Re: Good USB Cables #usb


jdow
 

Consider two things, ground loops and capacitor bypassing where possible.

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:

“Ferite the true friend of the Radio Ham”

 

True, but it has to be the right type of ferrite to be effective. Putting your own ferrites on your cables means you have a much better solution for solving EMI/RFI  problems.

My shack is groaning under the weight of ferrite in place, much of it doing nothing because it is cheap Chinese ferrite bought because it fitted the cable more than anything else.

I have a big EMI/RFI problem which is slowly diminishing as I replace both cables and ferrites to make better common mode chokes and filters. Using a trusted brand is a good start but does anyone know the type of ferrite fitted to the Tripp Lite leads that started off this discussion? I’m just curious.

 

Tom G6PZZ

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of John Cliff
Sent: 18 November 2021 17:06
To: main@sdr-radio.groups.io
Subject: Re: [SDR-Radio] Good USB Cables #usb

 

Good call there OB. Ferite the true friend of the Radio Ham. 73 de John - G0WXU.

 

On Thu, 18 Nov 2021 at 15:13, jdow <jdow@...> wrote:

VGA cables do this, too. I am not sure about HDMI. There are a lot of HDMI cables with glowing advertising and claims that aren't really up to snuff. Linus Tech Tips has the testing on youtube. I am guessing much the same goes for USB3 cables and Ethernet cables and....

{o.o}

On 20211118 06:53:29, Kriss Kliegle KA1GJU wrote:

It’s not just USB cables that have poor RFI shielding. I was just at another Ham’s QTH installing an over the air TV antenna for when the power/cable goes out. When ever he turned on his IC7610 with the external video monitor, he would loose TV reception. TV antenna was in attic and rig in basement, separated by +35’. On a hunch, I disconnected the DVI Cable from the IC7610 (that contains toroids on both ends) and TV reception returned. I placed a few random, unknown value clamp-on ferrites that he had in a drawer and all was well.
   The hunch was from prior experience with a DVI cable in my main operation position, the computer monitor wipes out certain 440 band channels on my 2m/440 rig.

   Those with DVI cables in operation and use 70cm and above may want to experiment with ferrites.

YMMV (Your Milage May Vary)

73 Kriss KA1GJU/AM

 


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