Ethernet to BNC, SMA or N - Page 1
Forum section: electronics / testgear

author: xymox
author_rank: Contributor
timestamp: September 14, 2020, 02:50:32 am
content: I need to hook a spectrum analyzer to Ethernet cables to test them. Like cat 8 and beyond. Its 4 pairs. 10khz - 3Ghz. Ideally what I need would be a test jig that that has impedance conversion for the 100Ohm to 75 or 50 ohm BNC or SMA or N. So Ethernet on one side, 4 connectors on the other. Cat 8 jack > PCB > Connectors.I have googled till im cross eyed.. I am not finding anything.

author: Yansi
author_rank: Super Contributor
timestamp: September 14, 2020, 07:17:11 am
content: Will probably require a custom design. RJ45 terminal (if required so), a wideband balun transformer and a suitable 50ohm connector (SMA?) to connect your analyzer.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 06:16:18 pm
content: Quote from: xymox on September 14, 2020, 02:50:32 amFirst hit:https://www.keysight.com/en/pd-2711221-pn-N5395C/ethernet-10-100-1g-transmitter-electrical-test-fixture-for-n5392b-c-10-100-1g-compliance-application?cc=US&lc=enghttps://teledynelecroy.com/options/productseries.aspx?mseries=252&groupid=140Not seeing the problem.

author: ogden
author_rank: Super Contributor
timestamp: September 14, 2020, 06:50:31 pm
content: 1000BASE-T test fixtures goes up-to 250Mhz at best. OP mentioned 10khz - 3Ghz, Cat8 bandwidth is 2GHz.

author: xymox
author_rank: Contributor
timestamp: September 14, 2020, 10:29:08 pm
content: Quote from: ogden on September 14, 2020, 06:50:31 pmInteresting.. Nice board..But yea.... I need to get to 2Ghz. I really dont need all that stuff on that board, cool and handy tho, but I need need passive, very wideband, channels.Yea, I know I can buy dedicated testers, but, I want to really do detailed very analog analysis..

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 10:59:26 pm
content: It's just the first Google hits. I had a look on Keysights site, saw the CAT 7 and some papers on 8. I just assumed you would contact them as it's obvious they are in the mix. I didn't search Teledynes site but assume they also are still developing fixtures. I would just pick up the phone and call them.There may be other companies. I didn't spend a lot of time looking.

author: xymox
author_rank: Contributor
timestamp: September 15, 2020, 05:29:00 pm
content: Well i was hoping for some cheap, quick easy solution. That was why I posted.. I was hoping someone might make a balan based BNC to Cat 8 to BNC box for some reason other then testing. Or maybe just a 1Ghz version.. TONS of people make 250Mhz versions. A 2Ghz version, with 4 lines thru one wire and really good shielding would be appealing for many applications. So I just had a hope someone already had one..Thank you tho.

author: ogden
author_rank: Super Contributor
timestamp: September 15, 2020, 05:36:38 pm
content: I doubt that you can find Cat8 testing fixtures for "affordable price" if I can say so. Keysight board could be good starting point for you to make your own. For S11, S21 measurements you need to build two boards, each with  and  parts in it. 3GHz balun could be challenging but interesting build provided you have VNA of said range. In case of success you could have some pocket business in result as well.

author: switchabl
author_rank: Frequent Contributor
timestamp: September 15, 2020, 05:54:46 pm
content: Keysight also has a 10GBase-T fixture available, which is specified to 3GHz. It may or may not be good enough for what you want to do.https://www.keysight.com/de/pd-1439887-pn-U7237A/10gbase-t-transmitter-electrical-test-fixturehttps://www.keysight.com/upload/cmc_upload/All/10GB-T_man.pdfThere are similar options from Lecroy and Tektronix.Whether you use one of those or make your own, you will likely have to put in quite a bit of work characterising the fixture so you can de-embed it from your measurements. Also, modern network analyzers usually have the option to combine two ports into a virtual differential one. That may be preferable to using baluns. Of course you need a VNA with at least 4 ports for that (and ideally 16 if you want to characterize all pairs at the same time).

author: ogden
author_rank: Super Contributor
timestamp: September 15, 2020, 06:07:34 pm
content: Precision Instruments 3GHz balun PI-102 alone costs $1090.95

author: switchabl
author_rank: Frequent Contributor
timestamp: September 15, 2020, 06:42:09 pm
content: Well, "affordable" very much depends on the context. If you are working on communication systems that require Cat. 8 cabling and cannot afford a balun, then the test fixture is probably the least of your problems.

author: ogden
author_rank: Super Contributor
timestamp: September 15, 2020, 07:26:27 pm
content: It's not even about "affordable"! OP wanted to find "cheap, quick and easy solution". In short: forgetit.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 15, 2020, 11:57:05 pm
content: Quote from: xymox on September 15, 2020, 05:29:00 pmNot sure what cheap would mean. But it would be easy enough to make the call to find out if they even offer anything. Then again, if it's for a home project and cheap is $50, I wouldn't bother them.

author: Brumby
author_rank: Unknown
timestamp: September 16, 2020, 12:17:56 am
content: Yeah .... I keep wondering what your definition of "cheap" is.What sort of budget were you looking at for this?

author: xymox
author_rank: Contributor
timestamp: September 20, 2020, 11:29:52 pm
content: Cheap.. hehehe... Well $1000 is out. $500 is unpleasant.. $250 would be OK. However you know with enough time something will pop out of China thats $20.. Free shipping..So my thinking was why i should spend $1000+ for something that will, or may already be, $20.I am not doing engineering or product development. I simply need to do some testing. Damn near a hobby. So a big expense will have no return on investment. I don't need and stds compliance. No traceability or calibration.I have already made up cable. Not even using a impeadance conversion. Tracking generator, normalization, this is already close.. Not ideal obviously but it works sorta.

author: ogden
author_rank: Super Contributor
timestamp: September 21, 2020, 04:41:49 pm
content: Quote from: xymox on September 20, 2020, 11:29:52 pmHere you go:https://www.aliexpress.com/wholesale?SearchText=Differential+Single-Ended+Converter+Balun. By replacing 3x capacitors with 3x 0ohm resistors and removing two traces for insanely stupid option to short(?) balanced end, you will seemingly get what you are looking for (cheap). Thou reaching promised 3GHz is questionable. Image ot thing attached.