Need Very Flexible 50Ω Coax

Thread Starter

SamR

Joined Mar 19, 2019
5,060
I need to make some RF probe and instrument coax cables. I have some old RG-8X coax that I can cut pieces out of that is pretty flexible but what is the coax used to build scope probes? It's a lot smaller diameter than RG-8X and very flexible. Any ideas? I do have some RG-142 double shielded 50Ω coax but that stuff is pretty stiff (solid #14? center conductor) although about the same diameter as RG-8X. I do like the idea of well shielded instrument cables. RG-316 seems pretty small in diameter but is a possibility that I'm looking at.
 

Jon Chandler

Joined Jun 12, 2008
1,072
Some RG-174:has a copper-plated steel core. Avoid this version (RG-174 with a steel core) where a cable with be flexed a lot. The steel core can slice through the dielectric when heavily flexed, resulting in shield shorts. You've not had a headache until you try to troubleshoot this.
 

Thread Starter

SamR

Joined Mar 19, 2019
5,060
I went ahead with what I had which is some RG8X for the lead and a piece of RG132 for the tip since it has a solid center conductor. The Heath T-3 signal tracer I restored was missing it's leads so I used the manuals schematic and instead of a switch shorting the 1N34 diode I built both an RF and an AF probe. I did use 630V poly caps since this will be used around tube gear. Used 3/4" copper pipe and end caps for the probe bodies. Almost finished but discovered the male BNC connectors I have are for RG59 and the RG8X is too big for their ferrule. Always something. Used 2.5mm solder wick braid for the front ground connection and also ran a piece out of the back cap to solder to the body to ground it to the coax braid and circuit ground. Will also put some heat shrink around the body when I get the right size in. Used 6" piece of coax for the probes and may shorten them if needed. I'll see how these work before modifying with better coax.

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