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Author Topic: RF on USB  (Read 4691 times)
NU9J
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Posts: 109




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« on: May 24, 2014, 11:23:34 AM »

Will a standard double-choke USB cable keep RF out of a computer?

Due to the constraints of my setup, my computer is located within a few feet of my antenna. I am using a Ensemble RxTx, but I have a problem in that if I push the output over 0.5 W, the computer tends to lose USB communication with the radio. I suppose too much RF is coupling into the cable. I am considering this cable

http://www.amazon.com/dp/B003MQ29B2/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=1QKK8ZOTKR0NT&coliid=I3BBXFPVHK5WXS&psc=1

and wondering if those chokes will do a decent job. Any experience/suggestion welcome. Thanks!
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~Philip
KI6LZ
Member

Posts: 599




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« Reply #1 on: May 24, 2014, 03:26:18 PM »

Only way to find out is to try it. No magic analytic method.
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AA4PB
Member

Posts: 12983




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« Reply #2 on: May 24, 2014, 04:08:07 PM »

Too many variables to tell. Just because it works for one setup doesn't mean that it will work for you. As a general rule however, I think these ferrites are intended to prevent RFI generated by the computer from being radiated by the cable. I wouldn't expect them to be too effective at HF frequencies.

You might try sliding some shielding over the cables and grounding it to the computer chassis. First try leaving the far end floating.
« Last Edit: May 24, 2014, 04:11:24 PM by AA4PB » Logged
WX7G
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Posts: 6204




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« Reply #3 on: May 24, 2014, 06:40:14 PM »

Is the Ensemble in a metal box? 

The USB issue could be at the PC end or at the Ensemble end of the USB link.
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CHRISTOFERO
Member

Posts: 24




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« Reply #4 on: June 01, 2014, 02:40:17 PM »

Are you using a balun? (or unun, for a long wire)  Also maybe check your SWR? Also, how are your grounds/grounding? Grounding is extremely important for best results with any SDR. Perhaps set up some kind of one point grounding, make sure your computers case is also grounded - Ethernet switches, etc.too. Also, where the coax comes into your shack, you should have a good ground there too. Use the thickest wire you can that's manageable. Ground it to ground rods, or cold water pipes that are solid metal. (not PVC!!!) Ask an electrician as to the code.

Also, you can and should loop the USB through ferrites as many times as they will fit for HF. You can also use toroids, and loop it again as much as will fit. Type of toroid will matter a lot as to what frequencies will be attenuated the most.
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ZENKI
Member

Posts: 980




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« Reply #5 on: June 07, 2014, 05:29:27 AM »

You can buy a test equipment ISOLATED USB cable which will isolate the cable from the PC.

http://www.bb-elec.com/Products/USB-Connectivity/USB-Isolators/USB-Isolators.aspx

You can also build one.

If you do have common mode issues in your shack you would be far better off fixing with things like a single point ground, proper antenna design and then common mode chokes.

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