Understanding and Troubleshooting Signal-to-Noise Ratio in Copper Testing

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So , as I mentioned , copper testing , the copper tester does a lot of things . This could be more specific . The certifier does a lot of things and one of the tests that it does is called a signal-to-noise ratio .

A lot of technicians don't understand what that is or how to do that , and I can explain it to you , but I figured it'd be much better if I brought on a subject matter expert . Of course you know I had to bring in Steve Cowles from AAM . Steve , how you doing my friend Good ?

The last 24 years I've been involved in the test equipment side of things Very cool , so we consider you a subject matter expert .

So when we're testing SNR , the higher the number the better . What it really boils down to what signal to noise ratio is , it's a little more complicated than just injecting the signal and measuring the relative noise that's influencing the cable . There's a lot more going on there . It's what we call channel operating margin testing .

So it takes into account the cabling performance characteristics . It takes into account the transceiver , the transmitter and receiver on both ends and it kind of weighs all that in when it's looking to that signal level and looking at the noise level . And IEEE sets out all the Ethernet standards .

They lay out everything , all the requirements for Ethernet and then of course the TIA and ANSI and ISO and everybody follows them for the performance standards for the cabling to support it . And IEEE specifies 10 to the minus 12 for your error rate . So that's a bit error rate , which means in one trillion bits of information . You're allowed one error , that's it .

One trillion bits , one trillion . You're only allowed one error bit in one trillion .

It's not what I would recommend , setting your tester to Pretty much . If you use 3 dB , you're good , especially at 10 gig . You want 3 dB of margin , or headroom , we like to call it . If you get to zero , it means you've got that one error in one trillion . That's what the zero means .

If you get below zero , you've got problems because then the transceivers can't overcome the errors with the auto correction and the modulation . So and you can get situations where you might be able to get 10 gig running on a cat 5e . If it's the only cable , if there's nothing else around it , there's no other things transmitting , you might be able to do it .

It's probably going to be for a shorter distance . You're probably not going to go all the way up to 100 meters with that , but you could probably run it . Now when you start introducing other things , you start to see problems . So if you've got legacy cable . This is where SNR testing really becomes handy .

If you've got a legacy system , you've got some 5e and you're getting ready to upgrade your network speeds , you know you were running one gate , now you want to run two and a half or you want to run five . You could do Certification testing just to make sure the cables still good , because time can have an impact on it .

But an SNR test gives you an idea how it's going to perform when you've got network you're up and running . So that's that's where an SNR test is going to come in handy . It goes beyond what certification does . Yeah , it it actually . You know it's more of a real-world scenario . I know I kind of went off on a tangent there , but you know that's right .

Let me know if I'm wrong with my , with my example here . So you know this about me . I have two dogs . I have a German Shepherd and a German Shepherd cattle dog mix . And Speaking of which , the cattle dog mix is right behind and he's got that typical cattle dog really high-pitched yelp . You know that the cattle dogs have .

So when we go to let the dogs out , they both go running to the back door . My , my , my shepherd . She knows to sit down and just kind of wait him . He can't control himself . He started doing a yippie-dee-peep , yippie-dee-peep , yippie-peep . Well , the other night Barbie and I were talking . As I was walking to the back door he started .

I couldn't hear Barbie because he was yippity-yippie , yippity . So if I was the transmitter and he was the noise , his noise level was too high that Barbie , the receiver , couldn't get my transmission signal . Is that a good example signal and noise ratio .

We , you know , crosstalk was , was one of the big test parameters and we we , those of us have been around for a while we know what crosstalk is . The old phone guys . Crosstalk was , you know , a voice line . You'd hear somebody else's conversation because it was two adjacent pairs and it would bleed over the same thing in the data world .

So that's within the cable between the pairs .

Now , when you get bundles of cables in an installation , now you've compounded that problem . You've got crosstalk not just within the cable that you have to to mitigate , but you've got crosstalk between cables that you have to mitigate .

And and as the cabling technology has advanced , the designs of the physical structure of the cable have overcome a lot of this , especially cat 6a .

I mean , if , if money's no object , I Would say you want to put cat 6a and no matter what you're doing , if you're doing copper twisted pair , you want to put cat 6a in , and especially if you're running PoE , but cat 6a will help mitigate that alien crosstalk . It helps mitigate , you know , the other noises that can get in other than the cable bundles .

You've got other noises , other interferers that can get into the cabling and shielding is another way to mitigate that issue too . You know , shielded cable will help with noise . Ingress and Outgress is that a word ?

