Archive for November 2014

Visualizing Comparator and Op Amp Hysteresis

Hysteresis can be added to a comparator circuit to improve its stability, especially when the input signal is noisy. In this post, we will examine the hysteresis characteristics of some common comparator and Op Amps using an oscilloscope. Continue reading ‘Visualizing Comparator and Op Amp Hysteresis’ »

Testing an RTL-SDR Spectrum Analyzer

Using software defined radio such as the popular RTL-SDR (1, 2) as a spectrum analyzer is nothing new (examples can be found on HackADay and EDN). In this blog post, we will discuss some of the do’s and don’ts when using SDR as a spectrum analyzer and look at some measurements I took using the popular NooElec SDR based on Realtek‘s RTL2832U DVB-T demodulator chip and Rafael Micro‘s R820T tuner chip. Continue reading ‘Testing an RTL-SDR Spectrum Analyzer’ »

Keithley 197 Battery Option Build

I have been quite happy with my fixed-up Keithley 197 5 ½ digit bench meter purchased from eBay (you can find the teardown pictures here) earlier this year. Keithley 197 has a battery pack option (Model 1978), and this option allows it to run on battery power for 5 hours without having to plug into the mains. While it is far from being a truly portable meter, its performance easily surpasses most hand-held multimeters. So I decided to build the battery option myself and hopefully I would be able to use the meter more often in places where power outlets are not available. Continue reading ‘Keithley 197 Battery Option Build’ »