Bad BNC Cable or am I misunderstanding their specs? - Page 1
Forum section: electronics / beginners

author: windsmurf
author_rank: Frequent Contributor
timestamp: April 14, 2019, 08:43:47 pm
content: So I purchased five of what was described as "RG59/U 75ohm 50cm ( 19.1/2") BNC Male to BNC Male Coaxial Video Cable"I was planning on using them for short leads to a BNC to banana plugs, but I'm having issues with most them because resistance on the shielding connection is so high or totally open.So my question is, are these cables defective, or is the only thing the specs for a "Coaxial Video Cable" calls for is a good center connection, with high resistance or open on the shielding connection?The last picture is what I was expecting. That cable is from a different source, and cable itself is not RG59.

author: ataradov
author_rank: Super Contributor
timestamp: April 14, 2019, 09:08:55 pm
content: It is not clear from the pictures if your clips actually make a connection with the inner coaxial metal contact, not just rotating locking part. At leas in the first picture they are not, and that may explain the results.

author: tooki
author_rank: Super Contributor
timestamp: April 14, 2019, 09:12:33 pm
content: It looks to me as though you’re testing the bayonet shells, but not the actual mating surfaces for the shield. Those are the metal around the center dielectric.See the image onhttp://www.contrik.ch/en-ch/faqs/how-important-is-shielding-on-a-bnc-connector. Only the gold plated surfaces are the mating surfaces.See also these insulated BNCs, which are compatible with regular BNC. This illustrates what parts aren’t actually needed for the electrical connection:https://ec.staubli.com/products/includes/tm/hfline/bnc-sicherheits-steckverbinder_e.htm

author: David_AVD
author_rank: Super Contributor
timestamp: April 14, 2019, 09:18:32 pm
content: My guess is that those cables are junk. Where did you buy them?

author: windsmurf
author_rank: Frequent Contributor
timestamp: April 14, 2019, 09:48:23 pm
content: Quote from: tooki on April 14, 2019, 09:12:33 pmThank you for the connection information. I did probe the inside contacts using a needle probe but get the same results on the cables. When I actually do use the cables to two BNC/Banana connectors and measure known voltages, its way off, and voltages are moving all over the place, even with the cables sitting very still.The auction is here:https://www.ebay.com/itm/RG59-U-75ohm-50cm-19-1-2-BNC-Male-to-BNC-Male-Coaxial-Video-Cable/273561959972I thought about leaving negative feedback but had mixed feelings about doing that. Should one punish the seller for selling defective equipment unknowingly?...Or perhaps warn other buyers by leaving negative feedback as to the quality of his cables.... hmmm.....

author: ataradov
author_rank: Super Contributor
timestamp: April 14, 2019, 09:50:16 pm
content: Given the cost, it is no surprise really. You can't even get a decent BNC connector for anywhere close to $1.

author: windsmurf
author_rank: Frequent Contributor
timestamp: April 14, 2019, 10:04:39 pm
content: Quote from: ataradov on April 14, 2019, 09:50:16 pmHe seems to make profit with shipping, as shipping cost is 266% of the item price LOL

author: ataradov
author_rank: Super Contributor
timestamp: April 14, 2019, 10:07:12 pm
content: To be fair I have some of those cheap cables, and they do work reasonably well for general use. Would not use them for critical measurements, of course.So it is probably a matter of luck.You can pull down that plastic cover and see what is under it, it may be a simple fix. Nothing will fix the $1 price tag, of course, but it is possible to make them somewhat work.

author: ataradov
author_rank: Super Contributor
timestamp: April 14, 2019, 10:38:02 pm
content: See if the plastic is molded on. I just looked at my selection of the cables, and it looks like most of them have it molded on, so there is not much you can do. Other wise just pulling hard should do the trick.

author: windsmurf
author_rank: Frequent Contributor
timestamp: April 14, 2019, 10:47:46 pm
content: Quote from: ataradov on April 14, 2019, 10:38:02 pmI think its molded... doesn't budge. I guess I'll just return them. Thank you!

author: ataradov
author_rank: Super Contributor
timestamp: April 14, 2019, 10:49:12 pm
content: Is it even worth returning? You will pay more in shipping. And I'm sure if you talk to the seller, they will just refund our money.

author: windsmurf
author_rank: Frequent Contributor
timestamp: April 14, 2019, 11:23:43 pm
content: I sent a message to the seller yesterday about it but haven't heard anything back.The automatic EBay return system refunds all costs including shipping I paid originally, since the product was defective.I'm not sure if the return shipping costs me anything but when I tried it, it didn't go over any shipping costs, and automatically generated a prepaid return label.Not 100% sure if this gets deducted from the refund, but EBay didn't show me any cost for returning the item.I'm happy EBay is moving toward the industry trend of protecting the buyer rather than the seller.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 14, 2019, 11:39:09 pm
content: as ataradov said... returning may not worth the trouble and cost. sacrifice one cable, dissecting it may reveals where the problem is, china cheap crap sometime can be made china cheap good with a simple fix, usually worked for me. starting from pulling out that rubber cover of BNC end, either being pulled out, or being destroyed, cut with knife into pieces if necessary. i suspect the gnd wire only being pressed between the BNC connector and the rubber cover, rubber cover got lose, so did the wire. if no problem there, strip the whole rubber sheath to see whats really going on on the entire cable. sometime can be fun to see how to do cheap crap manufacturing process. ymmv.Quote from: windsmurf on April 14, 2019, 11:23:43 pmcorrect you will get 100% refunded incl shipping cost the item going to you, but your cost of returning it maybe burnt. so you'll lose both money and the cables. nothing to have fun with.