[arm-allstar] BBB URI USB-HUB Distorted Audio

[David McGough]

Hi,

What kind of radio / repeater are you interfacing with?

In my experience, if the noise is low frequency (60 cycle hum), you've
probably got a ground loop. If the noise is much higher frequency (perhaps
1 or 2 khz) and jumping around a bit, the source is probably a noisy
switching power supply.

I've frequently seen ground loop woes using URI adapters when installing
them in repeater racks. In fact, I now modify ALL URIs that I install on
repeaters and add a large ground wire. This has 100% solved all ground
loop issues I've had thus far. Here are some sample photos of a modified 
URI. I'll attach the ground directly to a chassis screw on the back of the 
repeater.

http://www.hamvoip.org/kenwood-TKR/P1030817.JPG
http://www.hamvoip.org/kenwood-TKR/P1030820.JPG

For high frequency noise (switching power supplies, etc.), the best
solution is to find a quiet power supply. Note that many wall-wart style
switchers have several volts of high frequency common-mode noise on the
outputs. This can be easily seen using an oscilloscope.

I've used USB isolators in MANY installations where I had stubborn noise
issues--particularly where I had a noisy computer power supply (which
introduced noise into the USB signaling and URI), and couldn't easy
replace the power supply (this is more frequently seen with embedded PC's
than BBB's) . I've got about a dozen of these installed on repeaters and
remote-base radios:

http://us.hifimediy.com/index.php?route=product/product&product_id=69

I hope this helps a little. I've also got photos showing the grounding 
config that I've "standardized" on for BBB installations, if needed.

Happy New Year!


73, David KB4FXC


On Thu, 1 Jan 2015, Randy Neals wrote:

> I've been experiencing a distorted audio problem while setting up a BBB
> with powered USB-HUB, DMK URI, and USB Keyboard.
> 
> The audio distortion is noticeable on audio from the node. (transmit audio)
> To eliminate/isolate the issue I swapped out the URI for a SYBA USB Audio
> FOB and PC speakers.
> Still the same background hum/distortion. So that eliminated RF
> interference, ground loops, the URI and the radio.
> 
> Through further elimination, I have identified that when my USB keyboard is
> connected to the USB HUB, the hum/distortion is louder. (URI through USB
> HUB to BBB, no Keyboard)
> 
> And then have compared the audio when not using a USB hub at all, and I
> think there is a further improvement in audio, although not as major as
> when the keyboard is /is-not connected.
> 
> My next troubleshooting step is to swap out the keyboard, and then swap out
> the USB HUB.
> 
> The USB Hub I'm using is an AmazonBasics 4 Port USB 3.0 Hub with 5V/2.5A
> power adapter
> 
>    - Package includes: 1 USB 3.0 4 Port Hub / 1 5V/2.5A Power Adapter / 1
>    built in 10 inch USB 3.0 cable / 1 Owner's Manual
>    - Compatible with USB 3.0 and backwards compatible with USB 2.0
>    - Support Low speed (1.5 Mbps)/ Full speed (12 Mbps)/High speed (480
>    Mbps)/ Super speed (5 Gbps)
>    - Support auto switching between self-power and buspower mode
>