Corrugated coaxial cable vs other shielding methods - Page 1
Forum section: electronics / general

author: matthuszagh
author_rank: Frequent Contributor
timestamp: August 06, 2021, 01:14:13 am
content: What are the applications of corrugated shielding for coaxial cable in comparison with other forms of shielding? Wikipedia (https://en.wikipedia.org/wiki/Coaxial_cable#Construction) has the following to say about coaxial cable with a corrugated shield:QuoteBut, when I was looking on Pasternack I found for example this (https://www.pasternack.com/50-ohm-low-loss-corrugated-1-4-superflexible-helical-coax-pe-1-4sfhc-p.aspx). It supports a max frequency of 20.4 GHz, which is well above the 1 GHz mentioned by Wikipedia.I would assume this solid outer conductive shield would reduce the flexibility of the cable, but this cable has a minimum repeated bend radius of 1 in., which seems pretty good. The rest of the specs also seem good and the price is in the middle of the range compared to some of their other cables.What are the drawbacks of this cable? When would I not want to use it? For example, is cable assembly more difficult with this cable (I only care about this with respect to a manual crimping process).The cable outer diameter is a bit on the large side, so maybe this is the main drawback?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 06, 2021, 06:11:50 am
content: Maximum frequency is set by acceptable losses, and "breakup" caused by additional non-TEM0 modes. Wiki is probably erroneous. Maybe their source explains in better detail (anyone got that edition handbook?), or maybe it's also erroneous.Losses are determined by construction, generally with larger build having lower loss, and also smoother metal faces (especially silver plated), and higher-Q dielectric (or the lack thereof -- as with foam, spiral or other sparse supports). The design choice is generally to use the largest line you can, up to the TEM cutoff, given cost, loss budget, and other considerations like available space, flexibility, etc."Cutoff" is not that it stops transmitting signals, but that it stops being as well-behaved of a medium -- specifically what happens is, as higher order (waveguide) modes come into play, their impedances and velocities are all different, and so the signal arrives at its destination over a range of times -- it becomes smeared out, dispersed; hence the property is called dispersion (when velocity depends on frequency).Tim

author: Bassman59
author_rank: Super Contributor
timestamp: August 06, 2021, 05:41:31 pm
content: Quote from: matthuszagh on August 06, 2021, 01:14:13 amBack when I was doing work with high power microwave transmitters, we used 25 mm-thick Andrew Heliax cables from the amplifiers to the antennas. This cable had corrugated shields.Why? These transmitters were powerful and the cable had to handle the power with as low loss as possible. That dictates the cable geometry and the shield thickness. But the cables had to be transported (on big spools) and installed, which meant that they had to be flexible to some degree. A solid shield that could handle the power won't flex. Hence the use of corrugated shields. The shields are like an armadillo's shell.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2021, 08:20:14 pm
content: The cutoff frequency is the first higher order mode. Applications which do not excite the higher order modes or are tolerant of them can operate above this frequency. Increasing the cutoff frequency means using smaller diameter cable with a greater loss.Corrugations in the inner and outer conductor, and non-uniform support of the inner conductor as with helical construction, and bends cause distortions in the group delay. Sharp bends are worse than gradual bends.