Gameboy Oscilloscope （3）

Published:2011/8/1 3:00:00 Author:Amy From:SeekIC

More megahertz

Next we have three analogue oscilloscopes with a band­width of 100 MHz. As expected, all three perform a good deal better than the less expensive instruments. This shows once again that it’s too simple to just compare specifications. We’d like to reiterate that it’s quite proba­ble that the models of the brands in the previous group with bandwidths of 100 MHz (or more) would also per­form much better.

The larger bandwidth increases the quality of the dis­played test signal. Not only is the image sharper, which makes it easier to distinguish rapid changes, but the writ­ing speed of these instruments is also quite a bit higher. The display is refreshed more often, making the image considerably more steady on the screen.

The Hameg 1004-3 and GW Instek 6103 are microprocessor-controlled. The advantage of this is that certain settings can be stored in memory. In situations where a number of similar signals must be regularly mea­sured, that can save a considerable amount of time. However, it also has drawbacks. For instance, it some­times takes a bit of searching to find out exactly how the instrument is configured, and displaying the various set­tings on the screen affects the displayed waveform. The latter factor is sometimes annoying with the 6103.

The Hameg and GW Instek instruments also allow mea­surements to be made on the displayed waveform using cursors. We think that once you’ve worked with cursors, you’ll miss them if your scope doesn’t have this feature. If your budget permits it, this function is thus to be recom­mended.

The Leader LS8105A does not have cursor capability, but a 100-MHz scope with cursors is also available under this brand name. With regard to the LS8105A, we noted that it is pleasantly easy to use, solidly built and has outstanding image quality. The accompanying manual is not brilliant, but that’s actu­ally the only criticism.

Digital or analogue?

The Voltcraft 650AD and Hameg1507-3 are combined instruments. They are actually ’normal’ 50- or 100-MHz scopes (respectively) with addi­tional digital storage scope capability. This directly overcomes one of the most significant drawbacks of digital scopes, which is that a purely digital oscilloscope can never display the actual waveform. What it displays is always a reconstruction of a sampled signal. As a result, it can happen that the image on the screen has no resemblance at all to the measured signal. With a combined scope, you can always quickly check whether the digital result is accurate.

In this regard, we must note here that the digital capability of the combina­tion models included in this test is only limited. They have several cursor func­tions for making measurements and can be operated via a PC, but the sampling rate is actu­ally too low for good reproduction of a signal such as our test signal. In practice, the specified bandwidth is thus only usable in the analogue mode. Another factor is that the noise contribution from the A/D converters is generally rather large. This causes the traces of digital oscilloscopes to be ’fatter’, so details more quickly become literally lost in the noise.

Other than that, there are no remarkable differences or details to be reported with regard to these combined instruments, and the performance of the analogue portion is good.

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