labflex 200 connector (26.5+ GHz for 0.195 shield) problem (high spec rg400?) - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: July 03, 2022, 10:43:25 am
content: So I want to repair a broke lab flex cable connector (it fell with an antenna tripod and got jammed so the nut wont turn). I cut off the connector but I realized a problemIt looks like a RG cable with higher rating. The shield diameter is 0.195, which is the same as rg400, but the problem is if you try to search, only 18GHz cables come up. What do I search for to get a connector compatible to 0.195 shield but with the better frequency rating?or maybe it was just a 18GHz connector that was rated for 31GHz as a cable. Is there such a SMA connector at 0.195 barrel, or is this don quixote ?

author: coppercone2
author_rank: Super Contributor
timestamp: July 04, 2022, 06:25:06 am
content: looks like its 18GHz connector, they don't sell a higher rated finished cable of the same type. No need for higher frequency, I just wanted to make sure I keep it within specification.

author: max-bit
author_rank: Frequent Contributor
timestamp: July 10, 2022, 08:29:38 pm
content: If the cable was specified for 26.5 GHz, then there must be connectors for 26.5 GHz (what were the connectors?)Upload photos?

author: coppercone2
author_rank: Super Contributor
timestamp: July 10, 2022, 08:59:28 pm
content: nah the cable is specified for 31 but the cable assembly from manufacturer is 18GHzmaybe you can get higher with a different connector but they don't sell 3.5mm for more then 18ghz on that cable size. Maybe 2.9 or apc has a connector for that, but I just wanted it the way it was before failure

author: coppercone2
author_rank: Super Contributor
timestamp: July 11, 2022, 11:05:55 pm
content: wow this cable is really weird, the dielectric is what looks to be tightly wound plumbers tape. I guess it aids in flex, but wow. Its braid over aluminized mylar over what looks like used car lot ribbons over packed teflon tape over a solid wire. Feels SO dodgy to work on.I think you can make DIY hardline cable by winding plumber tape over a wire and wrapping it with copper tape or stuffing it in the right diameter plumbing lol, my work bench looks like it got TPed

author: coppercone2
author_rank: Super Contributor
timestamp: July 14, 2022, 02:40:51 am
content: I wonder if you can do an Apollo 13 repair with teflon tape to repair a microwave link cable with minimal tools.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 14, 2022, 10:59:31 am
content: Quote from: coppercone2 on July 11, 2022, 11:05:55 pmI believe that kind of dielectric is not super uncommon in highly flexible cables. It is always all a tradeoff between loss, flexibility, repeatability, and cost. Using precision wrapped cores like that could result in a much more flexible cable since they can slide over eachother a bit. Usually during cable design, they take care that the distance between the different wraps is much smaller than the wavelegnth, because otherwise you can get strange notches in the frequency response of the cable. Same is true for wrapped outer conductors using silver-plated foils. They have to control the force during wrapping and the pitch very well to ensure good cable performance. Very high frequency cables tend to start putting the foil wrap length wise, so you put multiple pieces of foil in the length of the cable, and then wrap it with the outer braid to keep it in place. Gives lower loss, higher frequency performance, but at the cost of flexibility and bending life.Just because it is made that way does not mean it is easy to repair. After all, you can think of coaxial cables as a conductive rod with non-coductive wrapping and then some more conductor. Doesn't mean you can make a 30 GHz coaxial cable with some gardening tools though.As to the reason why they don't have higher frequency 3.5 mm connectors available for that cable: They usually have a limited set of connector types with specific outer diameters. It might not be make financial sense to make a custom version of a high-frequency 3.5 mm connector for this specific outer diameter, and instead just switch to 2.92 mm instead (which they might also be able to use on other cables that go to say 40 GHz).Gore, H+S, Amphenol, etc all sell cables with connectors that cannot reach the maximum specified frequency of the cable. EG, Gore 50 GHz phaseflex with 3.5 mm or 2.92 mm connectors, H+S Sucoflex 102 (rated to 46 GHz iirc) with N connectors, etc etc.It's simply easier to design a cable that is good to 50 GHz, and use it for a number of assemblies from 10->50 GHz, than make a specific cable for each type. Coaxial extrusion dies for these kinds of applications can run in to the tens or even hundreds of thousands of euros to manufacture.

author: coppercone2
author_rank: Super Contributor
timestamp: July 14, 2022, 11:18:34 am
content: hmm, regardless it seems like it might be interesting to try to make a wrapped coaxial cable. Yes, I do think the strips are length wise because it does not unravel well.

author: max-bit
author_rank: Frequent Contributor
timestamp: July 14, 2022, 11:47:26 am
content: When making cables for such high frequencies, precision is needed, and precision means using the right tools. Connectors for such high frequency are earned with appropriate tools and then measured on VNA. You can earn such connectors at home (2.92mm 1.85mm etc), but you will not know its parameters. The question is, what do you use it for, if for the measurements such a cable becomes a puzzle to some extent. But if you measure in such high frequencies, you should have access to VNA ~ 50 GHzPSRG40x cables are connection cables, not measurement cables. Combine well - forget it.

author: coppercone2
author_rank: Super Contributor
timestamp: July 14, 2022, 03:43:36 pm
content: I only have up to 20GHz at the moment, if the connectors were no so expensive I would try to mess around. If I ever need to shorten these cables I might try it

author: coppercone2
author_rank: Super Contributor
timestamp: July 15, 2022, 01:27:02 pm
content: How important is the termination on this cable? I see that this connector has a step to it, so you need to strip the outer shield to a certain distance then strip the inner shield . But there is a metalized Mylar ribbon inside the cable between the inner and outer braid, thats a bit difficult to trim properly so that it sits right under the outer shield. it seems that the braid gets a bit ruffled when sliding on the connectorIs this ribbon important to have millimeter cutting precision? I would love to do experiments if it was not 60$ a connectorAnyone feel like their dealing with the stones from the fifth element here?

author: coppercone2
author_rank: Super Contributor
timestamp: July 16, 2022, 01:41:03 am
content: well, its not necessary that this repair need to occur at the highest frequencies, I wonder what performance you can get from a roll of teflon tape to fix a slightly too short coaxial cable. I think experiments can be done with cheap BNC connectors.Not sure if this was ever a problem in the history of mankind however. Maybe I will bother trying if I come across a coaxial cable I was going to throw away because of damage.