Kenwood TS-680S Instruction Manual

Also see for TS-140S: Instruction manual Instruction manual Instruction manual Instruction manual Instruction manual

5. CIRCUIT DESCRIPTION5-1. GENERAL DESCRIPTIONThe TS-140S/680S utilizes double-conversion forFM transmissions, and triple-conversion for all othertransmission modes, and for all modes in receive.The intermediate frequencies are 40.055 MHz and455 kHz.A wide dynamic range is made possible thru the useof 2SK125 junction FET’s in the receiver section’s1st and 2nd mixers.An integrated circuit balanced modulator(SN16913) is used in the 1st transmitter mixer and3SK122 is used in the 2nd mixer. The PLL circuit,consisting of 4 loops, and the digital VFO are con-trolled by a single reference oscillator circuit. IFSHIFT and 10 Hz tuning steps are provided thru theuse of this system.5-2. TRANSMITTER SECTIONThe incoming microphone audio is routed to the SWunit where it is amplified by the microphone amplifierand then distributed to the SSB, FM and VOX cir-cuits. (VOX circuit is TS-140S only.)The amplified SSB audio signals are canverted inta a455 kHz DSB (Double Sideband) signal by thebalanced modulator {AN612). The signal is thenfiltered by a ceramic filter in order to abtain thedesired SSB signal. This signal is then mixed with alocal ascillator signal of 39.6 MHz by the first mixerwhich results in a 40.055 MHz signal. This signal isfiltered by a monolithic crystal filter (MCF) and com-bined with the VCO frequency, in the 2nd Mixer, toobtain the final transmit frequency. In FM themicrophone audio signal is amplified and used todirectly modulate the 39.6 MHz local gscillator. ThisFM signal is then mixed with the VCO signal to ob-tain the final transmit frequency. The SSB and FMsignals enter the final unit for amplification to thefinal output power level. This signal is applied to theLow Pass Filter where unwanted spurigus com-ponents are removed before actual transmission.5-3. RECEIVER SECTIONThe incoming signal for the antenna is fed to thereceive band-pass filters in the signal unit, via a frontpanel controlled attenuator circuit.The appropriate bandpass filter is automaticallyselected based upon control information supplied bythe Control Unit. Independent RF amplifiers are alsoincluded for the 28, and 50 MHz bands and can beturned OFF or ON via a front panel control. (TS-680Sonly)Signals from the BPF are mixed with the VCO signalin the 1st RX mixer to obtain the 1st IF frequency of40.055 MHz. This signal is filtered by a MCF(Monolithic Crystal Filter) and applied to the 2nd RXmixer. This mixer combines the 1st IF frequencywith the HET OSC frequency of 39.6 MHz to obtainthe 2nd IF frequency of 455 kHz.28This signal is separated and applied to two differentareas. One is used to control the operation of theNoise Blanker. The other signal passes the NoiseBlanker gate is amplified, and passed thru the ap-propriate IF filter. The SSB, CW, and AM signals areamplified further and then demodulated by theirrespective detector circuits. The FM_ signal isamplified and detected in a custom IC.5-4. CIRCUIT BOARD DESCRIPTIONThe 1S-140S/680S contains the following majorunits: Signal unit, Control unit, Filter unit, Final unit,Display unit, Switch unit, etc. A brief description ofthese units follows.5-4-1. Signal Unit (X57-3190-00, 3200-10)The signal unit is composed of the transmit andreceive sections. These consists of the Signalsystem amplifiers, mixers, detectors, modulators,filters, VCO’s, and the various timing circuits usedfor transmit/receive switching. This unit handlespractically all TS-140S/680S signal processing.§-4-2. Control Unit (X53-3100-11, 12)The control unit is composed of the frequency con-trol section which is controlled by a microprocessorand four PLL loops. The unit also contains areference oscillator, operating at 36 MHz, which isthe reference for all frequencies generated by thetransceiver,5-4-3. Display Unit (X54-3050-00}The display unit consists of a fluorescent displaytub, LED indicator section, DC to DC converter, andvarious switching circuits.5-4-4. Final Unit (X45-3100-00, 11)This unit amplifies the TX RF signal for transmission.This is accomplished by utilizing a three-stage finalamplifier section having a relatively low collectorloss figure, and a high efficiency cooling system.5-4-5. Fitter Unit (X51-3040-00, 11}The filter unit removes the undesirable spurious highfrequency components from the transmitter output.4 50 MHz power module is also included in this sec-tion for the TS-680S.5-4-6. Switch Unit (X41-3030-00, 11)The switch unit includes the speech processor andthe MIC amp circuit.