Ethernet Cables - which are the most important?

[mansr]

Despite what people will tell you, as long as they provide a reliable connection, Ethernet cables make no difference whatsoever. Cat 5e is good for gigabit speeds over at least 100 feet. While there are cheap cables that don't quite meet the specs, Belkin is perfectly fine. Stick with them and spend your money where it matters, such as on music.

[mansr]

I suspect the power consumption of the Ethernet PHY within a streamer may vary to some degree depending on the quality of the differential signal waveform arriving at the receiver. The Ethernet PHY is a sophisticated block of logic capable of extracting the data payload from the incoming signal which may have signal integrity that's far from ideal, but the amount of switching activity within the PHY can depend on how clean the incoming waveform is.

 

Do you have anything better than a suspicion to support this idea? It would seem easier to design a PHY to always operate the same way rather than somehow adapt to signal quality.

[mansr]

Each PHY only powers it's transmit pair. This means the TX pair feeding the endpoint, be it streamer or client computer, is determined by the network switch.

 

Gigabit Ethernet actually sends and receives on all four pairs at the same time. Not that it matters for this discussion.

[mansr]

Ethernet PHY designs by definition must adapt to a certain range of incoming signal quality.

 

Far simpler to always assume the worst. No need to adapt to anything.

[mansr]

Ethernet PHY is usually part of an Ethernet controller chip, so a streamer board-level designer only gets to choose the brand/model of the Ethernet chip.

 

The PHY is usually a separate chip, actually.

 

I suppose a bad Ethernet chip choice can doom the streamer design, though streamers are essentially audio-dedicated single-board computers, so it's a bit hard for me to imagine a computer board designer badly botching the Ethernet subsystem design, though I suppose anything is possible in this crazy world.

 

I've seen many badly botched board layouts.

[mansr]

Though starting out kind of dubious about Ethernet cables making any difference to SQ, I did hear a Baaske Ethernet iso transformer make a clear audible difference to the noise level in my system with a "noise sniffer" type box in the circuit. My suspicion would be that it would be noise (leakage current?) rather than data transmission and reception integrity that might account for any real audible differences.

 

Are you aware that Ethernet always has a transformer at either end? These days they are usually integrated in the RJ45 jack. Nothing below a few MHz gets through these.

[mansr]

"Eppur si muove."

Yes, I am well aware of that, which is why, as I mentioned, I was dubious about the possibility that anything involving Ethernet cables would make any difference. However: When I said I had a "noise sniffer" type box in the circuit that made system noise audible, I mean *very* audible, nothing on the fringes of perception. And the Baaske transformer beyond any doubt considerably reduced the volume of this noise.

 

Were the Ethernet cables shielded?

[mansr]

I think that essentially all Ethernet cables are fine for data -- BJC probably allows a longer cable length but it's easy to measure packet dropout which should be zero (or near zero).

 

That doesn't mean that leakage currents aren't present. They certainly are. Sonic benefits of isolators go along with that. No nonsense. What is nonsense is solving a leakage current problem with a crazy expensive cable which, sorry, will only partially solve the problem at best.

 

 

Sent from my iPhone using Tapatalk

How much leakage current passes through an Ethernet transformer?

[mansr]

If I may answer a question with a question, any idea what was responsible for the audible noise reduction when inserting the Baaske transformer in my system?

 

 

Sent from my iPhone using Computer Audiophile

Without knowing what the Baaske device or your "noise sniffer" do, it's impossible to speculate.

[mansr]

Interesting information and exactly the nuggets I look for from you :~)

 

Do you know why the medical world uses Ethernet isolators like the Baaske units?

I looked it up: http://baaske-medical.de/isolation/ethernet-isolation/

 

It provides isolation up to 5 kV for protection of patients and equipment from voltage spikes should they somehow enter the network. In other words, it's a safety device.

[mansr]

I'm only looking for answers and trying to square information. It seems that arguments against expensive Ethernet cables go down the path that they are immune from noise by design, so I'm trying to figure out the need to use further isolators in different environments etc...

