Pre-Selector - Kenwood TS-990S In-Depth Manual

03 reception

Pre-selector

The pre-selector is implemented to attenuate, by using a narrowband filter, the in-band interfering signals that cannot be eliminated
by the bandpass filters in the front-end block of the main band receiver and to elicit the desired signals. The "Pre-Selector Unitary
Resonance Circuit" shows its internal resonance circuit. A method of relay-switching of highly accurate capacitors, toroidal coils,
etc. enables it to change the precisely tuned frequency in accordance with the received frequency in the HF amateur bands. The
"Available Band and Step Frequency Specifications" table shows the available bands and step frequencies.
Band
1.8 MHz
3.5 MHz
5 MHz
7 MHz
10 MHz
14 MHz
18 MHz
21 MHz
24 MHz
28 MHz
The frequency response shape a steep single-peaked pattern. A large-sized coil with less loss is used; however, a large
insertion loss may be inevitable; therefore, an amplifier is placed after the pre-selector to compensate the loss. Signal
level correction in connection with the amplifier is also applied to suppress deflection of the S meter needle. To prevent
the reception noise level from rising, it is designed so that the pre-amplifiers do not work in conjunction with it. Thus,
enabling the pre-selector disables the pre-amplifiers.
8
Fig. 9 Photograph of the Roofing Filter in the Sub Band Receiver
Fig. 10 Pre-Selector Unitary Resonance Circuit
Table 3 Available Band and Step Frequency Specifications
Range
1.79750 to 2.00499 MHz
3.49250 to 4.01749 MHz
5.24000 to 5.46999 MHz
6.98000 to 7.33999 MHz
9.98000 to 10.17999 MHz
13.95000 to 14.44999 MHz
18.01800 to 18.26799 MHz
20.90000 to 21.69999 MHz
24.79000 to 25.18999 MHz
27.90000 to 29.89999 MHz
Step Frequency
2.5 kHz
7.5 kHz
10.0 kHz
20.0 kHz
20.0 kHz
50.0 kHz
50.0 kHz
100.0 kHz
100.0 kHz
100.0 kHz
3 dB Passband
Width
20 kHz
50 kHz
100 kHz
120 kHz
220 kHz
620 kHz
880 kHz
880 kHz
1120 kHz
1170 kHz