You know so , so you know those . Those are some of the things that , when we start looking at the cabling like I mentioned that 5e earlier that's a perfect case where , yeah , maybe it's time to pull that cable out . If you need to run higher data rates , 5e is not going to cut it , if you know .

If , like I said , if you got a short run , it's just one run , you might be OK , but really you need to consider upgrading the cable if it's not going to support it .

If you get the 80 net cable adapter which comes with our K 60 , k , 61 , k , 71 series testers , that also does multi gig ethernet up to 10 gig SNR testing and it does P OE testing and you can do an auto test that will run all of that at once .

So it'll do a 10 , 10 gig , two and a half gig , five gig and it'll do a connection speed test at one and 100 meg and then it will do your P OE all at the same time and you can check or uncheck whatever you want . You know , if you're doing all of those it's a 43 second test .

It's not as fast as a cat , as a cat 6a test , which for us only takes six seconds . But you get a lot of information in that that 43 seconds with an SNR test and it's certainly way faster than running a BERT test . So if you're looking at doing the same thing , bert and SNR are , they're targeting the same problem .

So if you're having a cabling problem or you're trying to figure out if your cable is good enough to support specific speed , you come back to that error rate that I talked about . You know the one in a trillion . Both a BERT test and an SNR test are going after that same bit of information . They're trying to find out if I've got this errors .

If you have SNR within the IEEE limits , you can support that 10 to the minus 12 . And an SNR test at 43 seconds will give you that information . A BERT test capturing one bit in a trillion isn't really enough . You need to run that . Typically a BERT test will run that test about 100 times . And when you do that , because the amount of time it takes .

It takes like 1.7 minutes to run a BERT , just a single BERT to find out one in a trillion , because that's how long it takes you to send a trillion bits of information . We're talking at 10 gig . At the slower speeds it takes even longer .

So it takes you if you're going to run 100 of those , it's going to be almost 3 hours to do a BERT test to determine am I okay Versus an SNR test in 43 seconds . And really BERTs are really . They're a great test , but they're really more geared for lab .

There's a certain amount that we're allowed . If you have too much insertion loss , that signal degrades so much and then by the time it gets to that far end , the signal is so weak that now the noise is stronger than the signal . And that's when you run into SNR problems .

Insertion loss the most common cause of insertion loss , excessive insertion loss , is going to be the length of the cable . If your cable is too long , you're going to have bad insertion loss numbers . Now there's other ways to overcome that . There are some heavier gauge cables that have less insertion loss . Cat 6A is a good example .

It's typically a 23 gauge instead of a 24 like we have with 5E or 6 . So you're going to naturally because the copper has less resistance have less insertion loss that can impact you . And there are other things that can cause insertion loss .

You can get some insertion loss from poor termination I think we've talked about that one before , but anything that impacts crosstalk can impact your SNR values .

If you've got a poor termination at both ends , you're not only getting bad crosstalk between the pairs on the cable that's going to fail a certification test for crosstalk , but now that bad termination can potentially allow noise to ingress into the cable not egress ingress into that cable . So there's a lot of things that can impact this .

You can get a good result during your installation . If you're doing shielded cable and you don't do your bonding properly , that can cause problems . You can get external noise , not just alien crosstalk from other cables in a bundle .

If you don't ground and bond properly , you can actually turn your cable into an antenna and I think you've had this question in one of your More multiple times .

So that's gonna exclude your Maybe , like your fire alarm systems , your stuff that's operating at really low frequencies and stuff , but data cabling bond both ends to a ground .

Shielded patch cord is what ties into the equipment , the equipment's grounded . That's where your bond happens and it comes up a lot . And then people go what if I just use an unshielded patch cord ? No , you don't wanna use an unshielded patch cord . If you've got shielded cable you're gonna use a shielded patch cord .

That's the purpose is to help with that bond .

Then after that , if both of those are satisfied , then I'd be looking at maybe moisture somewhere , and if not moisture then maybe a mismatch of components Correct Like a 5E on a six , or maybe the mismatch of components might be higher up on the list actually , because that's more likely to happen than moisture does happen . So does heat .

So I think it would really be length , mismatch components , heat and then work .

I know you work for one of the best in your day job and there are some manufacturers out there that you know you get what you pay for and , yes , yes , you know like I think you did a comparison on one of your shows with cable from a big box store .

