heavy walled semi ridged coax - Page 1
Forum section: electronics / projects

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 20, 2017, 07:40:59 pm
content: Most semi rigid cable like RG401 has a very thin outer copper jacket like .025" does anyone know of of a semi rigid cable with a way thicker jacket thickens. I want be able to use a a compression fitting on it without the tube buckling.

author: calexanian
author_rank: Super Contributor
timestamp: April 20, 2017, 08:18:08 pm
content: Have had good luck with Times Microwave products. You can use either their fancy clamps and bushings, or use conduit cable gland fittings. For the glands I like Heyco brand. With the glands its all rubber/plastic in contact with the jacket so you don't have to worry about it cutting and shorting.

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 20, 2017, 08:45:05 pm
content: This need to be a pressure tight fitting. A watertight cable gland just isn't going to cut it unfortunately. I'm basically trying to make a poor mans pressure rated RF feedthrough

author: calexanian
author_rank: Super Contributor
timestamp: April 20, 2017, 10:25:20 pm
content: Quote from: qwaarjet on April 20, 2017, 08:45:05 pmPoor man and RF seldom work out.

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 21, 2017, 12:34:54 am
content: Well this is a prototype

author: edpalmer42
author_rank: Super Contributor
timestamp: April 21, 2017, 03:17:12 am
content: How much pressure are you talking about?The cable companies use 3/4" 75 ohm coax with a seamless aluminum sheath. I just checked a datasheet and it showed a sheath thickness of 0.036".Maybe you should be looking for a bulkhead mounted connector or adapter. It's easy to find BNC or N connectors that have an o-ring. It's probably intended for water/dust proofing, but if the pressure isn't too high - maybe. Another possibility might be an adapter equipped with a mounting flange. You'd have to figure out a gasket on your own.Another consideration is the cable itself. Can gas leak through the cable around the dielectric?Ed

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 21, 2017, 03:35:16 am
content: The pressure is... high ( like don't want to be in the same room with it), cant go into that much detail unfortunately. There are some connector I found for deep sea applications but the form factor really sucks and the cost and lead time is impractical (mainly lead time). I haven't had any leaks of the cable on early attempts but the possibility of small leaks is acceptable at this stage of development.

author: metrologist
author_rank: Super Contributor
timestamp: April 21, 2017, 03:42:11 am
content: Can you solder the connectors? Maybe you can find some rigid or ruggedized cables, or roll your own from the plumbing department?

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: April 21, 2017, 03:51:25 am
content: Is the application narrow band? A bit Rube-Goldberg, but consider waveguide.

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 21, 2017, 04:16:56 am
content: Quote from: metrologist on April 21, 2017, 03:42:11 amSure I can solder, cant find a connector that can survive the environment I'm putting it in that cost less than a cheap car and take 12week to arrive thoughQuote from: metrologist on April 21, 2017, 03:42:11 amI already crushed what I would considered a rugged cable (RG401)Quote from: metrologist on April 21, 2017, 03:42:11 amthat was first thing I did but couldn't keep the impedance controlled thus I search for semi ridged coax that could double as a pry bar

author: edpalmer42
author_rank: Super Contributor
timestamp: April 21, 2017, 04:35:08 am
content: Feedthrough capacitors with a differential signal?Glass or plastic covered port with horn antennas on opposite sides? Modulate your signal onto a microwave carrier and transmit it through the glass.You're just not giving us enough info to really help.Ed

author: qwaarjet
author_rank: Regular Contributor
timestamp: April 21, 2017, 05:37:25 am
content: A piece of semi ridged 50ohm works very well for my application the outer jacket is simply too thin on the COTS cables I found so far, it buckles at the compression fitting. That's why I'm trying to find heavy wall. Ideally I would take rg401 and replace the outer jacket with 100mil thick stainless steelI do feel very sorry for not being able to be more specific about my application, but I appreciate the help this forum gives me since most questions I ask are for weird pieces of unobtanium.I have severe space restrictions and need broadband performance, waveguides and dielectric windows don't fit and can't take the the pressure. If you have a source for compactimpedance controlledfeedthroughs that can take very high pressure I would be interested. But the incredibly few I've found so far are very expensive and a multi month lead times and frankly would be a pain to work with since they are made for keeping pressure out not in (see ocean floor equipment) .But in general high pressure and RF don't seem to be a common application, vacuum on the other hand there is huge variety of products. And in a past life I had great success using a semi rigid and swag-lock for a vacuum feedtrough /RF plasma probe

author: slurry
author_rank: Regular Contributor
timestamp: April 21, 2017, 05:58:11 am
content: It's really hard to come up with solutions with so little information.What about semi-rigid inside copper brake tubing?

author: metrologist
author_rank: Super Contributor
timestamp: April 21, 2017, 03:59:41 pm
content: Make a cavity for the commercial cable to pass through. Add a second wall around your coax that can take the pressure of your crimps or can be welded itself.I mean if you took a foot long pipe and epoxied your coax in that, would that be strong enough? Maybe you can use a larger copper pipe with flange connectors soldered onto end caps.or work on your impedance problem?