Kenwood TS-590SG Manual page 10

01 RECEPTION
The receiver mixer circuit is a quad mixer consisting of four 2SK1740 JFETs. The mixer circuit achieves superior
characteristics thanks to the revision of I/O port matching and the optimization of biases. With the signal provided by the
first local oscillator, the RX signal is converted to 11.374 MHz (first IF frequency).
The converted RX signal is moderately amplified at the post amplifier that compensates for the mixer loss, and sent to the
roofing filter when NB is OFF. When NB is ON, a 6 kHz NB band limiting filter is inserted before the post amplifier for the
band pass. The NB filter is inserted at this position to prevent the delay time from changing due to the target signal and noise.
The roofing filter is mounted with two 6-pole MCFs of 500 Hz and of 2.7 kHz as standard at the time of purchase of your
transceiver. Which filter is used is automatically determined according to the final pass bandwidth, i.e. depending on the
conditions including the bandwidth selection made with WIDTH or LO CUT/ HI CUT controls on the front panel.
For example, in CW or FSK mode, if WIDTH is 500 Hz or less, the 500 Hz filter is selected and if WIDTH is 600 Hz or more,
2.7 kHz filter is selected. In SSB mode, if the difference between the HI CUT and LO CUT frequencies is 2.7 kHz or less,
the 2.7 kHz filter is selected and if the combination produces exceeds a difference of 2.7 kHz, the up-conversion path is
automatically applied. (In SSB-DATA mode, if WIDTH is 500 Hz or less, the 500 Hz filter is selected.)
In AM and FM modes, because the pass bandwidth of the down conversion path is too narrow, the signal is received with
the up-conversion path.
These operations are used in the amateur radio bands of 1.8 MHz, 3.5 MHz, 7 MHz, 14 MHz and 21 MHz, and for other
amateur radio bands including WRC bands, and for other frequency ranges of general coverage receiving, up-conversion
is used regardless of the mode and pass bandwidth. (Since this switchover is determined by the CPU taking various
conditions into its criteria, the conversion path cannot manually be selected.)
Figure 1-4 is an image of the MCFs. From left to right, there is the 500 Hz filter at 11.374 MHz that is used in down conversion
and next is the 2.7 kHz filter at 11.374 MHz.
At the rightmost filter is the 2.7 kHz filter at 10.695 MHz that is used during the up-conversion.
6
Figure 1-4 MCF