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Product Review Kenwood’s DCS-9120 100MHz digital oscilloscope Kenwood’s DCS-9120 programmable digital storage oscillo­scope provides both analog & digital modes of operation, with 4-channel 100MHz operation in the analog mode & two channels at up to 40 megasamples/second in storage mode. First impressions of the DCS-9120 are that it is a fairly compact unit with a front panel that has lots of knobs, buttons and control labelling. The knobs for vertical sensitivity and time­base do not have calibrations as their settings are displayed on the CRT screen, as is the triggering level and even the date and time if required. Most of the pushbuttons on the front panel are accompanied by backlit legends to indicate the selected setting. These are good because they give an unambiguous indication of the various settings. On the rear panel are ports for a pen recorder, plotter and an RS-232 serial interface. The DCS-9120 can also be controlled via a GP-IB interface so that it can be used for automated test­ing in production or other applications. Physical dimensions of the oscilloscope are 310 x 160 x 510mm, not including the tilting handle. Its mass is 10kg. When used in analog mode, the DCS-9120 functions as you would expect for a 4-channel 100MHz oscilloscope. Each of the four input channels has its own sensitivity adjustment from 5V/div down to 1mV/div and an uncalibrated variable knob can be used to vary the sensitivity within these ranges. In addition, the 100MHz bandwidth of the oscilloscope can be reduced to 20MHz to reduce noise on the display when signals below 20MHz are being measured. Signal coupling of the inputs can be 88  Silicon Chip DC, AC or grounded, while both the channel 2 and channel 4 inputs can be inverted as well. This feature can be used to provide a differential input mode by ADDing channel 1 to channel 2 or channel 3 to 4. Each input socket incorporates a detector which automati­cally adjusts the sensitivity (Volts/Div) reading on the screen whenever the supplied PC-31 probes are switched to 10:1. If other brands of probes are used, you will have to resort to mental arithmetic to multiply the sensitivity by 10 when 10:1 is selected on the probe. Sweep time is selectable from 20ns/ div to 0.5s/div in 23 ranges, with fine adjustment and x10 sweep magnification avail­able. Timebase modes are A, B or delayed trace, A intensified by B, A and B alternating or X-Y mode. The delay between the A and B timebases can be either a continuous delay, a trigger delay or a count delay. Triggering modes Triggering modes are Auto, Norm, Single and Fixed, with the usual CH1CH4 source selection or line frequency triggering. You can also select Vert triggering which automatically triggers on the lowest selected channel number. No external triggering input is provided. Coupling for the trigger signal can be DC, AC, High Frequency Rejection or TV (line or frame 1 or frame 2, NTSC or PAL). Horizontal or vertical cursors can be displayed on-screen to enable voltage, period and frequency measurements, a fairly standard feature of scopes with CRT readouts. Menus Apart from the front panel controls, there are many func­tions and operations that can be accessed via the menu options. The five menu subsets are Processing, Memory, Set, Output and Option. Some functions selected via the menus are only available with the storage facility. For example, if you select the average display from the processing menu, it will not operate in the analog mode. The averaging feature is very useful for improving the signal to noise ratio of the displayed signal since it filt­ers out random noise. Averaging can be selected from between 2 and 256 waveforms. Other functions available from the processing menu are interpolation (off, linear, sine and spline), calculation (+, -, x, /) between channels, and peak detection of maximum, minimum or both. Memory menu options allow you to select the display ad­dress, memory size and reference memory. The latter is a memory space into which a waveform can be stored, to be recalled at a later date and compared with another waveform on the screen. In the Set menu, you can change the delayed triggering options to be displayed in divisions or real time (seconds). You can also set the type of TV triggering, buzzer modes, display offset and time display modes and settings. The Option menu provides programming features so that on-panel settings can be stored, comments can be made on-screen and the present status displayed. A parameter sub menu provides selection of automatic calculations which can be done by the oscilloscope and then displayed on the DCS-9120 The DCS-9120 provides both analog & digital modes of operation. In analog mode, its bandwidth is 100MHz, while in digital mode it can operate at 40 megasamples/second. Many of the functions are accessed via menu options. screen. You can only select one per trace but each trace can have a different parame­ter displayed. The parameters selectable are period, frequency, pulse width, rise time, fall time, delay, overshoot, undershoot, peak to peak, RMS volts, top level, base level, amplitude and power. Digital storage Switching from analog to digital modes is as simple as pressing the Mode switch. The difference in the storage mode is clear, however, if you need to manipulate the display. You can magnify the stored waveform by up to 100 times or compress it to 1/ th of the original, depending on 10 how you want to observe the signal. You can also perform arithmetic operations between traces and set up peak hold for catching glitches as little as 50ns wide. Strangely enough, you can also observe the waveform before the triggering point. This is a feature only available on storage oscilloscopes and is possible since the storage of the waveform is continuous and the triggering point really only tells the scope what part of the waveform you want to observe. Conse­quently, you can observe the waveform before or after the trig­gering point, depending on whether post or pretriggering is selected. The other interesting feature is the way the storage memory can be set up. There are two separate 16K word waveform memories for channel 1 and channel 2. One is called the acquisition memory and the other the reference memory. Each word is eight bits wide. You can set up the memory to be 2K words long for eight screens of storage, or 16K words long for storing a large continuous waveform section. Storing waveforms As is the case with most storage oscilloscopes, it takes some time to become familiar with the operating features. A lot of the difficulty was due to the extraordinary number of options that are available in the storage mode. However, we found that digital storage was particularly useful for catching glitch­es and for observing non-repetitive waveforms such as the firing of a fluo­rescent tube – virtually impossible to observe on a normal analog scope. We had a minor complaint when using the Delta REF/DLY TIME rotary control to scan through the eight x 2K memory blocks. In operation, the delta V cursor switch was often accidentally bumped due to its close proximity to this control. The instruction manual for the oscilloscope is good although there are spelling mistakes and strange English in some parts. However, all the features of the oscilloscope are well explained and examples are given for both analog and digital storage modes. Overall, we liked the features of the DCS-9120. It provides the best of both types of scope; the fine detail waveforms in the analog mode and the facility to store and manipulate waveforms in the digital storage mode. The ability to print out waveforms and control the unit via the GP-IB interface also help make this oscilloscope a very versatile unit. It should appeal to a wide variety of users for laboratory, test bench and production use. The Kenwood DCS-9120 is priced at $9308 plus 20% sales tax if applicable and it comes with a 12-month warranty. For further information, contact the Australian distributor for Kenwood test equipment, Nilsen Instruments, 18 Hilly St, Mortlake, NSW 2137. Phone SC (02) 736 2888. (J.C.) January 1994  89