Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

jdow
 

Screening is good. Breaking ground loops, AF or RF, is a good thing, too. Ferrite makes the ground loops lossy as it breaks them. This is sort of the best of both worlds. And there is something to be said for keeping RF that is outside of cables where it belongs, on the outside of the box. So making a good electrical bond from each of the box's connectors to the box itself may provide you with a quite worthwhile improvement in behavior. It should not make it any worse. (And done carefully it will not change the cosmetics of the box. Braided shield from small diameter coax is a nice tool for this. Clean the inside of the holes and the inside of the box for the 10 MHz ref (AirSpy only) and USB connector holes. Then when installing the cover mush some of the braid between the edges of the hole and the connector shield. For the RF clean off a space just to about half way to the outside of the lockwasher. Then when tightening it you will get a nice ground to the coax shields for the RF input connector(s).

Also, unless you are running a very low efficiency antenna at HF, test for the interference when the band is open. If you cannot see it then it doesn't matter even if you can see it with a 50 ohm dummy load and with a small test signal present.

{^_^}

On 20180313 21:32, Ian DXer wrote:
Hi Dana,
Pleasing to read your report on your success with the Volutz USB cables.
I was looking at the Volutz Facebook page & I note that Volutz have just released a new Apple Lighting Cable.
For noise immunity I like the metal shroud that links the foil shield of the cable & surrounds the connector & components
underneath. One also gets a better look at the dual cable shielding from the drawing on the Facebook page.
Are these SMD components part of the lightning spec or are they part of Volutz's attention to EMI/EMC or impedance
matching?
I see a similar shroud on their USB C cable from their Facebook page.
What's not clear to me is if Volutz use a metal shroud on their connectors for their USB 2.0 to micro USB cables or
any filtering SMD components (if that's what they are?) similar to their new Apple Lightning Cable.
The Volutz website is scant with close up pics & tech data.
A further improvement to their USB 2.0 to micro usb cables would be to have a foil shield between the data & power pairs.
I purchased a replacement USB cable (CableCreation/Xillie) from the Internet last week. It arrived on Monday. It is supposedly triple shielded, but I suspect these are 'just
words' from a Chinese supplier via Amazon. I compared the the noise performance between AIRSPYHF+ supplied USB cable with my own
added mix of ferrites attached, also a Samsung USB cable, the CableCreation USB & the CableCreation Lead with a mix of ferrites.
Test freqs were roughly every 1MHz between 2 & 30MHz. Conclusions: I didn't gain the results I expected from the CableCreation USB cable, results were
similar to the plain Samsung Cable. But what brought best results was having ferrites on either the existing AirSpyHF+ USB cable or the CableCreation USB cable (similar results).
That said, for my own electro smog environment results were typically only a 2dB improvement to noise floor for the USB cables with the ferrites attached.
But on the better end of the results scale 'on some' frequencies I noted a 6-10dB improvement (with ferrites).
I'm sure if I purchased a better screened USB cable (similar to the standard of my router CAT6 S/FTP patch cables) I should hopefully see better results.
Every dxer has a unique RFI environment with their own unique challenges, some requiring a huge investiture of time & effort (mine's only in the early stages).
Our new Samsung refrigerator is the latest to be added to the RFI hit list (I'll try to mute my grumble).
73
Ian

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