The medical isolators are not noise filters. They are safety devices to prevent electrocution in case a malfunction elsewhere sends a high voltage down the network cable. Under normal circumstances they perform no function, much like a fuse or a GFCI.

[mansr]

Belden Mediatwist is as good as you need regarding intrapair skew because the pairs are bonded. For Ethernet, this will show up in the eye plot. Regarding "audio", Belden means "analog audio", not Ethernet: The Strange World of Cat 5e and Cat 6

Intrapair skew can be a problem for high speeds over long distances. For gigabit over typical domestic distances any Cat 5e is plenty. No matter what the circumstances, if the link works reliably, the skew is within whatever limits the receiver tolerates, and reducing it further won't improve a thing.

[mansr]

Too much stuff to quote individual posts.

 

First off, Ethernet PHYs

I have worked in the semiconductor field for 33 years, during that time I have worked on over 50 PHYs for many different standards including many Ethernet PHYs. As a matter of fact there is a good probability that your computer has a PHY I worked on. I know a little bit about the subject.

 

Ethernet PHYs DO draw different amounts of current depending on the signal integrity of the signal being fed into the receiver. There is a LOT of both analog and digital circuitry trying to extract the bits out of that noisy piece of wire. When these circuits are running full bore (to extract bits from very noisy wires) they use a LOT of power. Part of my job has been to design power networks in the chip that can try and deliver clean power to those analog circuits. The advent of battery powered devices has put a premium on low power consumption of every chip in a device, so the PHYs are very carefully designed to use just the bare minimum of circuitry necessary to extract the bits. The result is the power varies radically with the signal integrity of the received signal.

 

When testing these PHYs we actually use a $700 cable to give the PHY the best signal integrity possible in order to find the baseline low power usage. These $700 cables use very expensive materials and extremely high precision geometry to have the least possible degradation on the signal. We then test with all kinds of more "normal" cables and lengths to see what happens in the real world.

 

What happens is that the BER stays almost the same, the chip is doing its job right and adjusting its internal circuitry to handle increasing signal degradation, which causes increased power draw and noise on power supplies and ground planes. At some point the BER skyrockets, it is interesting that what usually causes this is the PLLs that generate the timing for the PHY start outputing too much jitter as the noise on the PS and planes increases. One solution is to include an internal linear regulator on chip for the PLLs, which works, but increases the power dissipation of the chip. The customers don't like this.

 

The result of this modern heavy focus on power consumption HAS produced Ethernet PHYs which produce significantly varying power consumption depending on small changes in signal integrity.

 

On the issue of EMI coming from the cable to other parts of the system.

It is not so much the 125MHz symbol rate, but the PACKET rate that matters. In audio over Ethernet the packet rate frequently winds up right smack dab in the middle of the audio band where the human ear is quite sensitive. It is possible for the 125MHz to wind up getting into analog systems and going through non-linear parts of the circuit which can lead to small amounts of the packet frequency winding up in the audio signal. It probably is pretty low intensity and systems will vary radically on how sensitive they are to this, but I don't think it is wise to completely discount it.

 

On leakage currents and Ethernet cabling, I have no idea what is going on there. I have had no time to do any testing and won't for a long time. My lab is going to be packed up and in storage for many months so I won't be able to do any testing on this subject. I don't know enough about this subject at this time to make any comment on it.

 

On expensive Ethernet cables from audio cable makers, I'm fairly skeptical that they know what they are doing. I DO know what it takes to make a REALLY good cable, and what I have seen from the audio cable companies does not even come close to this. If these cables wind up sounding better I think it is much more likely to be an accident than any form of exceptional cable construction. And BTW making a cable with VERY low signal degradation DOES cost a lot of money, maybe the companies that make these should look into the audiophile market!

 

Someone asked the question about integrated PHYs, it's probably about 50/50 right now. A fair number of processors these days come with Ethernet MACs built in, so they just need a PHY on the outside. Other processors use a combo MAC/PHY chip. Then there are hybrid motherboards, the processor has a builtin MAC, so just a PHY is needed, but if the motherboard wants a second (or third) Ethernet port they use a combo chip. The motherboard of the computer I am typing on right now does this.

