RG-58 cable with solid core vs stranded, does it matter much ? - Page 1
Forum section: electronics / beginners

author: BravoV
author_rank: Super Contributor
timestamp: March 27, 2014, 04:32:27 am
content: To be specific, the length I'm talking about here are only 0.5 up to 2 meters max (6.5 ft), that to be used specifically between test & measurement equipments like scope, fg, pulse-gen and etc.Working signal frequency is not too ambitious, only < 500 Mhz.I don't care if the the solid core one is stiffer than the one with stranded wires which is obvious.My concern is signal integrity & quality, and the most important is the consistency since these cables will be used on the bench which will be moved a lot, or abused like accidentally over bentand etc than a statically installed one.Also certain coax has the aluminium foil (example photo below) wrapping around the copper braided shield, is this type "significantly" better than the one without the foil ?Btw, I'm only interested in making my own cable, and not interested at those pre-made, branded expensive ones.Thanks in advance.Edit : Below is wrong photo since it has aluminium braid, it was randomly grabbed from Google.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 27, 2014, 05:13:42 am
content: Bench use, go stranded and, if you feel it's necessary, foil is great too. Although if it's got foil, I believe it's not technically RG-58 anymore.At high frequencies (over 100MHz or so), the roughness of the braid becomes substantial, resulting in rather high losses. It's also notoriously leaky stuff.But yeah, almost anything is better than RG-58.RG-8 or thereabouts is the good stuff, used for CATV distribution and whatnot. It's a bit heavy for BNCs though (not to mention 75 ohm; there's a 50 ohm version too, somewhere..?).Tim

author: vk6zgo
author_rank: Super Contributor
timestamp: March 27, 2014, 06:27:55 am
content: Quote from: BravoV on March 27, 2014, 04:32:27 amFrom your picture,the braid is also aluminium,which means that it is virtually impossible to solder.This may not be a problem right now,but what may be,is that crimp connectors for RG58 are designed for the real stuff (stranded core,& copper braid),& probably won't fit.I would suggest that what you have is what is sold widely as "RG59"--which it isn't,either!The "RG" series of cables are no longer regarded as a specification,& there is a lot of mislabelled "El Cheapo"stuff out thereProducing the same crappy cable & labelling it "RG58" "RG59","RG8x" or whatever is not beyond these folk.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 27, 2014, 09:47:57 am
content: Um, I would expect that's tinned copper. Now, if it *is* aluminum braid, eww...Tim

author: BravoV
author_rank: Super Contributor
timestamp: March 27, 2014, 10:01:15 am
content: Quote from: T3sl4co1l on March 27, 2014, 05:13:42 amTim, mind elaborate further on the foil part ? Also the loses at high freq, say like <= 300 Mhz ? Even say like only one or two feet long ?Quote from: T3sl4co1l on March 27, 2014, 05:13:42 amUnfortunately, only RG-58, the RG-8 is way too thick and too stiff at the bench, I tried it at my friend's bench, way too bulky and I'm willing to compromise with RG-58.@vk6zgoSorry, wrong picture, it was randomly grabbed from Google and apparently I missed that detail.No way I'm going to buy that cable, both core and the shield must be made from copper.

author: VK5RC
author_rank: Unknown
timestamp: March 27, 2014, 10:42:34 am
content: What about LMR 240 flexible, its pretty close to RG 8 level loss, only little stiffer than RG 58, same diameter?What connectors are you planning to use?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 27, 2014, 11:55:58 am
content: Foil -- the smooth surface means AC works better.It's more, well, coaxial!I guess experience counts; for instance, I can set up a pulse generator with a length of RG-174 (as pulse forming network) and observe the dispersion due to losses, even of just a few feet (impaired rise time, poor settling). You'll see the same effects on real RG-58, a little less exaggerated (since RG-174 is *lossy* -- basically, thinner RG-58 with a stranded core), but nonetheless just as significant over proportionally longer lengths.Going up to 300MHz, over a couple feet length, I think would be around where things become dubious. So, it's up to you at that point; suck it and see, etc.For most purposes, a couple feet of the stuff should be fine (say 6' / 2m cables). Precision RF or fast pulse work, better done with better cable. Anything under 50MHz, who cares. If you're doing a lot of these kinds of things, it would be worth keeping some quality cables on hand -- to check and compare, if nothing else. (Always suspect your instruments and connections?)Tim

