Cable Specs For Oscilloscope - Page 1
Forum section: electronics / testgear

author: nathon
author_rank: Contributor
timestamp: December 13, 2013, 04:57:23 am
content: I'm purchasing some cable, connectors, adapters, etc for my bench. They'll be used with my oscilloscope and when I purchase the rest of my gear (function generator, new oscilloscope, etc.) it'll be used with that as well.My question is what type of coax should I use (e.g. RG-58, RG-59)? What terminators should I get? Is there anything else I should get besides T's, BNC to banana, and that type of thing?

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 13, 2013, 06:15:11 am
content: RG-58 has a characteristic impedance of 50 ohms, which normally matches most lab signal generators, but check yours. RG-59 has a characteristic impedance of 75 ohms. The only place I've seen it commonly used is in cable TV, TV antennas, and some FM broadcast radio antennas. Youprobablywant RG-58, but it really depends on the impedances of the things you are connecting with that coax.You should get some terminators that match the impedance of your coax and your signals. Probably that means 50 ohm assuming you're using RG-58, but it would mean 75 ohm if you know you need RG-59 for 75 ohm signal sources/loads.As far as what other kinds of adapters to get, it really depends on what you're doing. BNC female-to-female connectors can join two BNC cables together to make a longer cable. Male-to-male BNC lets you attach female BNC gadgets directly to your scope or signal generator. I routinely use BNC to PL-259/SO-239 adapters, mostly for ham radio type applications. I also need to go to and from male and female SMA connectors. And yes, banana plugs and jacks are always useful, both with male and female BNC connectors. If you're doing a lot of audio work, maybe RCA phone plug/jacks, or standard quarter-inch or eighth-inch phone plug/jacks might be something you'd see a lot of. You might want to break out stereo phone plugs to two separate BNCs.If you do a lot of RF work, a unidapt kit (google it) would be a very handy thing to have, to connect almost anything to almost anything else. They're expensive, but a collection of independent adapters can add up, too. I haven't bought one myself yet.For lower frequencies, I made a "this to that" box in an altoids tin, by just mounting one of every kind of connector I had in my junk box, plus a pair of banana jacks, and wiring them all in parallel. RCA, BNC, 1/8" audio, 1/4" audio, a few different coax power jacks. Not the most beautiful thing, and not impedance matched for RF, but it sees a lot of use.For a scope, I find myself using a standard 10X probe more than anything else, though. That loads a circuit less than a straight piece of coax, and it doesn't reflect the signal back as much.

author: notsob
author_rank: Frequent Contributor
timestamp: December 13, 2013, 06:25:54 am
content: It all depends on what you are measuring and what you are measuring it with, have a read of the coax wikihttp://en.wikipedia.org/wiki/Coaxial_cableinteresting to read the section "Choice of impedance" to see the historical reasons for selecting different impedance coaxand the comments column under "standards" to see where different types of coaxial cable are used.CheersPeteredit: for the average hobbyist it will most likely be 50 Ohm coax and fittings.

author: nathon
author_rank: Contributor
timestamp: December 13, 2013, 06:55:41 am
content: Thanks. Yea I knew about the impedance differences of those two types of coax, but not why you would choose one over the other with bench gear. Thanks for all the info! This helped a lot!

author: apelly
author_rank: Unknown
timestamp: December 13, 2013, 11:01:38 am
content: However.... What's a good trade-off between flexibility (softness, manageability), convenience, price, and signal integrity?Edit: I could look this up myself, but I already spend an two hours a day googling, and someone might know off the top of their head.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 13, 2013, 12:46:13 pm
content: Most signal generators & the like,have 50 Ohm output impedances,so RG58 50 Ohm coax cable is the most appropriate.20 years ago,if you bought RG59,you would most likely get real,fairly flexible 75 Ohm coax.Not any more!---what you will get is crap with a wispy aluminium shield,& a cruddy strip of Alfoil wrapped around it.RG59 is no longer a specification,so the scammers can sell anything!RG58 is still usually fairly good,with copper centre conductor & shield.---&it's flexible.

