Needless to say, we had neither paper nor napkins. We welcomed the good, strong, cheap, untextured toilet paper of the second-rate motels. One and a half rolls later, we had a design that worked the first time and was in production for several years. As the only engineer, aside from the boss, I was given the job of putting it on real paper as soon as we returned from the trip. It was reduced from 152-ft. by 5-in. toilet paper to two "D"-sized sheets
Stanley S. Friedman
DRS Communications Company, LLC
Author replies: The basic requirements for a signal source for testing high-speed ADCs are that it has low phase noise (jitter) and produces a signal of low distortion. The low phase noise isn't a problem for many signal generators, but the low distortion requirement is a real problem, even for the best generators available. For this reason, I suggest a bandpass filter between the generator and the ADC input.
We have found the TTE "LE1161" series of filters to perform well. They have a 3-dB bandwidth of 15% of the center frequency. We found that the TTE filters produce a good, clean sine wave with a stable square-wave input too. We use the HP 8662 signal generator, but inexpensive generators also perform well when used with the TTE filters, as long as the generator doesn't have significant phase noise. You can tell if there's a lot of phase noise as "spreading" will be seen around the base of the carrier in an FFT plot. This spreading looks kind of like a pine tree and is often called a "Christmas tree."—Nicholas GrayThe Industry Still Has Ethics Though I have no need at present to blow a whistle, I really enjoyed the implied ethics in your column of the Aug. 7 issue \["Whistle Blowing: Should I? And How To Do It Safely," p. 150\]. It's good to hear of people with deep experience in the industry that really care about ethics!
Try as we will here (LANL), the real academics of ethics needs to be thrust upon organizations, such as the DOE, the FBI, and Congress, if this country is to maintain any kind of motivated and talented crew at the National Labs. That's a subject too involved to get into here, but thanks for your article.
Response: The concept of vector addition of uncorrelated variances is pretty solidly accepted even within Boeing where it's used every day to do statistical analysis of mechanical stack-ups. It also lurks behind signal processing techniques, like boxcar integration, where we improve signal to noise on a repetitive signal because the signal is correlated and noise is not. It has been used in project planning for at least 40 years. Nevertheless, from the tone of your message, I suspect that I'm not the person to convince you of this.
Happily, we both agree on the value of "figuring out what's going on so that you can take action to resolve problems." I'm sorry that my column wasn't more convincing.—Don ReinertsenDon't Let Marketers' Lingo Fool You Just to keep things technically straight and not propagate misleading information (being the exacting engineers that we are), "brightness" is perceived and can't be measured \["Both Larger And Smaller Sizes Are Fueling The Innovation Of Flat-Panel Displays," Aug. 7, p. 83\]. "Luminance" is measured and, therefore, has associated units, such as nits, foot-lamberts, etc. Contrast ratio is then a ratio of luminance values. For some reason engineers have picked up on the marketers' cop-out and continue to promote this incorrect terminology.Randy Pyles