look for 50ohm coax cable with extra 2,3 or more wire cores in the same jacket. - Page 1
Forum section: electronics / beginners

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 04, 2016, 05:34:20 pm
content: i somewhat managed to find it in ebay using keyword "multicore coax" but its 75ohm, and big fat in dimension. i prefer 50 ohm and smaller than or at least 8mm OD (similar to that i found in ebay), comfortably flexible if used as say dso probe cable. i'm thinking to find this item for my diy active probe, the power will come from the extra cores in the jacket to the probe tip. the psu will be plugged in at near the dso end, so my probe will become neater 1 wire probe instead of plugging the psu to the probe tip using separated wires. if you are confused with my broken english, the thing looks like...except neater, ie preferably smaller, and the crucial part is its a 50ohm impedance the coax inside it. whats the proper name for this? so i can check in digikey, element14 or ebay.since i'm at this, question... can we use 75ohm coax as dso probe cable? driven by 75ohm source (opamp) impedance and terminated with 75ohm resistor at the coax (dso) end? with not so detrimental result? if yes, then the 75ohm coax cable i found in ebay maybe an option. thanks.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 04, 2016, 05:35:33 pm
content: only one coax in the jacket (not many coaxes), the rest are normal wires for power supply (or near DC) purpose. i hope you know what i mean..

author: cowana
author_rank: Frequent Contributor
timestamp: May 04, 2016, 05:41:09 pm
content: Can you not use a DC bias on one bit of regular coax as power and for signalling (different analogue voltage = different signal)? That's the normal way something like this would be done.I'd be wary of using cable like the one you pictured for a scope probe - the 75R impedance is likely to be very variable and inconsistent across frequency.Andy

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 04, 2016, 05:52:35 pm
content: thats why i ask..

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2016, 06:02:22 pm
content: If this was a one-off I'd just make my own: strip the outer jacket, add the additional cores and cover with heat shrink.

author: wraper
author_rank: Unknown
timestamp: May 04, 2016, 06:39:04 pm
content: Quote from: Hero999 on May 04, 2016, 06:02:22 pmThat will completely suck, cable will be so stiff than barely usable. Appearance will be far from the best too.

author: wraper
author_rank: Unknown
timestamp: May 04, 2016, 06:47:14 pm
content: Appear to be plenty on alibaba, though minimum quantity is like 5 -10 km.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 04, 2016, 07:06:44 pm
content: Quote from: Hero999 on May 04, 2016, 06:02:22 pmyes as wraper said, heat shrink it is too stiff. if heated, it will follow the shape of whatever inside, ie not round. if not heated it will pinched/folded at bent region, in both case it is stiff...Quote from: wraper on May 04, 2016, 06:47:14 pm50ohm? can you give the link? i also saw the 75ohm type in ebay sold as a roll, length in km... certainly not the quantity and esp the cost i want.i wonder where the brand name active probe maker like tektronix and hp agilent got their supply from...

author: klunkerbus
author_rank: Unknown
timestamp: May 04, 2016, 07:16:19 pm
content: Quote from: Mechatrommer on May 04, 2016, 07:06:44 pmHaving been involved in a scope probe design many years ago, I'll share that the cable is likely custom. Heck, it was for the small test equipment company I was working for at the time. Generic coax just does not work well for scope probes. Tends to be too microphonic for one thing.EDIT: Granted though, this was on a passive probe, not active.

author: wraper
author_rank: Unknown
timestamp: May 04, 2016, 08:11:47 pm
content: Quote from: Mechatrommer on May 04, 2016, 07:06:44 pmhttps://www.alibaba.com/product-detail/Coaxial-Cable-RG-174-RG-174_60222687642.html?spm=a2700.7724857.29.42.kNwbsshttps://www.alibaba.com/product-detail/RG174-2C-50-ohm-camera-cable_60131580131.html?spm=a2700.7724838.0.0.20lX9m

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 04, 2016, 09:53:58 pm
content: Doesn't have to be heat shrink. Maybe something like braided wire sleeve, which would look pretty good too.