author: BravoV
author_rank: Super Contributor
timestamp: March 27, 2014, 07:21:35 pm
content: Quote from: VK5RC on March 27, 2014, 10:42:34 amAll will be using BNC.LMR 240, interesting, it has the OD of 6.1 mm, while RG-58 is 5.0 mm, will it fit at standard BNC connector ?

author: VK5RC
author_rank: Unknown
timestamp: March 27, 2014, 07:49:31 pm
content: I am not sure re LMR fitting standard RG 58 connectors, I hadn't picked the diameter difference in use here, for a interconnect cable to a moveable 400MHz antenna (here I am using Times' specific connectors but they are N type not BNC).The connectors I would make sure you get good quality ones, as I have had trouble with connectors I bought cheaply having a high reflectivity/high SWR, it took me quite a while to twig what was going on as the DC testing (with DMM) was fine.

author: linux-works
author_rank: Super Contributor
timestamp: March 27, 2014, 09:27:15 pm
content: what I am told, at least in terms of audio cables, is that the foil wrap is more effective at higher freqs and the braid wrap is better for lower freqs.I would want both. no harm in getting both.btw, there are (apparently) both 50ohm and 75ohm bnc's; most are 50ohm but you might as well be sure if you are buying new parts.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 28, 2014, 01:19:01 am
content: It isn't always quite as easy to determine.The old 75 Ohm "TV antenna cable" with very wispy braid,& a length of aluminium foil fairly loosely twisted around it is terrible stuff to work with,but is considerably lower loss thanrealRG59,when it gets above a couple of hundred MHz.This is from actual testing on a TV RF distribution system---we ran out of the normal coax,& had to use RG59 for a temporary run during a Telethon at TVW7 Studio.The only specs I can find on the Internet are for the real stuff,but I sorely doubt if the "pretend" RG59 is any better!"Quad shield" RG6 is only a little bit better than RG59 from its specs,so there is a lot more to losses than just shielding,such as type of dielectric.The "old" TV cable had a substantially air dielectric,which accounted for its low loss,& also its fragility.RG6 has become the standard for home terrestrial TV antennas despite originally being designed for cable TV use,where the shielding to meet specs re leakage & ingress of signals were more important than loss figures.RG6 is mechanically superior,to any other cable used previously in this service.People accept its higher losses,as the cable runs in a house are quite short,(compared to a TV Studio),so most times there is plenty of signal to work with.Remember,cable losses are specified as per 100ft/30m,so the actual loss with a normal tesl cable used in your lab will be very much less.

author: BravoV
author_rank: Super Contributor
timestamp: March 28, 2014, 05:14:17 pm
content: Thanks for replies !I concluded just few feet won't matter much, too much nit-picking.

author: JackOfVA
author_rank: Unknown
timestamp: March 28, 2014, 10:19:17 pm
content: I use RG-223 double shielded silver plated braid, stranded center conductor for test cables. About the same physical size as RG-58 but with much lower leakage.There are some real crappy cable assemblies and cable out of China labeled as RG-58, but with close to no braid coverage and who knows what impedance.I looked in detail at some DigiWave RG-58 cable a friend sent me to evaluate - details are on my web site at the link below, but the summary is that DigiWave must be the low cost subsidiary of One Hung Low manufacturing.http://www.cliftonlaboratories.com/the_curious_case_of.htm

author: dave_k
author_rank: Frequent Contributor
timestamp: March 29, 2014, 09:09:45 am
content: Quote from: BravoV on March 27, 2014, 07:21:35 pmRG-58 connectors won't fit on LMR-240 cable - the diameter of the inner conductor is 1.42mm compared with 0.8m for RG58.Connectors for LMR-240 are easy enough to find online.There is even a flexible version which is designated LMR-240-UF; might be better suited for lab hookup cables.

