telescoping strait BNC to BNC extender? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: September 09, 2018, 01:33:00 am
content: Do they have such a thing? I think the back of my network analyzer has a telescoping right angle BNC to BNC adapter. IIRC it has a little collet you tighten or screw to adjust the spacing (HP part). unfortunately there is a major traffic jam in front of the network analyzer at the moment.I would like a strait one for bridging shield cans that have BNC on them.

author: David Hess
author_rank: Super Contributor
timestamp: September 10, 2018, 07:07:24 pm
content: I do not remember seeing them commercially available but I have seen them made from scratch using brass tubing to make two air lines which telescope together.The RF guys have something similar for adjusting phase but I have never seen it with BNC connectors.

author: coppercone2
author_rank: Super Contributor
timestamp: September 10, 2018, 08:21:36 pm
content: hmm so you just use the thinnest kind of tubing to make the air line?I suppose I can make my own part...I am guessing its silver plated. But do they sell tubing that would do the job or do you need a custom extrusion? or deform it slightly so its two ovals?

author: David Hess
author_rank: Super Contributor
timestamp: September 13, 2018, 03:16:12 am
content: The tubing is selected to make a 50 ohm air line and then the next size larger or smaller is used to make another air line which can slide in and out of the first one. Fingers are added at the sliding seam to make a good connection.

author: coppercone2
author_rank: Super Contributor
timestamp: September 13, 2018, 09:41:10 am
content: any idea what upper frequency limit you get before the fingers start to pose a problem? From previous investigation I see that fingers might be a difficult thing to determine accurately.

author: David Hess
author_rank: Super Contributor
timestamp: September 13, 2018, 01:23:51 pm
content: I have seen home made ones without fingers used up through 500MHz without problems in transmitter applications at 10s of watts. Variable tuning stubs with fingers for detector diodes are constructed in a similar way and are good to at least several GHz.Coaxial slide attenuators can be constructed in the same way except that the center conductor diameters are selected so that they do not touch.

author: coppercone2
author_rank: Super Contributor
timestamp: September 13, 2018, 04:02:49 pm
content: that should be more then enough. The reason for this is I wanted to do experiments with nested shields and stuff, so it would be nice to be able to disconnect subassemblies without having to unscrew them, otherwise it looks like I would need coaxial cable loops so they are not bent in bad waysI am starting to think about leakage though, with sliding ones, it might be worse

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2018, 03:03:25 am
content: Coaxial cables and BNCs leak also but this can be improved considerably with doubled shielded coaxial cable and threaded connectors.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 03:10:51 am
content: does the cheap F-connector do well in this regard? (instead of TNC for something like power supply)I am not sure how synonymous microwave performance S parameters are to suspectance from external fields, I think there can be a horrible mismatch but still good rejection.

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2018, 03:43:24 am
content: I suspect F connectors are even worse than BNCs because they lack a separate surface for the RF shield but I have always avoided them where this might matter. BNCs in good condition are almost always acceptable but if not, TNC and N connectors are a great improvement.I have difficulty imagining leakage causing problems with s-parameter measurement but maybe someone else who knows can comment. I have had to use double shielded cable when making sensitivity and minimum detectable signal test.