braid strap  - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: November 13, 2024, 05:07:31 am
content: I wanted to know about the rf properties of braid straps.I have seen it referenced before in some documents relating to things like LISN test setups.I got some 3/16 braid (tinned) to maybe do some VNA or impedance analyzer experiments with.I thought it might be similar to a sheet of copper, but with skin and proximity effects I really don't know how to compare it.Like if I see a deal on braid, I have no idea if I should buy it. Normally I would make cuttings out of a copper sheet like I have seen in some older RF equipment.An interesting application is to use braid as a return for a BNC connector that uses a solder lug, or possibly making a better star ground between multiple circuit boards.I feel like most people would just rip it out of a cable.. but I wonder who here has flat strap in their wire cabinet.

author: Randy222
author_rank: Frequent Contributor
timestamp: November 13, 2024, 03:56:19 pm
content: Are you asking about using flat braid as the transmission line?

author: coppercone2
author_rank: Super Contributor
timestamp: November 13, 2024, 09:38:48 pm
content: I think its more of a ground connection, though putting a signal through it is interesting I guess.In the strictest sense then I guess you are rightI was thinking more along the lines of prototyping, where it might not be practical to have a 'ground plane' for a circuit. The strap can get around much better. Something between a bus bar and a ground returni.e. in my empire antenna with its preselector transformer, they used a carefully cut copper sheet inside of the 'chassis' to get RF performance from something that is not a circuit board. IIRC it was connected to rotary switches and had a interesting shape. But if I were to try to build something like that, it seems like being able to use braid would be alot better then figuring out how to make that copper...When I built a loop antenna a long time ago, you needed to make a connection from the antenna ends to a circuit board. Of course wire works, but I think if they sold it, it would have had carefully cut and formed copper sheet to connect to the board. But braid could be used here too with less work. I just don't know how exactly it compares.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: November 14, 2024, 12:28:56 am
content: No such thing as ground, only more antennasBraid is a low-inductance antenna because it's flat and wide compared to a wire. It's probably not quite as good as a sheet of copper, but convenience of being flexible makes up for it.Of course you end up with transmission line effects as soon as you start approaching a reasonable fraction of a wavelength.

author: coppercone2
author_rank: Super Contributor
timestamp: November 14, 2024, 01:11:39 am
content: for lower frequencies, I thought it might be better then a sheet of copper in some cases, because of some people saying there is litz like effects that come with strands. However, the woven nature of braid makes whatever residual litz like effect that it might have might be further diminished by all the curves, wires are usually not woven for integrity like braid is, and while similar to coaxial cable, i don't think people ever consider the behavior of the coaxial shield by itself as a conductor so there is not that much information on it

author: ejeffrey
author_rank: Super Contributor
timestamp: November 14, 2024, 03:43:01 am
content: The problem with braid is that due to skin effect the current keeps hopping between strands to stay at the outer edge. If the braid is new and clean the resistance of those junctions might be fine. As it oxidizes, the RF resistance increases.Tinning a braid turns it back into a solid piece but one made of tin alloy not copper. At that point the copper is just mechanical support

author: coppercone2
author_rank: Super Contributor
timestamp: November 14, 2024, 05:15:29 am
content: I guess you need to go silvered or go home

author: coppercone2
author_rank: Super Contributor
timestamp: November 14, 2024, 09:04:55 am
content: another interesting property of braids is that you can kind of thread component leads through them, solder it on very carefully, and have something almost like a highly flexible ground plane, so long you use fine wire to join the components.Not sure what kind of whacky uses there are for that, but its another dimension.To me it means DIY flex power circuits with a high level of performance. I think it has less constraints then most simple flat flex substrates. It even may be possible to surgically cut into the braid, and form a micro ferrule type crimp with a component lead with the braid wires itself, but this would require a special crimp tool and some serious analysis. But at least its something to think about.

author: virtualparticles
author_rank: Regular Contributor
timestamp: November 26, 2024, 11:32:11 am
content: Quote from: ejeffrey on November 14, 2024, 03:43:01 amThis is a really perceptive answer. I know that electron conduction relies heavily on tunneling, but haven't thought about what goes on in a braid...