Now that I got my tester back , I need to do another show because at the time the cable that was being sold at Lowe's it's still one of the major manufacturers and that's not one of the better known major manufacturers , right ? So there's a lot of people who buy cable from like Amazon that have like some brand name that nobody's ever heard of .

That's what you need to test .

That's one of the times I'll find me a good , I'll find me a copper cat 5e , cat 6 , whatever off of Amazon and buy some and then compare that to One of the big three , one of the big four there .

Yes , if you're running PoE and you put that stuff in for PoE , you're gonna have problems because they have a really hard time Getting a good DC resistance on balance in that , so that you know that the pairs need to be within a certain tolerance of having the same resistance level and Copper-clad aluminum . It's a big problem out there .

It causes all kinds of issues for , for for cabling .

I mean a lot of issues . So okay , so attenuation is one . I guess what other things could cause signal , noises , ratio laws or failures .

This is like drilled in your head . You know Distance from electrical and crossing at 90 degrees and and . But you know , chuck , we see violations of that practice all the time in the field . Yes , I've seen people Testing cable with the cable tester laying on a transformer box . This is an installation part of it .

But the tester is sitting on an electrical transformer . It was there . It was convenient to place the tester there , not realizing the impact that that that electromagnetic interference plays .

Because if you're near an EMI source , not only can you have problems if you've got your tester sitting on a transform , but you've if you've got excessive EMI where your cables are running .

You know , maybe you've got a long run of of of Cat 5e or cat 6 , even 6a , and you've got a parallel run of electrical that runs for an extended distance Along it , you're gonna have problems , you're going to induce that noise into the cable .

If we have to cross electrical , cross it at a 90 . That's what it tells us . In real life it's not so black and white , it's shades of gray . You know , it really depends on what kind of a network you're running across at . Is it an analog phone line or is it a 10 gig network ?

That electrical cable is it a 20 amp circuit with nothing plugged into it , or is it a 20 amp circuit with 90 things plugged into it ? I mean , there's a lot of variables . So the 12 inches and 90 and cross it at 90 is to protect . So the .

The installers on the field don't have to think about those issues because if they follow that rule , they will be good for 95% of the installs they come across . So yeah , if you , if you have a cable sitting at 11.75 inches from electrical source , it probably will still work .

Yeah , there's just too many variables , but if you follow that rule , you're going to save yourself from getting lots of headaches down the path . That's the best way I can explain for EMI , because I get that question quite often , quite often .

Some of those kind of things are beyond the control of the low voltage installers because they came after the fact . Things happen . They put things in . They put a big subzero freezer with a big compressor on it right next to where the cabling runs through the tray . You're getting EMI .

But that's why we test and why we want headroom , because we don't know what's going to come after the fact . We test , we certify .

You want margin between the pass-fail limit line and where your cable actually performs , and that's why you do your job well , that's why you follow correct termination practices , that's why you cross it at 90 while you try to maintain that 12-inch distance , so that you've got as much buffer between where it could possibly fail and where you're actually performing as

possible , because you know something's going to happen down the road , something's going to change , somebody's going to do something to your cable . Somebody's going to install something right next to your cable . Anything could happen , yeah .

I can mount that hinged wall bracket to the wall with drywall anchors , because all I'm putting on is just a hinged wall bracket Today , right . What if they put PoE on that stuff in the future ? What if they mount a voicemail unit on that plywood ? Now , it's not install for tomorrow , that's right , yeah .

So once you break it down to your components , well , if the signal noise loss ratio is from attenuation , again go look at your cable length , look at your . You know , in hot area mismatch components . If it's crosstalk your avenues , there would be go to a shielded solution . Make sure your separations are good .

Does the signal , does the SNR test tell you the source ? Is really a RFI EMI issue or an attenuation issue ? How would you know which is which ?

We know those are always the worst combinations . Right , that's my worst performing pair . Let me go look at it . Look at my certification test and our tester . I think pretty much every tester has this . I saw one manufacturer a couple of weeks ago saying oh , we're the only ones that do this . Well , I think we all do it .

Where you have a TDR test as part of your , you know , to find the crosstalk or to find the return loss , there's a TDR trace in there . And when you look and say , okay , three and six is bad , let's look at my TDR trace for crosstalk and pinpoint where it is . Typically that's going to be one end of the other , but in some cases it could be a spike .

Maybe and this is why I'm an advocate of retesting cable periodically maybe your cable passed with flying colors when you installed it , but now you're six months down the road . You're having problems . You go in yep , snr looks horrible , let's run another certification test on that link .

