I was going to substiute an ac to dc adapter for one which had gone bad. The substiute has all the right specs, except that it is missing a cylindrical rubber collar that the original had situated near the plug. What is the purpose of this collar and is it necessary that a substitute have it as well? Thank you in advance.
A fairly thick collar (1/4" to 1/2" thick, and perhaps twice as long), and fairly heavy for its size?
If that's a fair description of how it looked, it was probably a rubber- or plastic-coated ferrite cylinder, through which the wires ran. Ferrite cores of this sort are used to reduce the amount of radio-frequency energy which travels along the cord, so that the RF isn't conducted or radiated into places where it will cause interference with radios and televisions. Technically it's probably a "common-mode choke".
The fact that the original adapter had one, suggests that the manufacturer of the equipment it's used with felt (or learned) that there's enough RF leaking out of the equipment through its power supply jack that an RF suppressor was necessary in order to meet FCC emissions standards. If you use a replacement adapter without a ferrite, there *might* be enough RF radiation from the cable to cause a problem for somebody. Or, possibly not.
You can buy small two-part "snap-on" ferrites at electronics stores and add one to your new adapter's cord. Just open the two halves of the ferrite, run the cord through the center twice (wrapping it around the outside of one half of the ferrite once), snap the two halves together, and you'll be good to go.
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Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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Thanks Dave. I appreciate the reply.
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