Bedienungsanleitung Yaesu FT-DX9000MP (Seite 153 von 164) (Englisch)

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Page 151FT DX 9000MP OPERATION MANUAL

RF µ-TUNING UNITS

(

MTU-160, MTU-80/40, MTU-30/20

)

µ-Tune

Inspection of the illustrations to the right will demon-

strate 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 typical of the kind of bandpass fil-

ter 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 seg-

ments represents the typical bandwidth of the µ-Tune

filter, and one can see that the passband has been re-

duced from about 750 kHz in 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 pass-

band of the high-Q µ-Tune filter, and they will not im-

pinge 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 fil-

ter 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 selectivity 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.

Advice

With µ-Tuning, the center frequency of the filter is continuously

adjustable throughout its operating range, and the quality L/C com-

ponents 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 mecha-

nism 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 inductance 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 160, 80/40, and 30/20 meter bands on the FT DX

9000MP, and the Q of this circuit, being over 300, yields un-

matched RF selectivity for outstanding rejection of undesired sig-

nals.

14.5MHz 22MHz

FRONT-END BAND WIDTH

14.5MHz 22MHzVRF BAND WIDTH

1.8MHz 2.5MHz

TUNE BAND WIDTH

1.8MHz 2.5MHz

FRONT-END BAND WIDTH

µ-Tune and VRF: Comparisons to Fixed Bandpass Filters

VRF

-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

ANTENNA SELECTOR

BPF

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