The LA-22 Low-Noise Laboratory Amplifier, 800 Hz–22 MHz, 1.1 nV / √Hz

One problem that comes up again and again in doing measurements is that we need the apparatus to be quieter than the thing we're measuring, ideally by at least a factor of two.   Besides quiet, it should be wideband, have an accurately known gain that's flat with frequency, have a clean step response, and generally do its job while keeping itself out of the way.  There's a wealth of detail in our app note AN-1 on photoreceiver testing.

A quick plug for a little gem of a book that all fans of early radio should know about: "Super-Regenerative Receivers" by J. R. Whitehead (Cambridge University Press, 1950).  It's part of the Modern Radio Techniques series, where a bunch of the technical movers and shakers document the advances that were made during the war, e.g. centimeter radar.  This one is about the theory and practice of superregenerative radios.  I learned a lot from it and had a lot of fun.

Temperature Control

The need to control temperature is everywhere, but getting it right is more difficult than one might expect. A domestic furnace controlled by a simple thermostat keeps a house comfortable in winter, but the inside air temperature swings irregularly over a range of a few degrees. That's fine for a house---you can have a New Year's party, with a bunch of people dissipating a hundred watts each, doors to hot ovens and the cold outside opening and closing, no worries whatsoever.  The heating system keeps it comfortable.

In a previous article, we described an ultralow-cost time-domain reflectometer (TDR) that  is used as a radar dipstick for fuel gauges in heavy equipment.  Its 150-ps edges were better than good enough, and its rock-bottom BOM cost ($1.30 @ 100 pcs) made it possible for the whole gauge to retail for under $40.  That performance is far from the limit for low-cost samplers, as we'll see.