Custom RF cabling questions - Page 1
Forum section: electronics / general

author: purplxed
author_rank: Newbie
timestamp: December 25, 2024, 10:54:53 pm
content: Hello voltnuts!I've been lurking here for a bit and have started to develop a interest in metrology (ok, ok, that's a lie I was already interested, this forum just made me feel better about spending money on that interest). One thing I'm struggling with, though, is cabling. I prefer to make my own cables where I can, but I'm very unfamiliar with good brands around RF/coax cabling and connectors. Are there common brands everyone knows just work every time?I'm looking for suggestions on:Cable ManufacturersConnectors/Crimp EndsCrimpersATM I'm mostly looking to make my own cabling for GPSDOs and the 10 Mhz links to the lab equipment (so RG58/RG8 + N/TNC/BNC/SM{A,B}), with an eye toward expanding toward higher-frequency stuff in the future (looking into getting HAM licenses).I'm not allergic to spending a good money for quality parts and tools (particularly tools!), and if it helps I am in the USA atm, but willing to order stuff internationally.Thanks in advance for the knowledge!

author: TimFox
author_rank: Super Contributor
timestamp: December 25, 2024, 11:30:08 pm
content: Before and after retirement, I have used cable assemblies from Pasternack.Not cheap but good, and they have lots of variations.https://www.pasternack.com/nsearch.aspx?Category=Cable+Assemblies&sort=y&view_type=grid

author: tooki
author_rank: Super Contributor
timestamp: December 25, 2024, 11:53:55 pm
content: Cable:-Huber+Suhner-Belden-Times MicrowaveConnectors:-Huber+Suhner-Cinch/Johnson-Pasternack-Telegärtner-All the big connector companies (Amphenol, Molex, TE, Samtec, etc)Tools:-original manufacturer tools are awesome but $$$$$$-Daniels (DMC) and Astro Tools, who supply many of the OEM tools, but a bit cheaper direct-Knipex is a great compromise, with quality that leaves little to be desired-I haven’t tried them, but I suspect the stuff from Klein Tools and Greenlee/Tempo/Paladin Tools are more than adequateNothing you list is particularly demanding (not like, say, 6GHz+ microwave), so any decent brand of connectors and cable should be good enough. But you’ll definitely find that you like some designs better than others. I HIGHLY suggest carefully examining not only the drawings of connectors of interest, but also the assembly instructions. Some connectors are much easier to assemble than others.For example, for one project we had a bunch of MMCX connectors to terminate onto RG-196 cable (that’s the all-Teflon version of RG-178, basically). The ones from one of the expensive brands (probably Huber+Suhner, but I’m not sure anymore), but require a much more difficult assembly process because the shield is actually kept longer than the dielectric so it can fold back over the ferrule, meaning that you had to strip the jacket without fraying the shield even a bit, so that you can then slip on the inner crimp ferrule, then spread the shield back over the inner ferrule, and only then (without mangling the folded back shield too much) proceed to strip the dielectric and solder on the contact, before finally slipping over the connector body with outer ferrule and crimping it on.In contrast, the MMCX from Molex use a classic coax strip that is much easier to assemble. All the strip steps are done up front. No folding back, no inner ferrule, just strip everything up front, slip over the outer ferrule, solder on the pin, slip the shield over the crimp body of the connector body, slip down the ferrule and crimp. (I don’t know whether that sounds easier or not, but it certainly is in practice!) Most connectors work this way.In addition to ease of assembly, the other reason for studying the drawings and assembly instructions for the various connectors of interest is to try and settle on one or two ferrule crimp sizes. For example, the vast majority of connectors for RG-174, 316 and similar use a 3.25mm hex crimp for the ferrule. But there are a few exceptions, I think I saw some that need 3.7mm or something. If you can standardize on one or two sizes, you’ll minimize tooling expense. I think this is much less of a challenge for the larger diameter coaxes like the RG-58 and RG-8 that you mentioned — the smaller cables (RG-178, RG-196, etc) tend to have more crimp size variation.The more common crimp sizes are also what are easier to find. Oddball sizes may leave you with no alternatives to the super-expensive tools. For example, the 2.67mm hex crimp needed by some of the RG-178/196 MMCX connectors is not available on any Knipex die, while the 3.25mm is.A little tip for the smaller cables like the 178: when buying connectors, look carefully at the ferrule shape. Top-quality connectors have the crimp barrel and ferrule inner diameters tailored to the cable. Cheaper ones reuse the crimp barrel from the RG-174-type connectors, and just use a reducing crimp ferrule with a narrowed entry hole for strain relief. These will have a slight impedance discontinuity at the crimp, because the dielectric suddenly has an air gap around it. I’m sure they’re OK for many applications, but it’s really a bit of a kludge and certainly undesirable for demanding things. My old boss (an RF expert who likes to say “everything under 3GHz is DC to me!”) thinks they’re garbage.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 26, 2024, 08:57:08 am
content: HelloFirst try to define what type of connector , N , SMA ... micro and nano connector are an other concern.There is a lot of surplus used / NOS cables on Ebay and other website far cheaper than newRegardsOS

author: purplxed
author_rank: Newbie
timestamp: December 30, 2024, 01:09:17 am
content: Thanks for the replies everyone, will be using this information over the next week to order some new gear!