Crimping for bnc connectors - coax - Page 1
Forum section: electronics / beginners

author: Moriambar
author_rank: Unknown
timestamp: December 07, 2020, 11:40:54 am
content: Hi,disclaimer: this has been a beginner mistake all along, please be nice!Some months ago I ordered on aliexpress some coax cable, since I'm going to buy new bits of equipment (counter/gpsldo) and I would've liked to crimp my own cables as I do with regular ones. I also bought some connectors, the crimping tool and so on. The cable is supposed to be RG58.Anyhow now I can't use the connectors because the conductor inside my cables is ~0.9mm of diameter and the "pointy" part of the connector that should go on it won't fit, since it's too small!My question is: is the cable or the connector bad? Where can I find something usable?Side-quest: are there any specific/best tools to cut (not strip but cut) the coax?Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 07, 2020, 11:54:16 am
content: The pin is too loose on the center conductor?Isn't it supposed to be? It gets crimped or soldered in place?I don't know what kind of connectors you have but presumably it's something like that....I'd say read the manual, but Ali specials, who knows.As for cutting, just ordinary diagonal cutters or shears are fine. It'll get crushed a bit at the end, but that doesn't matter after peeling it back for use.Tim

author: Moriambar
author_rank: Unknown
timestamp: December 07, 2020, 11:55:38 am
content: Quote from: T3sl4co1l on December 07, 2020, 11:54:16 amThe pin is too tight and the center conductor won't enter it, that's the problem so either the conductor is too large or I got ripped off with lousy pins, which are too small

author: Andy Watson
author_rank: Super Contributor
timestamp: December 07, 2020, 12:00:47 pm
content: Did you get 50\$\Omega\$ or 75\$\Omega\$ BNC ?

author: Moriambar
author_rank: Unknown
timestamp: December 07, 2020, 12:03:31 pm
content: Quote from: Andy Watson on December 07, 2020, 12:00:47 pmIt wasn't specified on the connectors, I'm afraid. The cable is 50\$\Omega\$

author: Renate
author_rank: Super Contributor
timestamp: December 07, 2020, 12:36:22 pm
content: https://labrigger.com/blog/2012/10/05/use-50-ohm-bncs-not-75-ohm/50 ohm have plastic inside, 75 ohm do not.I have found that for a specific cable there is only one specific connector and one specific crimper.Ok, that's the professional way if you have to make 10 to 10,000 cables."RG" names are not very specific (at least these days).

author: Moriambar
author_rank: Unknown
timestamp: December 07, 2020, 01:05:02 pm
content: they're 50\$\Omega\$ then

author: Renate
author_rank: Super Contributor
timestamp: December 07, 2020, 01:35:52 pm
content: Inner conductors can be of any size and also solid vs. stranded.You'll have to find the right connector.For production you definitely would want a crimper that ratchets and only releases when it's done.If you are knocking off a few cables for yourself a non-ratcheting crimper makes it easier to adjust for an inexact fit.Still, make sure that everything is crunched enough.

author: Moriambar
author_rank: Unknown
timestamp: December 07, 2020, 01:37:47 pm
content: Quote from: Renate on December 07, 2020, 01:35:52 pmThe problem is before the crimper in my case: the conductor (which is solid) does not fit into the connector pin. Thanks for the heads up anyway

author: madires
author_rank: Super Contributor
timestamp: December 07, 2020, 02:50:05 pm
content: There are different flavours of RG-58. RG-58 has a solid center conductor, while RG-58A/U and RG-58 C/U have stranded ones. The stranded core's diameter is usually around 0.9 to 0.95mm, and the solid core around 0.8mm. But RG-59 (75 Ohms) with a solid core has a smaller core diameter (0.6ish mm). My guess is that you got the wrong connectors, i.e. they are meant for RG-59.

author: Renate
author_rank: Super Contributor
timestamp: December 07, 2020, 04:11:00 pm
content: Quote from: Moriambar on December 07, 2020, 01:37:47 pmWell, yes, of course.I meant after you buy a different connector or a different cable or drill out the pin.

author: radiolistener
author_rank: Super Contributor
timestamp: December 07, 2020, 05:26:32 pm
content: Quote from: Renate on December 07, 2020, 12:36:22 pmthis is not an indicator. For example:This one is 75 Ohm BNC:And this one is 50 Ohm BNC:As you can see, both have plastic inside. Also there are BNC connectors that looks almost the same, but 75 Ohm version has a little thinner plastic core.Also Chinese coax cables may be 60 Ohm, if so it will works bad for both - for 50 and for 75 Ohm.

author: Benta
author_rank: Super Contributor
timestamp: December 07, 2020, 06:36:49 pm
content: Yep, I suspect 50/75 ohm mismatch as well. The 75 ohm centre pins are thinner and so is the centre conductor.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 07, 2020, 08:57:58 pm
content: Has anyone tried the Belden Double Bubble compression fittings???I see them advertised as "50 Ohm".Compression using a compression tool, not crimp, not clamp