Re: Good USB Cables #usb
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jdow
Consider two things, ground loops and capacitor
bypassing where possible.
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The ground loop can be a total killer at AF and a serious problem at HF. Try to find ways to deal with it. It's often not at all simple. Capacitive bypassing is a good thing, too, when you can do it. Attenuation comes from either or both increasing the impedance of the path into a device and decreasing the input impedance. If your input impedance is 1k it is going to take a few pounds of suitable ferrite to attenuate signals. If your input impedance is 50 ohms and the impedance of your chokes is 10k your attenuation goes from about 20 dB to almost 50 dB. This input impedance would be your common mode input impedance, of course. So it is likely to be quite low at least for the shield side. Ferrite can help guarantee that noise on the shield has less chance to leak inside. (All cables leak RF. All you can do is negotiate with it over how much it leaks.) Something to think about it the fact that if you have one ferrite over a cable and add a second beside it, all you do is double the impedance (6dB). If you can find a way to let cable between the chokes have a low impedance path away from your receivers (and lips on microphones) then you can go from doubling the impedance to having cascaded low pass filters with a 20 dB filter plus a second 20 dB filter giving you 40 dB rather than only 26 dB. Design your solution rather than throw ferrite at it at random. A really good resource to visit is Jim Brown's website. He spent his working life fighting emi and hum in a theater inside a building in Chicago that housed several very high power radio and TV stations - and making it work. He knows what he talks about. {^_^} Joanne
On 20211119 07:43:20, Tom Crosbie G6PZZ
wrote:
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