[Amps] construct ferrite "line isolator"

[Jim Brown]

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