Transmission; Kenwood Traditional Transmitting Circuitry; If Circuits; Alc Circuit - Kenwood TS-590SG Manual

02 TRANSMISSION

2.1 KENWOOD Traditional Transmitting Circuitry

The tradition of high quality audio technology that users rely on KENWOOD to deliver is produced by combining analog
and digital technologies that KENWOOD has nurtured thus far. The DSP controls modulation and determines the sound
quality and analog circuits convey and amplify the signal cleanly.

2.1.1 IF Circuits

The first IF transmit signal that is processed by the DSP and output at 24 kHz from the DA converter is converted to 10.695
MHz in a dedicated IC for the mixer. The second IF signal at 10.695 MHz passes an IF filter of 6 kHz bandwidth at which
undesired frequency components outside the pass bandwidth are attenuated before the signal is amplified. Next, the signal
goes through the gain control circuit that corrects the differences in gain from band to band, and the signal enters the mixer
that is commonly used in TX and RX, and is converted to the third IF of 73.095 MHz. The signal passes through the gain
control circuit that adjusts the signal to the necessary gain level to output the specified power level. After the signal passes
the filter that eliminates spurious components, the power is controlled by an ALC circuit to prevent it from exceeding a certain
level before the signal enters the mixer circuit that converts it to the desired transmit frequency. Also, delicate control is
done, such as stopping the operation of the amplifier while the key is not depressed in CW mode. The signal converted
to the desired transmit frequency passes the BPF for removing spurious signals to prevent from generating interference
outside the transmit bandwidth, and is amplified to a prescribed level before being sent to the final circuit. The drive signal
produced here can be extracted from the DRV terminal. (While the output from DRV is selected.)
In the SSB mode, control is performed by the ALC circuit for the peak envelope power to reach the predetermined setting.
To prevent distortion of the wave to be transmitted when there is a large input, the output level is restricted through DSP by
a AGC upon exceeding a certain level. This prevents any distortion from occurring in the analog circuit after IF. It helps to
prevent distortion as well as splatter from occurring even in the event of a loud sound level. With such meticulous attention
paid to control the level, a high-quality transmit signal with low noise can be acquired.

2.1.2 ALC Circuit

Adopting an ALC control system developed for use on the TS-990S, the TS-590SG is able to send out properly-controlled
signals even at the initial rise of the SSB transmission signal.

2.1.3 FET Final Circuit

The final amplifier is a push-pull amplifier using two pieces of RD100HHF1 MOSFET from Mitsubishi Electric Semiconductor
(Pch 176.5 W). The drive amplifier uses an RD16HHF1 MOSFET and the pre-drive amplifier uses an RD06HHF1 MOSFET,
despite being 13.8 V final circuits, the amplifiers are able to amplify the signal reasonably in a stable and continuous manner
with low distortion. Figure 2-1 shows the graph of IMD characteristics and Figure 2-2 shows the graph of harmonic spurious
characteristics. Superior distortion characteristics and clean signals are acquired in this way.
13