Yaesu FTDX-9000D, Руководство по эксплуатации

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Page 65 FT
DX
9000D O
PERATION
M
ANUAL
µ-Tune
Inspection of the illustrations to the right will demonstrate
the profound advantage of the µ-Tune circuit. In illustration
[
A
]
, the gray area represents the passband of a typical fixed
bandpass filter covering the 1.8 ~ 3 MHz range; this is typi-
cal of the kind of bandpass filter found in many high-quality
HF receivers today. Note also the hypothetical distribution
of signals across the 160-meter band.
In illustration
[
B
]
, note the narrow white segment within the
gray passband of the fixed BPF. These narrow segments rep-
resents the typical bandwidth of the µ-Tune filter, and one
can see that the passband has been reduced from about 750
kHz 9in the case of the fixed BPF) to a few dozen kHz when
µ-Tune is engaged. The vast majority of the incoming signals
are outside the passband of the high-Q µ-Tune filter, and they
will not impinge on any of the RF/IF amplifiers, the mixers,
or the DSP. Very strong out-of-band signals like this can cause
Intermodulation, blocking, and an elevated noise floor for a
receiver.
VRF
In this example, illustration [a] depicts a typical fixed bandpass
filter covering 14.5 to 22 MHz, and once again the gray shaded
area depicts the fixed bandpass filter’s frequency coverage.
The vertical lines in the illustration, once again, represent
hypothetical signals throughout this frequency range.
Figure [b] shows the same fixed BPF, with the white area
representing the typical passband of the VRF filter operating
in the same frequency range. Although the selectivity of the
VRF is not as tight as that of the µ-Tune filter, the RF selec-
tivity of the VRF preselector is still magnitudes better than
that of the usual fixed bandpass filter, affording significant
protection against the ingress of high signal voltage from
strong out-of-band signals.
U
SING THE
µ-T
UNE
F
EATURE
Advice
With µ-Tuning, the center frequency of the filter is continuously ad-
justable throughout its operating range, and the quality L/C compo-
nents ensure a tight passband due to the high Q of the circuit. The RF
preselection design task involves not only the selection of quality L/
C components, but the crafting of a tuning mechanism and tuning
concept that preserves system Q (thus assuring a tight bandwidth)
while providing a wide operating frequency range and consistent,
automated tuning. The smooth tuning is achieved by varying the in-
ductance over a wide range; this is accomplished by motor-driving a
large 1.1” (28 mm) ferrite core stack through a 2” high (50 mm) coil
structure. Three µ-Tune modules provide coverage of the 1.8, 80/40,
and 30/20 meter bands on the FT
DX
9000D, and the Q of this circuit,
being over 300, yields unmatched RF selectivity for outstanding re-
jection of undesired signals.
µ-Tune and VRF: Comparisons to Fixed Bandpass Filters
A
B
a
b
A
DVANCED
I
NTERFERENCE
-S
UPPRESSION
F
EATURES
: RF F
RONT
E
ND
1
2
3
4
VRF
µ -T
VRF
50-60 MHz
13.5-14.5 MHz
14.5-22 MHz
6.5-7.5 MHz
1.8-2.5 MHz
22-30 MHz
10-11 MHz
3.5-4 MHz
50-60 MHz
13.5-14.5 MHz
14.5-22 MHz
6.5-7.5 MHz
1.8-2.5 MHz
22-30 MHz
10-11 MHz
3.5-4 MHz
VFO-A
VFO-B
ANTENNA
AN
TEN
N
A SEL
EC
TO
R
BPF
14.5MHz 22MHz VRF BAND WIDTH
1.8MHz 2.5MHz
μ
TUNE BAND WIDTH
1.8MHz 2.5MHz
FRONT-END BAND WIDTH
14.5MHz 22MHz
FRONT-END BAND WIDTH