Noise reduction: separate 5V wire (USB) for an SDR

[kellogs]

Given a well shielded and choked USB cable:

On an SDR that draws its power over USB, would there be any good in supplying it with the cleanest 5V that I can come up with over the red wire while keeping D- and D+ wires connected to the Raspberry Pi (or other computer) USB port ? And if yes, how should the GND black wire be treated ?

Or perhaps it is useless due to noise getting into the SDR dongle via the differential pair anyway?

 

[Dirk_SDR]

In my setup there is also noise over USB power.
A good solution was:

iDefender3.0 by iFi audio - Protect against Ground Loop Noise & Noisy USB power

Defender of the earth. Multiple plugs and ports produce separate earth points, creating an unwanted chain of buzz and distortion. The iDefender3.0 plugs into your USB port, injects super clean 5-volt power and creates a single earth point for faster, cleaner sound quality.

ifi-audio.com

... together with a clean audiophil power supply like:
iDefender3.0 by iFi audio - Protect against Ground Loop Noise & Noisy USB power (5V version)

 

[Dirk_SDR]

Sorry, 2nd link should be:

iPower2 by iFi audio - Ultra Low Noise DC Power Supply with international options.

Power up your system. Upgrade your existing power supply to the iFi iPower2 to flood your system with quiet, noise-free audiophile-grade clean power.

ifi-audio.com

 

[kellogs]

The iDefender does no galvanic isolatation on the data lines, but the iGalvanic does:

iDefender3.0 breaks groundloops (which is however where > 90% of the benefit of a galvanic isolator over other "gizmo's" comes from) and only that. It is not a galvanic Isolator.

iDefender3.0 (Official) - USB Ground Loop Eliminator

iDEFENDER3.0 The iDEFENDER3.0 solves the common ground loop/hum. It ‘breaks’ the ground loop but in a, proper and electrically safe way Just add iPOWER 5v to inject clean power at the source. Break ground loops the correct way. iDefender3.0 with IsoEarth® Use upstream at the audio source. Because...

audiophilestyle.com

The iGalvanic3.0 features two distinctly separate galvanic isolation stages. One for USB3.0 and the other for USB2.0. They CANNOT be the same because the fundamental architecture is different:

1. USB3.0 has separate transmitting AND receiving lines.
2. USB2.0 is bi-directional, on one SHARED line.

iFi Audio iGalvanic3.0 - The Holy Grail of Audio

Part 1: iFi Audio iGalvanic3.0 - The Holy Grail of Computer Audio In “The Last Crusade” in a cavern full of cups, Indiana Jones had to choose the Holy Chalice used in the last supper. In USB audio, similar propositions are abound as selecting the best device to improve USB computer...

www.head-fi.org

So, if the iFi support guy is to be trusted, then just breaking the ground loop accounts for over 90% noise reduction over USB.

So then yes, providing a quiet +5V / GND pair is the way to go. Am I right?

 

[merlin]

One solution I tried was an OTG cable (short) one plugged into the computer, one plugged into a hefty Anker battery, and one for the SDR.
That took the load off the computer USB 5 v. Very clean.
Another clue, is disconnect and use a short acoss the antenna input (Be sure bias T is off) any noise spikes will be internal to the SDR and no fixes for that.
For the short, I use the short calibation SMA from my Nano VNA.

 

[Pape]

Did something similar here. I'm having multiple dongles therefore I cut the 5v- and 5v+ between the usb uplink to the computer and provided a clean source to the hub itself. It was not done for noise but more for modularity of the setup.

 

[Omega-TI]

Yes, grounding independent from the PC can reduce noise, but what about the data lines from the SDR to the PC? Would that not also be a conduit of RFI?

 

[Pape]

it is shielded and well the data is in digital format therefore if you get noise in the digital signal you will end up with corruption