Nuts and Volts - October 2015

Gaussian noted above. Known as the “cliff effect,” upon reaching the end of their stated bandwidth, the signal rapidly drops off to nothing and does not stretch out the usefulness as the Gaussian would.

I have only had occasion to use these newer scopes a couple of times. What I loved about them was the ability to store wave forms in memory for later comparison, and also to display and hold very long period wave forms. However, I felt there was too much clutter and information on the display which — at least for me — bothers my concentration on the one thing I am looking for. Most of the time, I like to see one quick trace and move on.

What to Buy and When to Build

As stated earlier, there is just no substitute for high quality test equipment, but there are many instances where it is very justifiable to build your own. Again, I would definitely recommend you build your own power supplies as needed over time. With today’s chips available for that purpose, superior performing supplies can be built easily and cheaply to exactly suit your own requirements. Other reasons would include the following: • TE that you cannot afford at the time, but can use a decent “starter” unit.

• TE that you only have need for occasionally, for non-critical tests.

• TE where you only need the very basic functions.

• TE for one specific testing purpose.

The above TE would include, for example, simple function generators of limited high-end frequency; RF generators for limited tests such as a 455 kHz and 10. 7 MHz IF generator; basic multi-waveform generator; current sources; and test jigs just to name a few. There seems to be an application specific chip available to get you started for any of the items you would want to build.

Other very doable and useful projects could be timers, period counters, and metered variacs just to name a few. In fact, there are only two items in my basic list that you would never want to attempt: the DMM and the oscilloscope. All the rest can be built to fairly decent standards. There is just a personal gratification in completing a useful and professional looking project that can’t be described.

One point about construction that I consider mandatory is a practical and handsome enclosure and front panel with neat artwork. I see so many DIY projects that never get past the solderless breadboard with leads and controls hanging off of it in a totally ugly fashion. It leaves you guessing what does what. For my money, I • 0.02” — Shielding and small subassemblies • 0.03” — Small panels and cover plates • 0.06” — Front panels, cover plates, and small chassis • 0.125” — Chassis only Along with common hand tools and a pop riveter, a small nibbler tool (about $7 - $8) comes in handy — especially for square holes. That and a “poor man’s brake” (made from miter-edged 1x lumber clamped into a bench vise as described in some of my previous N&V articles) completes my so-called sheet metal shop.

As to TE circuits available, the Internet is full of them, along with numerous magazine articles over the years. You could even peruse past editions of N&V under my name for several that I have contributed. I guess the final factor here is not so much what you can afford to buy, but rather what you can justify to buy. This will be the predominant answer in the buy/build decision.

Conclusion

I hope this article has given a better insight on the why, when, and how of test equipment for your bench, and some of the caveats to look out for. I know I may catch a certain amount of flak here for some of my thoughts but it has all stemmed from my real world experience, and that I cannot deny. For some, they may think the older equipment I favor is junk, but this has all proven to be high quality TE, and foremost, it is repairable by most enthusiasts. Granted, the newer TE specifications may far exceed the performance of the prior, but are those higher specs necessary for most of us?

Consider two things here. One is repairs that I am sure even the best of us could not accomplish. This alone could be double the cost of the original purchase price. Two is directed toward highly accurate pieces of TE. Accuracy does not come cheap. Also, the stated high accuracy at the time of manufacture is meaningless down the road without periodic calibration checks — an expensive proposition.