03 Reception; Receiver Configuration; Conversion Method; Main Band Receiver - Kenwood TS-990S In-Depth Manual

03 RECEPTION

Receiver Configuration

The TS‑990S has two receivers; the main band receiver and the sub band receiver. This configuration enables dual
band reception using the main band and the sub band even if two bands are in the same band or different bands. During
transmission, the reception stops using both receivers. The bandscope circuit can select signals from either the main
band receiver or the sub band receiver, regardless of the selected band, and show the status of IF signals selected and
being transmitted (excluding FM modulated signals).

Conversion Method

Main Band Receiver

It is important for a receiver to eliminate interfering signals through narrow filters at an earlier stage and pass desired signals
to the subsequent circuits. Using filters with better selection characteristics for earlier elimination of interfering signals serves
to prevent distortion in the subsequent circuits and improves practical anti‑interference characteristics. The first mixer, through
which a number of interfering signals pass, needs to have high intercept point (referred to as IP hereafter) characteristics.
In developing the TS‑990S main band receiver, implementation of roofing filters with excellent selection characteristics and
high IP characteristics was the top‑priority. For the roofing filter implementation, the full down‑conversion method of the first
IF frequency of 8.248 MHz is adopted (the "down‑conversion" method used in the system is not intended for a conventional
configuration in which a high first IF frequency, e.g., the 73 MHz band is used but for a configuration in which a low first IF
frequency, e.g., 8 MHz band or 11 MHz band, is used). The use of a low IF frequency allows filters with steep attenuation
characteristics to be employed and performance sufficiently tolerant to adjacent interfering signals to be secured.
The next issue was the bandpass filters placed in the front‑end block of the main band receiver. The use of a low first IF frequency
allows interference on image frequencies and/or spurious reception to easily take place, thus it is necessary to place a number of
bandpass filters with steeper attenuation characteristics. As shown in the table "Bandpass Filter Division in the Main Band Filter",
bandpass filters for 15 paths are used, and for the major amateur bands (1.8 MHz, 3.5 MHz, 7 MHz, 14 MHz, and 21 MHz), a toroidal
coil with steep attenuation characteristics and high IP characteristics is used. Also, the bandpass filters for amateur bands including
other WARC bands are designed for positive use of parts with high Q (quality factor) and distortion resistance characteristics.
To eliminate distortion‑causing elements placed on the signaling paths in the front‑end block of the main band receiver, a
switching method through relays is used to select the bandpass filter, pre‑selector, pre‑amplifier, post‑amplifier, and roofing filter
for the major amateur bands. This also helps to reduce insertion loss and improve the isolation between the signaling paths.
Table 1 Bandpass Filter Division in the Main Band Receiver
Band
LF
BC
1.8 MHz
3.5 MHz
5 MHz
7 MHz
10 MHz
14 MHz
18 MHz
21 MHz
24 MHz
28 MHz
35 MHz
40 MHz
50 MHz
Filter Bandwidth
30 to 522 kHz
522 kHz to 1.705 MHz
1.705 to 2.5 MHz
2.5 to 4.1 MHz
4.1 to 6.0 MHz
6.0 to 7.5 MHz
7.5 to 10.5 MHz
10.5 to 14.5 MHz
14.5 to 18.5 MHz
18.5 to 21.5 MHz
21.5 to 26.5 MHz
26.5 to 35 MHz
35 to 40 MHz
40 to 46.5 MHz
46.5 to 60 MHz
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