author: eV1Te
author_rank: Regular Contributor
timestamp: December 13, 2013, 01:20:05 pm
content: The most common cable is RG58 as already mentioned, but I also like RG174 a lot, it is more flexible and thinner than RG58 with the same 50 ohm impedance, but since it is thinner you have slightly higher loss of course, so for long distances at high frequency it might not be the best.RG58 is about 15 dB loss at 100 MHz for 100 meter cable.RG174 is about 24 dB for the same freq. and length.

author: Carrington
author_rank: Super Contributor
timestamp: December 13, 2013, 03:11:54 pm
content: Perhaps this could help you to choose:https://www.eevblog.com/forum/beginners/how-to-better-wire-the-bnc-connector-and-ghz-issue/I am also looking for good quality coax. cables.If you are looking cables for DMM, these are excellent. This seller has very good quality products.http://www.ebay.com/itm/170985687131

author: Macbeth
author_rank: Super Contributor
timestamp: December 13, 2013, 03:49:28 pm
content: Having just recently got my shiny new scope and sig gen (Hantek MSO5102D, Siglent SDG1025) I also needed to make some BNC patch cables.I used half meter lengths of RG6 (75 ohm), and cheap screw on BNC connectors (50 ohm). I only used RG6 because i've got 100 metres of the stuff on a reel I got ages ago to do DVB-S, DVB-T, and CCTV stuff around the house.It's quite stiff, but works well as a patch lead, tested up to my sig gen limit of 25 MHz. I don't think the 50/75 ohm difference matters on such a short length. It definitely works better than using two scope probes back to back. I was getting major attenuation at higher frequencies using that method. The scope probe only worked well on X10 and holding the spike tip into the centre of the sig gen BNC socket, with croc clip on the shield.If I had RG58 I would definitely have used that instead.

author: Frost
author_rank: Regular Contributor
timestamp: December 13, 2013, 05:23:43 pm
content: Quote from: Carrington on December 13, 2013, 03:11:54 pmI use the HFline series from Multi-Contact, they offer excellent build quality.The XLSS-58 are BNC test leads with two male connectors,they come in three different colors.http://www.multi-contact.com/products/hfline/1

author: Carrington
author_rank: Super Contributor
timestamp: December 13, 2013, 05:38:54 pm
content: Quote from: Frost on December 13, 2013, 05:23:43 pmThank you very much!They also have with RG174.Where did you buy it?

author: Frost
author_rank: Regular Contributor
timestamp: December 13, 2013, 06:13:03 pm
content: Quote from: Carrington on December 13, 2013, 05:38:54 pmYes, but the RG58 cables are also very flexible.The cable behaves more like a flexible test lead instead of a stiff coaxQuote from: Carrington on December 13, 2013, 05:38:54 pmThe Multi-Contact test leads normally at distrelec or voelkner.https://www.distrelec.de/home/enhttp://www.voelkner.de/(the shop page is only in german, but they deliver within the EU)

author: apelly
author_rank: Unknown
timestamp: December 13, 2013, 10:41:10 pm
content: Quote from: Carrington on December 13, 2013, 03:11:54 pmAnother epic thread.Interesting link uncovered there about RG-174:http://www.dxing.info/equipment/rg_174_coax_bryant.dx

author: Co6aka
author_rank: Unknown
timestamp: December 15, 2013, 11:58:24 pm
content: In the past, for RF, I've usually used RG-142 and the stranded-center-conductor variant for interconnects. A while back I acquired a generous supply of some funky similar-size ("RG-58 size") foil and braid shielded 6GHZ-rated cable, which is what I'm now using. Along this line, LMR-Ultraflex is should be an easily obtainable similar type cable... For RG-58-size, so yous could use da RG-58 connectaz, try this:http://www.timesmicrowave.com/downloads/products/LMR-195-UF.pdfAlso, keep in mind that roughly over 1GHz the Wong-Hung-Lo kwality make-China gold-kolor connectors don't look too pretty, so choose your hardware accordingly.