Yaesu FTDX9000D - DATA MANAGEMENT Operation Manual page 68

A I
DVANCED NTERFERENCE
The μ-Tune filters are the most advanced, selective RF preselector filters ever incorporated into an Amateur
Radio transceiver. The RF selectivity provided by μ-Tune can be of tremendous value in ensuring quiet, intermod-
free reception even in the most crowded bands on a contest weekend. The μ-Tune filters provide RF selectivity
on the order of a few dozen kHz at –6 dB, at the expense of a few dB of system gain on bands where noise figure
is seldom an issue. You will notice that the S-meter deflection, when μ-Tune is engaged, is slightly less than
when it is out of the circuit; this is normal. If your antenna system gain is so low as to make it impossible to hear
band noise when μ-Tune is engaged (highly unlikely), just switch it out or revert to the VRF system, which has
slightly less insertion loss.
As you tune around on an amateur band with μ-Tune engaged, the microprocessor automatically commands the
stepper motor driving the toroid core stack to center the filter on your current operating frequency. You may,
however, use the [ VRF/µ-T ] knob to skew the filter response to one side or the other from your operating
frequency, to deal with heavy interference on one side. To re-center the μ-Tune filter on your operating fre-
quency, and eliminate any offset, press and hold in the [ VRF/µ-T ] switch for two seconds.
A pictorial representation of the tuning position of the μ-Tune filter will appear on the bar graph on the TFT.
While μ-Tune is a superior RF preselection circuit, it may be disabled via the Menu; if this is done, the VRF
circuit will engage when the [ VRF/µ-T ] switch is pressed. To disable μ-Tune, go to Menu item "GENERAL
043 μTUNE DIAL STEP" and set the selection to "OFF."
µ-Tune and VRF: Comparisons to Fixed Bandpass Filters
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.
[ ]
B
In illustration , 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 sig-
nals 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
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.
Page 66
-S
UPPRESSION
U µ-T
SING THE
A A A A A
D D D D D VICE
[ ]
a depicts a typical fixed
F : RF F
EATURES
F
UNE EATURE
VICE VICE VICE VICE
A
1.8MHz
FRONT-END BAND WIDTH
B
1.8MHz TUNE BAND WIDTH
μ
a
14.5MHz
FRONT-END BAND WIDTH
b
14.5MHz VRF BAND WIDTH
FT 9000D O
DX
E
RONT ND
2.5MHz
2.5MHz
22MHz
22MHz
M
PERATION ANUAL