author: GreyWoolfe
author_rank: Unknown
timestamp: March 29, 2014, 11:56:05 am
content: Seek out Amphenol connectors. I have used cheap Wun Hung Lo connectors as a Ham it didn't take long to learn. Amphenol connectors are very high quality and worth every penny you'll spend.

author: ConKbot
author_rank: Super Contributor
timestamp: March 29, 2014, 05:52:51 pm
content: Quote from: dave_k on March 29, 2014, 09:09:45 amLMR-195 or LMR-195-UF is an option, and it is compatible with RG-58 BNC connectors. But +1 to grey woolfe, dont get cheap BNC's they dont hold up and dont go together nicely. Amphenol, Kings, Emerson, or any other big connector mfg would be preferred.

author: amiq
author_rank: Regular Contributor
timestamp: March 29, 2014, 09:03:21 pm
content: Quote from: JackOfVA on March 28, 2014, 10:19:17 pmI've been looking for stranded core RG223 type cable (I imagine it's quite a bit cheaper than RG400) - who makes it?

author: JackOfVA
author_rank: Unknown
timestamp: March 29, 2014, 10:19:25 pm
content: Quote from: amiq on March 29, 2014, 09:03:21 pmDon't think it exists - RG400 is, as you say, on the pricey side and the PTFE insulation makes it far too stiff for easy use in the lab environment. RG142 is similar to RG400, double shielded, PTFE insulation and jacket. It's available at US$ 2.85/ft from The RF Supplier in China.http://www.rfsupplier.com/coaxial-cable-m1760-rg142-feet-p-184.htmlI buy cable from them as well as some cable and connector assemblies I have made. The only problem I've had with their products is - and I think it's not unique to them, it's more a general Chinese thing - is that BNC connectors seem to be manufactured to the "nearest standard metric size" in some dimensions so that they do not perfectly fit a real mating BNC. Their SMA connectors and SMA cable assemblies are fine. My uses are in the HF and lower range, so their stuff may fall to pieces at UHF or microwave frequencies.

author: dave_k
author_rank: Frequent Contributor
timestamp: March 29, 2014, 10:25:25 pm
content: Quote from: ConKbot on March 29, 2014, 05:52:51 pmHuber+Suhner is my preferred connector brand for RF

author: apelly
author_rank: Unknown
timestamp: March 29, 2014, 11:19:10 pm
content: There are at least two good threads about different home built coax cables here. Damned if I can find them now though, sorry. To be fair, you probably have them bookmarked anyway.Thinking out loud... There was at least one good option for 50ohm thin & flexible cable. Again; damned if I can remember. I seem to recall someone doing extended runs of it for radio? There was an external link where some joker had done some fairly extensive testing on it. Can't remember frequencies though.Rereading; this is probably the most useless post ever!Oh well. Perhaps it will jog someones memory... I'd like to find them again anyway...

author: amiq
author_rank: Regular Contributor
timestamp: March 30, 2014, 07:13:48 am
content: To answer my own Q Huber + Suhner make stranded core RG223http://www.koax24.de/en/coaxial-cable/overview-50-o/49-61-mm-gr4/rg223.html.

author: BravoV
author_rank: Super Contributor
timestamp: March 30, 2014, 07:34:50 am
content: Quote from: ConKbot on March 29, 2014, 05:52:51 pmThanks, just downloaded the datasheet, looks like we have a winner here for BNC based bench cable, especially for the "UF" type. Attenuation @450 Mhz is 30.4dB/100meter or 9.3dB/100ft.Problem now is finding vendor who sell this locally which I doubt about it.Does anyone have any spare this cable type ? I need only less than 10 meters. ... <wishful thinking>