TS-870S review by K6YAZ

Kenwood TS-870S HF Transceiver

by Stuart Landau K6YAZ

We are promised that conditions on the high frequency amateur bands are going to be getting better with the startup of the next sunspot cycle. For now, the average ham, with a 100 watt station using antennas that are acceptable in an urban location, are having a difficult time working weaker stations through man-made and natural noise.

Certainly high power and large antennas will help, but many of us just can’t afford to go that route. Antenna restrictions and interference to consumer electronics creates a difficult situation that we have to Jive with, or give up that part of our hobby. We need an edge to make amateur radio as enjoyable as possible, and I for one don’t want to put off working the low bands until things improve, in a few years.

Kenwood has just released its newest and most advanced high frequency transceiver. The design feature that is unique in the amateur market (at least for now) is the use of a digital signal processor (DSP) that processes signals at the intermediate frequency (IF) as well as at audio frequencies. This has also been done recently by other companies making radios for the commercial and military markets (and their products may he purchased at great expense),

Kenwood was the first amateur radio company to design DSP into an amateur transceiver (in the TS-950 SD and SDX), and now they’ve expanded greatly beyond their original efforts, and they seem to have done it right! I’ve been able to copy signals on the TS-S70S, buried in so much noise that I couldn’t copy on other receivers, and that’s what its all about. You canTt work them if you can’t hear them.

Description of the radio:

Lets start with the receiver, since it is what you would spend your time listening to, not the transmitted signal. It is a quadruple conversion type superheterodyne. The frequencies used are 1st: 73*05 MHz; 2nd: 8,83 MHz; 3rd 455 kHz and 4th: 11.3 kHz. All filters are included in the radio. The IF filtering is mainly done by the DSP. In addition to the DSP IF filtering, the radio contains nine crystal or ceramic filters located in the first three of the four IF frequencies, to act as additional bandwidth limiters. These are automatically selected by mode and operator-selected, CW bandwidths range from I kHz down to 50 Hz in six steps. On FSK they range from 1,5 kHz to 250 Hz in four steps and on FM six different widths from 14 kHz to 5 kHz. On SSB, slope tuning may be used, resulting in twelve different widths ranging from 1.4 kHz up to 6.0 kHz* Six band-widths on AM complete the possibilities.

The reason that it is important to process the signal at IF instead of audio, is that once the signal has been detected, the DSP has lost a lot of the information that it requires to discriminate between noise and intelligence. For the most efficient transfer of voice or data, the receive filter must be matched to the transmitted signal, and predetection filtering is the optimum method, it makes little sense to have an overly wide bandwidth, and to attempt to make up for that by using a narrow audio filter. Certain artifacts will now ride along with the desired signal that make it very difficult to separate the desired signal from the noise.

A digital signal processor is a very specialized type of microprocessor. It crunches numbers, and in this case two DSP chips do it very quickly. In the receive mode, the analog signal is mixed down to a very low intermediate frequency of 11.3 kHz and converted into a digital stream of numbers, The DSP acts as IF filter, demodulator, AGC processor, squelch processor and—very importantly—as a noise processor. All of this occurs in a section of the radio which doesn’t have any service adjustments!

When transmitting, the modulation with the exception of FM, is generated by the DSP, which also serves as a microphone AGC amplifier, voice equalizer, speech processor, VOX controller and sidetone generator. Whew!, what a busy region of the radio. Suffice it to say that this is one complex system

The DSP section of this radio consists of two Motorola DSP56002FC240 132 pin, 24 bit chips with a claimed dynamic range of 144 dB. The IF to digital converter is an 18 bit sigma-delta (also known as a one bit) A/D converter. The IF is highly over-sampled, resulting in a very quiet digital signal with a very large dynamic range.

The DSP IF filtering creates filters that have shape factors, pass band flatness, very high out-of-pass band attenuation and phase characteristics that are impossible to build any other way,

The transmitted signals are generated in the DSP, and mixed up several times to the transmit frequency, and amplified by the final amplifier unit. The RF portion of the transmitter, for the most part, is very similar to that of the TS-850S.

The frequency synthesizer consists of three phase lock loops and three direct digital synthesizers, all controlled by a CPU. A 20 MHz crystal oscillator serves as the only reference oscillator in the radio. The result seems to be a very fast, quiet radio.

Using the radio:

My approach to writing the evaluation of the radio was to ask friends of mine to use the radio, and give me their opinions. I didn’t expect a consensus, but I ihink several opinions and observations are valuable.

