On 10/27/2010 10:17 AM, Jim Brown wrote:
> On the show floor, it is often easy to spot them with a visual
> inspection. What you're looking for is a shield connection that goes
> directly to the shielding enclosure.
I forgot to mention that it is also often possible to find Pin 1
Problems in an active demo with a 2M and 440 talkie. I use a Kenwood
TH-F6A. I key the radio off and on, moving it along the interconnecting
cables to find hot spots (due to wavelength effects). I'll typically
hear both the switching transient and some hum/buzz in the susceptible
equipment. A TDMA cell phone (like Nextel) is also a very effective RF
injection probe near 900 MHz, because it's pulsed modulation of a 1W
carrier with a repetition rate near 220 Hz, which places harmonics of
the detected modulation in the middle of the speech range.
It's important to realize that RFI susceptibility varies a LOT with
frequency, thanks to many circuit variables (stray L and C) and to
circuit geometry that causes addition and cancellation at various
frequencies. The AES paper shows measured data for a half dozen pro
products. These single-frequency injection probes are telling only part
of the story -- they're a pin hole through which we can view the elephant.
73, Jim Brown K9YC
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