Kenwood TS-870S (1996–2004)
A 100-watt all-mode HF transceiver whose fully digital IF signal path made DSP a working tool rather than a bullet point.
Overview
The TS-870S is Kenwood's "Intelligent Digital Enhanced Communications System." It's an all-mode HF transceiver that runs its signal path digitally at the IF stage on both transmit and receive. Plenty of radios from the period carried a DSP label bolted onto an otherwise analog chain. Kenwood's own documentation describes the TS-870S as having a fully digital signal path, with the adaptive filtering actually working on the signal before it reaches the operator's ears.
The architecture is a quadruple conversion superheterodyne, per the manufacturer's instruction manual, with intermediate frequencies at 73.05 MHz, 8.83 MHz, 455 kHz, and 11.3 kHz. Receiver coverage runs from 100 kHz to 30 MHz, so it's general coverage and not just the ham bands. Transmit operates across the 160 through 10-meter amateur bands. Output is rated at 100 watts in SSB, CW, FSK, and FM, dropping to 25 watts on AM. That AM figure is honest about what the finals can deliver in a 100% duty-cycle mode, and 25 watts of carrier is plenty for local AM work.
The radio takes DC 13.8 V at up to 20.5 A on transmit and around 2 A on receive with no signal. That makes it a shack radio, not a field rig. Antenna impedance is 50 ohms, and with the built-in tuner engaged the acceptable range widens to roughly 20-150 ohms, which covers most real-world wire and vertical installations without an external matchbox.
Key Features
Digital Signal Processing at the IF Stage
The TS-870S applies DSP on both transmit and receive, and the feature set that flows from it is where the radio earns its keep. Auto Notch, Beat Cancel, and Noise Reducer are the headline tools. They let an operator pull a weak signal out of a pileup without riding a manual notch control for ten minutes. The manual also lists Line Enhance among the adaptive filter functions, and notes that the same DSP works across SSB, CW, FM, and other modes rather than being locked to one.
On transmit, the DSP enables a Transmit Equalizer with high boost, bass boost, and comb filter functions. It's useful for anyone chasing audio punch on SSB, and it comes straight from the digital chain. You can't build that kind of flexible EQ into an analog mic amplifier without significant cost and complexity.
Advanced Intercept Point (AIP)
Kenwood's AIP function extends the receiver's dynamic range and reduces adjacent-signal interference. On a crowded band during a contest weekend, that's the difference between hearing the station you want and hearing the station 2 kHz away at the same strength. The manual groups AIP alongside IF Shift and the Noise Blanker as the receiver's interference-fighting tools.
Built-in Antenna Tuner
The TS-870S includes an automatic antenna tuner that can be switched into or out of the transmit and receive paths. Being able to bypass it counts, since a tuner in the receive path always costs a little sensitivity. If you're running a well-matched resonant antenna, you can take it out of the circuit. When engaged, it handles the 20-150 ohm range noted in the manual.
K-1 Logikey Electronic Keyer
The built-in keyer is a full-featured K-1 Logikey, and the manual is unusually candid about why it gets so many pages: not because it is hard to use, but because it has an incredible number of features. It has iambic operation with dot and dash memories, programmable commands sent from the key itself, and emulation modes for other keyer types. Soft-sectored messages can call each other with embedded functions. There's automatic contest serial number generation, and digital plus linear speed control from 6 to 60 wpm. Adjustable code element weight runs from 25% to 75%, and there is a tune function for continuous key down.
The default state out of the box is 20 wpm, 50% weight, auto-space off, character load mode, input queue on, serial number 001. The emulation default is K-1 Logikey, and function speed equals paddle speed. Kenwood's advice in the manual is to learn the basic functions first, then build up knowledge bit by bit rather than trying to memorize everything at once.
Computer Control Interface
A built-in RS-232C port allows direct computer control of the transceiver, with a user-selectable transfer rate between 1200 and 57600 bps. The command set includes both set and read commands. The manual gives the example of sending "FA00007000000;" to set VFO A to 7 MHz, or "FA;" to read it back. Anyone writing their own control software or building a logging and automation setup will find that documentation useful.
The radio stores 100 memory channels, and supported modes per the manual's command reference are J3E (LSB, USB), A1A (CW), A3E (AM), F3E (FM), and F1D (FSK).
Antenna Switching and Connections
The rear panel provides ANTENNA 1 and ANTENNA 2 connections, along with a PADDLE jack and a KEY jack for connecting a paddle, an external keyer, or a keyboard. The supplied accessories include a DC power cable, a microphone, and fuses rated at 25 A and 4 A.
Historical Context
The TS-870S was produced between 1996 and 2004, according to the available documentation, and Kenwood positioned it as the replacement for the TS-850S and TS-850SAT. The radio is now out of production. It arrived when DSP was moving from a premium curiosity to a core part of receiver design, and Kenwood built the entire IF chain around it rather than treating it as an add-on.
The manual's introduction frames the design as the work of engineers "determined to continue the tradition of excellence and innovation in KENWOOD HF transceivers," and the feature list backs that up: Auto Notch, Beat Cancel, and Noise Reducer as operating tools, paired with IF Shift, Noise Blanker, and AIP for interference fighting. Kenwood's own copy describes the radio as setting new standards in its class. That's marketing, and should be read as such, but the underlying architecture was forward-looking for 1996.
Collectibility & Value
The TS-870S carried an MSRP of 2399.00 at launch. On the second-hand market, examples have traded around £999.00 for a boxed TS-870SAT with original manual and mic, and one 2008 listing showed a good-condition TS-870SAT at USD 1129.95. Those are old data points, and current values will vary with condition and included accessories. A complete package with the original hand mic, power cord, and manual commands more than a bare radio.
Kenwood paired the TS-870S with specific accessories that turn up in listings: the PS430 power supply with OEM cable and the SP930 speaker with auto filtering. A complete station of radio, supply, speaker, mic, and manual is the configuration collectors look for, and one classified listing described exactly that setup as being in excellent condition.
A known troubleshooting topic is low transmit power, which appears in the documentation as a commonly encountered operational issue rather than a circuit failure. The manual's troubleshooting section is explicit that many reported problems trace to improper hook-up, incorrect control settings, or operator error. Check those before assuming the finals are gone. Two quirks are documented in the manual: beat tones may be heard at 10.000 MHz, 20.000 MHz, and 30.000 MHz due to frequency relationships within the circuits, and placing a powered handy transceiver near the TS-870S can introduce noise. Neither is a fault.
Service documentation exists in the form of a user manual hosted on QRZ.RU, and schematics for the TS-870S variant are also in circulation. The menu system and keyer programming alone are reason enough to keep the documentation on hand.
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