While this radio is user friendly, it will require studying the instruction manual and practice to be abie to take full advantage of the radio’s unique features. It’s not a beginner s radio. It would be a waste of money to buy a piece of equipment such as this and not be able to take full advantage of what it has to offer,

The TS-870S comes with a built-in antenna tuner and doesn’t require (or will accept) any additional IF filters, all are already synthesized by the DSP. A sophisticated CW keyer is also included with the radio. It will operate from six to sixty words per minute, and emulates the K-l Logikey. A normal key or paddle is all that’s needed to get on CW. The radio will store four CW messages with a total of 220 characters. This sounds like a great feature for contesting. Options include a voice synthesizer, a digital recording system, and a high stability temperature-compensated crystal oscillator. An 8,83 MHz full bandwidth IF output is provided on the rear panel to be used with a station monitor such as the older Kenwood SM-220 or current SM-230.

DR Ulrich Rohde KA2WEH, well known for his communications books and articles in amateur publications was a consultant for Kenwood on the design of the receiver. His insistence that PIN diodes, rather than silicon PN switching diodes be used in critical spots in the receiver front end, has resulted in a receiver with great immunity to overload. He had the use of a pre-production radio this summer and the opportunity to make some sophisticated measurements. I use his results with his permission.

Phase Noise: -120 dBc/Hz at 10 kHz, -126 dBc/Hz at 20 kHz

This indicated a very quiet frequency synthesizer, resulting in a narrow transmitted noise signal, and low reciprocal mixing in the receiver.

Third Order Intercept Point: 22 dBm with AIP on.

Second Order Intercept Point: 64 dBm with AIP on.

This indicated the ability to reject interference when there are many strong signals inside and outside of the band.

Dynamic Range: 95.3 dB with AIP on, 91.6 dB with preamp on. Ulrich said to me that he considered the receiver in the TS-870S the best currently available at its price.

The display is similar to that cur rently used in the Kenwood models TS-950SDX and TS-450S. It is a good-looking mufti-colored display, carefully thought-out to help the operator. The only shortcoming of this type of display is that is very hard to see in bright sunlight. I’ve used both the TS-450S and the TS-870S in my car, and while most operators won’t use this radio mobile or outdoors, it’s something to consider.

Unlike ail other Kenwood High Frequency radios, the front feet don’t raise up. If you want the radio to Lilt up to face you, you’ll have to put something under the front or build a ramp. The main tuning knob now has a rubber cover around the outside and a depression on the front tor

your finger, but doesn’t have any adjustable friction adjustment. There are two tuning rates available on the main knob, and a much faster rate using the M.CH/ VFO.CH, control, I find the rate and feel to be very comfortable. Push-buttons either light up when they are in the on position, or light up an indicator on the display to indicate the state that they are in.

The instruction manual is very well-written and illustrated. The introduction and one page of the appendix explains something about the DSP and how it is used. Also included are sections on standard time stations, the NCDXF/IARU beacon network, HF beacons and the shortwave broadcast bands. The remainder of the appendix explains the digital interface for computer control (using RS-232C).

Computer Control Of The TS-870s:

The TS-870S includes a built-in RS-232C port and comes with two 3,5 inch floppy disks, containing a DOS- or Windows-compatible software program called Radio Control Program™. RCP will allow complete control of the radio via a personal computer. It will let you use or create a virtual radio” on your screen. As long as you can provide a two way communications path at baud rates of from 1200 to 57600 bps, and audio lines, you can completely control the radio, and locate it anywhere! Optional software modules are available from DynaNet Corporation, The S70S can also transfer data (receive frequency and receive mode) to another 870S or four other types of Kenwood transceivers.

The microphone supplied with the ra dio is the MC-43S hand mic, the same that has been used for many years. This microphone provides up and down buttons for changing frequency or memories, but no “soft keys” as on the TS-50S and TS-60S microphone, I would suspect that most buyers will opt for some sort of desk mic.

The TS-870S is a descendent of the TS 850S, The dimensions are exactly the same and at 25 pounds weighs only one pound more. Someone comfortable with the operations of the 850 would feel at home using the 870,

At a list price of $3199, and considering the typical dealer discounts, the selling price shouldn’t be much more than the TS-850S, especially if you loaded up the 850 with a bunch of IF filters.

Best points:

  • The ability to survive in a crowded noise filled band.
  • Many bandwidths in each mode without having to buy additional filters.
  • It is also a well-thought out contest ra dio. The built-in antenna switch, so that two different antennas can be used, even in the same band.
  • The provision for an additional receiver to share the same antenna as the one currently in use by the 870. ■ One of the features we liked most was the ability to adjust the transmit voice frequency equalization and voice processing to produce the best sounding signal for an individual voice, and to monitor the results. The reports on the air impressed many.

• It was also agreed that the noise blanker (which is adjustable from the front panel) was also very effective.

• An innovation which also received a good review was the ability to program the receiver for a very fast AGC release time on CW. When working a weak DX station being called by very much stronger local stations, the re^ ceiver would almost instantly recover from the stronger stations.

