may adjust the shape factor of the receiver IF DSP
filters using the Menu.
1st IF
69.450 MHz
ROOFING
FILTER
1st
IF AMP
3k/6k/15k
1st Local 2nd Local
1st IF
40.455 MHz
ROOFING
FILTER
1st
IF AMP
15k
1st Local 2nd Local
FT-2000D O
D
IAGRAM
58
R S 59
S 59
S 63
S
S
( )
Main Band VFO-A
2nd IF 3rd IF ( DSP )
450 kHz 30 kHz
2nd DSP
CF
IF AMP UNIT
3rd Local
( )
Sub Band VFO-B
2nd IF
455 kHz
2nd
CF DET
IF AMP
M
125
125