Author Topic: 🤪 Help with Crappy USB Isolator  (Read 587 times)

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Offline Lord of nothing

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🤪 Help with Crappy USB Isolator
« on: June 26, 2019, 09:18:22 pm »
Hi
I got this: https://www.delock.de/produkte/S_62982/merkmale.html
The claim to be perfect for better measurement Results and so on...  :-DD
Now I opened up:



Well the Case is just made out of Plastic with no shielding.  :box:
What kind of component are the Blue Flat thinks? And what is there purpose?
The Problem is there is power from the Laptop to the USB Device.
Are the Black "Box" the Power Transfert?
Sadly the Noise level are still the same so the idea is to desolder the think who transfer the power and use the Powerjack.
« Last Edit: June 26, 2019, 09:22:27 pm by Lord of nothing »
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Online wraper

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Re: 🤪 Help with Crappy USB Isolator
« Reply #1 on: June 26, 2019, 09:35:04 pm »
What kind of component are the Blue Flat thinks? And what is there purpose?
Those are ceramic capacitors.
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The Problem is there is power from the Laptop to the USB Device.
This is not a problem but how USB works. It seems this device can both supply power from computer or optional external PSU if higher current is required.
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Are the Black "Box" the Power Transfert?
This is isolated DC/DC converter.
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Sadly the Noise level are still the same so the idea is to desolder the think who transfer the power and use the Powerjack.
Is this noise level even related to USB? And what is the device to begin with? If it's cheap oscilloscope, you are unlikely to see any difference.
« Last Edit: June 26, 2019, 09:39:47 pm by wraper »
 
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Online Gyro

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Re: 🤪 Help with Crappy USB Isolator
« Reply #2 on: June 26, 2019, 09:43:43 pm »
An interesting implementation.  :-\

The "blue flat things" are a pair of Y caps, they appear to be in parallel, connecting the two USB grounds [EDIT: or at least shields] together. Unfortunately they will also couple high frequency ground noise.

Yes, the black box is an isolated DC-DC converter. Unfortunately, if you bypass it and use the DC jack (9-30V) it will still be using the on-board SMPS (U4) to power the isolates side. Noise level will depend on quality of design.

The 480Mbps claim is suspect. It looks as if they are using an ADUM4160 with the number ground off. If so, it is capable of USB2 Full speed (as they say in the description) but that is 12Mbps. It's USB2 High Speed is 480Mbps. I am not aware of any single chip USB High speed solutions at the moment.
« Last Edit: June 26, 2019, 09:45:55 pm by Gyro »
Chris

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Online wraper

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Re: 🤪 Help with Crappy USB Isolator
« Reply #3 on: June 26, 2019, 09:48:11 pm »
The "blue flat things" are a pair of Y caps, they appear to be in parallel, connecting the two USB grounds together. Unfortunately they will also couple high frequency ground noise.
Those are just usual 3kV rated capacitors, not Y safety capacitors. They might couple noise from computer but they also reduce noise from DC/DC converter. It does not seem they are connected in parallel. One of them is certainly coupling ground but other is not.
 
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Online Gyro

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Re: 🤪 Help with Crappy USB Isolator
« Reply #4 on: June 26, 2019, 09:53:51 pm »
The "blue flat things" are a pair of Y caps, they appear to be in parallel, connecting the two USB grounds together. Unfortunately they will also couple high frequency ground noise.
Those are just usual 3kV rated capacitors, not Y safety capacitors. They might couple noise from computer but they also reduce noise from DC/DC converter. It does not seem they are connected in parallel. One of them is certainly coupling ground but other is not.

Sure, I meant Y caps in the context of cheap high voltage isolation caps - Y caps are used in high volume, so cheap.

EDIT: I can see the marking on one of the caps now, yes, 3kV Z5U, no agency markings - I need to get my eyesight checked!  ::)

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It does not seem they are connected in parallel. One of them is certainly coupling ground but other is not.

Well spotted, I missed the isolated pads, possibly one coupling the 5V rails as well then.
« Last Edit: June 26, 2019, 09:59:29 pm by Gyro »
Chris

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Offline Lord of nothing

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Re: 🤪 Help with Crappy USB Isolator
« Reply #5 on: June 26, 2019, 09:56:27 pm »
THX for replay.
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If it's cheap oscilloscope, you are unlikely to see any difference.
Sorry I forgott to tell its an SDR. I see when my Laptop is connect to the "original" Lenovo Powersupply a lot of noise.
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Unfortunately they will also couple high frequency ground noise.
Is there an way to mod it to keep the noise away from the Laptop? Its from 2Mhz to at least 20Mhz (Range of my SDR with Up converter).
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Yes, the black box is an isolated DC-DC converter.
I guess on both sides are Coils?
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I am not aware of any single chip USB High speed solutions at the moment.
The SDR work with that. I dont know what the speed of the SDR is.
I just need a clean signal.
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Online wraper

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Re: 🤪 Help with Crappy USB Isolator
« Reply #6 on: June 26, 2019, 10:04:19 pm »
Try removing black DC/DC converter and both blue capacitors. However it's not guaranteed to provide any improvements. You also could try using USB cables with ferrite chokes if not using them already (note that some cheap cables have fake ferrite rings co them which are actually molded plastic with nothing inside). You also could just take some ferrite ring and making a few turns of USB cable through it.

« Last Edit: June 26, 2019, 10:11:27 pm by wraper »
 

Online Gyro

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Re: 🤪 Help with Crappy USB Isolator
« Reply #7 on: June 26, 2019, 10:07:05 pm »
Agreed, removing the Isolated DC-DC converter and two blue caps, might yield the quieter result. It depends though whether the DC-DC converter is noisier than the buck regulator for the external power jack or not.

Do a search for the ADuM4160 / ADUM3160 Eval board datasheet for a bit more info.
Chris

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Offline HB9EVI

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Re: 🤪 Help with Crappy USB Isolator
« Reply #8 on: June 27, 2019, 12:03:09 am »
Aside from the RF issues my guess is that it doesn't support hispeed usb (480mbps) - so no way to run SDR data over it; they are just not working with 12mbps only
easier to achieve is galvanic separation between antenna and SDR, at least if it's for reception only...
 

Offline magic

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Re: Help with Crappy USB Isolator
« Reply #9 on: June 27, 2019, 08:07:28 am »
OP's link does say
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Datentransferrate bis zu 480 Mbps
Perhaps it's :bullshit: though. Test it with a USB 2.0 pendrive, I ugess.

If you are already modding it, no problem with removing and bypassing the internal step-down converter. The external PSU will need to be exactly 5V then.

That's if the goal is noise. If it's about protection from lightning strikes to the antenna, it may be cheaper to use a sacrificial single board computer like RasPi to run the acquisition process and transfer captured data over WiFi. But I guess you have already bought that device, so...
 


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