 

Well I guess that is about it for now.

 

John S.

Thanks for that. Now could you please clarify a couple of things?

 

1. How big a difference in PHY power draw would be expected between a regular Cat 5e cable and the best money can buy in a normal domestic environment?

 

2. How much do typical PHY power fluctuations actually affect the DAC circuitry in a competent design?

[mansr]

Here is some more on Ethernet PHYs and cable interactions.

 

One topic I did not cover in the first post is package, this can make a big difference. The package encapsulates the die and provides electrical connections that can be soldered onto a PC board. The "pads" on a die are way too small to be soldered onto normal PC boards and frequently made from a material that won't solder well.

 

As with everything else there are trade-offs here. Inexpensive packages have lots of inductance between the package pins and the die pads, on both the signal and power connections. This causes significant degradation in both signal integrity (SI) AND power integrity (PI). Expensive packages have vastly lower inductance for signals and have internal planes (just like on a PC board) for the power and ground. The have vastly lower SI and PI degradation, BUT they cost a LOT more. A cheap one might cost 12 cents and a really good one might cost 12 dollars. It is kind of hard to use a $12 package when the whole chip is earmarked to sell for $1.79

 

Here is a free tip, if you are a streamer or network DAC designer, go for your Ethernet chip in a BGA package. It will usually have vastly lower SI/PI degradation VS TQFP or QFN packages.

 

With a cheap package you can actually wind up with most of the SI/PI degradation happening in the last mm. There have been arguments along the lines "I'm only using 10 feet of Ethernet cable, how can that possibly put the PHY into a mode where it has to work much harder, 10 feet couldn't possibly add that much SI degradation". That is true, but this argument ignores the significant degradation that can be happening in the package. That alone can put the PHY past its "cruising along" mode into a working harder mode no matter what cable you use.

 

I worked on one program where the customer wanted very high performance but simply could not afford a good package, so they had to add multiple regulators on the die and live with the extra power consumption. Other customers have gone with higher cost packages so they don't have to deal with the higher complexity on the die. There are lots of different trade-offs being done.

 

This preoccupation with low power has produced chips which actually turn off most of the circuitry between packets, so every time a packet comes along the chip power draw may go from 2mA to 50mA and back when the packet is over. THIS can wreak havoc with power supply noise and in particular ground plane noise. Because this is happening at packet frequency not symbol frequency normal board decoupling schemes simply do not work at dealing with this.

 

One thing I hope you take away from this is that PHYs are very different from each other, something that might significantly affect one PHY may not affect another. Thus attempts to make things sound better in YOUR system may not work on someone elses or actually make it sound worse.

 

How cables interact with this can have interesting aspects. The chunks of hardware in the PHY are designed to deal with different types of distortion to the signal. Thus you can have the situation where one type of distortion causes a chunk of circuitry to be turned on that has significant affect on PG noise. Thus if a cable does something to decrease that particular distortion that chunk of circuitry may not be turned on. BUT frequently what it takes to decrease that distortion increases something else, but since the circuitry to deal with THAT distortion causes less noise, it is a win for that cable -- with THAT PHY. On a different PHY, it may make things worse.

 

I think this is happening in "audiophile" network cables. They try a bunch of different things that worked for analog cables or maybe S/PDIF cables and by accident wind up lowering one type of distortion that helps with a particular PHY, but winds up increasing a different type of distortion. Then they start throwing money at it (silver wire, special connectors etc etc.) which don't actually do much. So you wind up with a very expensive cable which does give some improvement with some equipment that uses the same PHY as they used in their tests. But on other systems it doesn't improve anything or makes it worse.

 

The best way to do it is to improve ALL aspects, not just one. This can be done but is expensive, but not in the way that I have seen from the audiophile cable makers.

 

John S.

It seems to me that rather than chasing after super-high signal quality at the input, it would be more effective to isolate the PHY from the rest of the circuit by means of a dedicated regulator and generous application of decoupling caps.

 

Also, would you agree that using silver instead of copper in otherwise identical cables will make no difference?

 

Finally, any opinion on directional Ethernet cables?