Materials that absorb RF energy

[Cornan]

10 minutes ago, Speedskater said:

Yes there's lots of talk, but no signs of due diligence.

 

Here is due diligence for you 

 

 

?

 

[Jud]

1 hour ago, jabbr said:

Very interesting all this talk about double shields over USB cables with various grounding strategies ... has anyone looked at/measured the RF output of a USB port? Do so-called “audiophile” PCs / streamers mitigate RF/EMI on the USB transmitter port? Are they spewing RF?

 

I am the king of gradually leading threads OT, so it's with a knowing smile I ask whether this can be discussed on one of the other threads devoted to it. 

[Cornan]

6 minutes ago, Jud said:

 

I am the king of gradually leading threads OT, so it's with a knowing smile I ask whether this can be discussed on one of the other threads devoted to it. 

 

It is all about reading behind the lines! ?

[jabbr]

1 hour ago, Jud said:

 

I am the king of gradually leading threads OT, so it's with a knowing smile I ask whether this can be discussed on one of the other threads devoted to it. 

I’m talking about the USB port itself as a potential source of RF/EMI ... Which thread? 

[Jud]

11 minutes ago, jabbr said:

I’m talking about the USB port itself as a potential source of RF/EMI ... Which thread? 

 

The multiple threads about double shields over USB cables.

[jabbr]

2 hours ago, Jud said:

 

The multiple threads about double shields over USB cables.

 

I’d be off topic because not discussing SQ related to types of shields.

[Jud]

5 hours ago, jabbr said:

 

I’d be off topic because not discussing SQ related to types of shields.

 

OK.   

[Ralf11]

part of a post on another thread by @jabbr copied here:

 

1 hour ago, jabbr said:

3) I do strongly suspect that audible differences between USB cables has to do with radiated vs conducted EMI including EMI radiated from the USB transmitters. This has to do with common vs differential mode noise. It is well known that shielding patterns affects radiated EMI (not just external EMI).

 

 

[Speedskater]

Shielded cables are not a big deal. No reason to mess up a cable design.

[jabbr]

16 hours ago, Ralf11 said:

part of a post on another thread by @jabbr copied here:

 

 

I’ve talked about this above but there is often a misunderstanding of the role of the “shield” as if the shield only exists to prevent external EMI from affecting the signal.

 

The “shield” is capacitatively coupled with the signal and forms a return path for radiated EMI ie common mode noise. That’s why the “shield”is connected to the source ground plane — the “shield” is an extension of the ground plane itself!

 

In this case however, the shield is not acting simply as a faraday cage nor absorbing RF, rather providing a return path for radiated ie common mode RF.

[jabbr]

3 hours ago, Speedskater said:

Shielded cables are not a big deal. No reason to mess up a cable design.

 

What are you trying to say? Different shields are used in different situations, that’s well known. What are you worried is going to be “messed up”?

[Speedskater]

3 hours ago, jabbr said:

 

What are you trying to say? Different shields are used in different situations, that’s well known. What are you worried is going to be “messed up”?

Incorrectly made boutique USB (and almost every other kind of analog and digital) interconnect cables.

[jabbr]

34 minutes ago, Speedskater said:

Incorrectly made boutique USB (and almost every other kind of analog and digital) interconnect cables.

 

We aren't discussing USB cable compliance testing nor cable QA, nor am I aware that the cable specification deals with common mode noise and radiated vs conducted EMI, for example, nor anything to do with this topic.

[Ralf11]

4 hours ago, jabbr said:

I’ve talked about this above but there is often a misunderstanding of the role of the “shield” as if the shield only exists to prevent external EMI from affecting the signal.

 

The “shield” is capacitatively coupled with the signal and forms a return path for radiated EMI ie common mode noise. That’s why the “shield”is connected to the source ground plane — the “shield” is an extension of the ground plane itself!

 

In this case however, the shield is not acting simply as a faraday cage nor absorbing RF, rather providing a return path for radiated ie common mode RF.

 

 

But, could a sheath of RAM (or a plane of it normal to a USB cable run, placed next to the DAC) reduce EMI?

[jabbr]

1 minute ago, Ralf11 said:

 

 

But, could a sheath of RAM (or a plane of it normal to a USB cable run, placed next to the DAC) reduce EMI?

 

It could reduce external EMI from being picked up by the cable i.e. a shield. If the RAM is conductive and is placed such that it capacitively couples to the USB lines and is connected to the ground at the USB source, then it can form a return path for EMI radiated from the USB port i.e. common mode noise.

 

try this: https://www.electronic.nu/en/2016/05/30/shielded-cables-their-role-in-reducing-emi-susceptibilty-and-emissions/

https://www.silabs.com/Marcom Documents/Resources/EMI-guide.pdf

[jabbr]

3 hours ago, Ralf11 said:

 

 

But, could a sheath of RAM (or a plane of it normal to a USB cable run, placed next to the DAC) reduce EMI?

Let me add : you need to consider where the EMI is coming from to determine how to shield or mitigate 

[Ralf11]

hot from the lab:

 

https://phys.org/news/2018-09-composite-significantly-electromagnetic-pollution.html?utm_source=menu&utm_medium=link&utm_campaign=item-menu

 

[Speedskater]

18 hours ago, Ralf11 said:

hot from the lab:

That's about microwave frequencies inside a chassis.

 

Not about audio components, neither analog or digital.

[Ralf11]

it's ok if you don't understand why basic research is relevant

[Speedskater]

1 hour ago, Ralf11 said:

it's ok if you don't understand why basic research is relevant

I understand that what's important at microwave frequencies and what's important at analog & digital audio frequencies are very different things indeed!

[Cornan]

1 hour ago, Speedskater said:

I understand that what's important at microwave frequencies and what's important at analog & digital audio frequencies are very different things indeed!

 

Let us know then!

[Ralf11]

1 hour ago, Speedskater said:

I understand that what's important at microwave frequencies and what's important at analog & digital audio frequencies are very different things indeed!

 

Do you understand that physical properties at microwave frequencies can be important at  digital audio frequencies??

 

 Do you understand that materials properties affecting microwave frequencies can be altered for lower frequencies??

 

 

[Ralf11]

On 8/11/2018 at 10:29 PM, Ralf11 said:

ok, my understanding is that they do not function well (or are not proven to) under certain conditions - not true?

 

 

 

ok Bill - it's fixed: 

 

https://phys.org/news/2019-12-maxwell-electromagnetism-smaller-scales.html