• The antenna tuner is a real improvement over anything that Kenwood has offered in the past. First it’s very fast. Whether you’re just changing bands and the tuner is going to a memory location or you are attempting to match an antenna, it just takes a few moments to tune and stop.

The numbers in the book don’t indicate the apparent range of impedances that it is abie to match. I was able to match a twenty meter mobile antenna on both 40 and 15 meters as well as the intended 20 meter band. At home, a random length di-pole matched on most bands. Of course matching isn’t everything, a non-resonant antenna still is usually a poor radiator, and a tuner isn’t going to change that. In another novel change from the Kenwood past, the antenna tuner may also be used during receive. This will result in greater immunity from QRM caused by strong out of band stations, and if your antenna isn’t well-matched will raise the received signal strength. I had modified my TS-440S auto tuner years ago to do this, and found it be a worthwhile feature, especially when operating mobile.

The antenna tuner has 18 preset memory frequency segments. This enables you to have one setting for the CW portion of most bands and another for the phone portion, In addition you can preset either antenna connector 1 or connector 2 (ANT lt ANT 2) for the same portions. Frequency Bands While the receiver covers the entire range from 30 kHz to 30 MHz, the transmitter will not operate outside of the U.S. assigned bands—not by even ten hertz? MARS and CAP modification data will be available for those properly licensed.

This radio contains a 68 item menu, which enables you to set up the radio exactly the way you want it. This also eliminates many panel or hidden controls, such as VOX, CW pitch, display dim and more, There are actually two main menus, A and B, They are the same, and may be set separately for different situations such as normal operating and contesting. You can switch between them at will. Also you can assign the most often needed menu functions to a quick menu for fast access, without calling up a main one.

When you temporarily want to return the menu to the default settings, it can be done by turning off the power, holding the CLR button and turning the power on. To return to the original settings, turn off the power and turn it on again,

The front panel meter serves up to six different functions, and consists of a multi-colored curved bar graph, that looks somewhat like a mechanical meter. An unusual feature is that the relative bandwidth and position of the pass band tuning is graphically displayed. This is a really nice feature because it instantly shows how the receiver filtering is set up.

The receiver sports three new buttons which use the unique features of the DSP. The first button is AUTO NOTCH. This introduces an automatic very deep notch In the receiver IF to eliminate a heterodyne that may interfere with a SSB transmission. By doing the processing at IF rather than at audio, a strong carrier won’t capture the AGC, and reduce the desired signal s strength.

The second button is called BEAT CANCEL. Used on either SSB or AM this button enables an audio notch filter thai will reduce or eliminate interfering tones* This function is also more effective at removing low-level tones than AUTO NOTCH.

The third button is called NR or noise reduction. This uses the DSP on All modes except FM to improve the signal to noise ratio of received signals. A differ ent method is used on voice modes than is used in CW or FSK. An adaptive filter analyzes speech patterns and forms a variable filter around the received signal. Kenwood calls this method Speech Processing/Auto Correlation (SPAC). On CW and FSK the preferred method is the Line Enhancer Method or LEM.


Like any new product, some things will require time and experience to perform the best they can. The radio that I had for evaluation was a pre-production model.

and some of the minor things my fellow e valuators and I didn’t like may be taken care of in production:

• It will take some study and practice to master.

• The poorly contrasting display in sunlight.

• Lack of extending front feet.

• It was reported by some that the receiver audio was distorted and lacked adequate frequency response.

• The radio doesn’t include a power supply but requires a separate DC power supply capable of delivering 13.8 VDC with a current capacity of 22.5 A or more.

• An internal speaker is mounted on the top cover and it sounds all right, but I would recommend a good quality external speaker or earphones for serious operating. Buying a major piece of radio equipment such as the TS-870S (or any other radio) requires an informed decision on the part of the buyer. I would certainly sug gest that you spend some time in front of the radio, and see if it is able to do what you want it to. What seems wonderful to someone else, may not be what you need. Talk to others who have used the equipment and then make your own decision based on your own needs, tastes and experience.

A friendly piece of advice from someone who has worked on a lot of amateur radio gear: If you have trouble with a sophisticated radio such as this, don’t try to repair it yourself, and don’t take it to “Mr. Fixit”. There are very few service adjustments inside, and it lakes special tools, a lot of experience, good test equipment as well as the service manual to make it well again. This is no place for guessing and substitute parts.


First Licensed in 1956 as a novice (KN6YAZ, w hile in Jr. High School, Stuart Landau now holds an Extra Class License,K6YAZ. He has worked in commercial television, aerospace, and communications electronics* and is Mrrent ly working as an Engineer for Standard Communications Corp., working on land mobile radio and marine electronics products.

Mr. Landau would like to thank Randy Powell, NZ6N. Al Mandel WB6RGF and Ulrich Rohde KA2WEH for their help with the evaluation. And a special thanks to the people at Kenwood for the loan of the radio along with the documentation and software.

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