Now we see a crosstalk spike halfway through the cable and what's happened is some other trade has come in . They say , oh , this cable trade looks convenient , I'm going to pull my whatever cable through here and I'm going to use zip ties and zip it to this bundle . And now they've crushed one of your cables and that's the culprit .

And you can see that on that crosstalk TDR and we're not the only ones that have that it's a great test . Now , it doesn't with our test I'm not sure about the others . With ours it doesn't add any time to the test , it's just part of the results . But I'm pretty sure most manufacturers have that TDR functionality built in for crosstalk and return loss .

We also add it for shield . So if you've installed shielded cabling and that might be an issue I've seen cases where a rodent chewed through the outer sheath and damaged the shield of the cable but didn't sever the conductors . And with a shield TDR locator you can pinpoint anomalies where maybe the shield's not totally compromised .

In a regular wire map test it looks good . You got that black line from S to S on your wire map . But that's not the whole story . So with the shield locator you see that TDR trace . You'll see a spike where that shield has been compromised but not totally severed .

. We are going to a global footprint . We were doing a Tech Talk every other week and it was just noon Eastern US time . We've gotten a lot of followers in other parts of the world Middle East and Europe and Asia Pacific and what we decided to do is go to once a month , but it's going to be three shows , one in each regional time segment , if you will .

So I'll be doing it at like 11 o'clock on Tuesday nights for the Asia Pacific team . I'll be doing it on Thursday mornings at 7 am for the Europe and Middle East , and then the US will be Thursdays at 3 pm . It will be one Thursday every month . The schedule is out on our website . If you go out there , go to aem-testcom , click the little .

I like to call it a hamburger , but it's only two lines , so you can't really call it a hamburger , but it's the upper right hand corner . You know what I'm talking about . You'll see a list of things that you can link to on the website . One of those is Tech Talk with Steve . You go there , it'll show you by region .

You pick which region you want and it'll show you the schedule in there . So we will be doing those . It'll essentially be the same show each of the three , especially this first one that I'm getting ready to do .

It's all going to be the same for each of the three shows but because we're going global , we may have different guests on in different regions , people that are well-known regionally rather than just well-known here in the US .

Other subject matter experts will also have some of my co-workers Jim Florio here in the US may host Werner Herron over in Dubai , or Al Sutherland in the UK may host , or Dixon Tan over in Singapore , so we could have other people hosting . We may even get our general manager , har Shang , on a couple of these shows , and Arvind are directly on the nearing .

So I've had Arvind on . In the past we did a Burt versus SNR comparison and he helped me understand the difference between the two quite a bit .

So the old style , what we call the legacy had a resistive touch display , and resistive touch displays have a whole different feel to them . The capacitive display is more like your cell phone , much more responsive to the fingertip .

The old version we would have a hard stylus that clipped into the back that you could use , because when you type on a keyboard for resistive it's much easier to do that than to try and use your finger . The new capacitive display you could use a soft stylus , but I've found just using my finger works great . Display is much brighter .

The new E-Series also now ships with CAD 8.1 permanent link adapters . So you get the CAD 8.1 channel , cad 8.1 permanent links . You can do CAD 8.1 and below . Of course , if you need to do CAD 8.2 , you're talking GG45 or Tera connectors We've got permanent link and channel adapters for those as well . Those are the big changes to the unit .

Functionally it's identical , uses the same firmware . It's the same tester . It's not a case where , oh , we're abandoning that old platform . That old platform is the same . They're both the same platform . It's the same exact tester . It's just a difference in that display .

In the new E-Series we've added some enhancements , like the permanent link when we get to the fiber testers . We now include the fiber inspection scope . In the E-Series we also include the adapter kit to do SCs . We always came with the ability to test LCs , but now we've included the SCs and then , beyond that , we also added OTDR .

This year so I think that was May we launched OTDR and the OTDR adapter can plug into your test pro so you can use it for troubleshooting or when you combine it with an optical loss test . With our fiber loss test system you now have tier two testing capability if you need it . The OTDR adapter also works in the NSA , our qualification plus tester .

It's the only qualifier on the market that you can plug an OTDR adapter into . And of course , the NSA was really designed for people doing move that changes network troubleshooting , network managers , network techs , those kind of people .

So having an OTDR in addition to being able to do a loopback fiber test with that , it really just adds a lot more functionality to the NSA as well .

So now that my test is calibrating ready , rock and roll .

Thanks for coming on again today and helping us solve the SNR debate and the issues that goes on with that , and maybe hopefully , some people learn some more from it .