Keysight has a new application note—5 Common Mistakes to Avoid When Buying a Low-Cost Oscilloscope—that you might want to get if you’re going to buy a scope, or even if you use a scope. This free app note covers the following five topics:
- selecting an oscilloscope with insufficient bandwidth
- settling for a USB oscilloscope
- underestimating usability
- running the risk of equipment support difficulties
- focusing solely on specifications
Make sure you have enough bandwidth
A scopes’s bandwidth is the frequency at which the input signal sine waves attenuate by -3 dB (30%) as shown here:
From a practical point of view, what this means is that if you need to measure the amplitude of a 146.96 MHz signal with some accuracy, don’t settle for a 150 MHz scope. The amplitude measurement at that frequency could be up to 30% off. You’ll probably want to purchase a scope with at least 200 MHz bandwidth to make that measurement.
And, when measuring digital signals, having a scope with a high bandwidth is especially important. The reason for this is that while a digital signal may have a relatively low frequency, they contain higher frequency components. Keysight recommends choosing a scope with a bandwidth at least five times the highest clock rate in your system.
Don’t settle for a USB scope
USB scopes are generally cheaper than stand-alone scopes with similar specifications, but remember that you’ll need a computer to provide the user interface. For one thing, it’s not going to be as portable as a stand-alone scope.USB scopes have their place, but probably not for general-purpose use.
Don’t underestimate usability
Even if you only use a scope occasionally, or perhaps especially if you only use a scope occasionally, consider the usability of the scope you intend to buy. Keysight notes that there are several factors contribute to an intuitive and detailed graphical user interface (GUI). These include display quality, display size, resolution, update rate, viewing angle, color versus monochrome, and user-specified display modes such as variable and infinite persistence. Additionally, a multi-language GUI can better contribute to the user’s interaction with the oscilloscope. Ideally, you’d like to be able to play with a scope for a while before buying it.
Make sure that you can get support
Before you plunk down your cash, make sure that you can get support should the scope you buy be DOA or fails after you start using it. Research the support and services offered by the vendor before buying to avoid these issues. A cheap scope with little or no support is not a bargain.
Don’t focus solely on specifications
Keysight warns, “Specifications do not tell the whole story. You need to dig deeper, read between the lines, and ask questions when researching oscilloscopes to select one that best fits your needs.”
Ask your friends what kind of scopes they have and if they like using them. You can also head over to the EEVBlog Test Equipment Community Forum. It now has more than a half million posts (!), and test equipment nerds from all over the world hang out there.
This is just a quick review of the Keysight app note. I’d suggest that you download and read the entire thing before buying your next cheap scope.
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