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Comment by cyptus | Hacker News Reader

_minimum_ bend?

minimum bend _radius_

A straight cable has an infinite radius, the more bend the smaller the radius

Though if it is on or under the surface of the earth, “straight” will be a bend radius of around 6,370km. We don’t make a lot of buildings that deal with this but transcontinental or transoceanic cables certainly do. If someone designed a fiber that required absolutely no bend in order to work you’d have to use it in buildings or dig much deeper holes.

There was an encoding mechanism proposed about 10-15 years ago that used spirally polarized light to carry more channels, but it required the surface of the fiber to be polished to a much higher degree than existing cables in order for the light to go around bends properly.

If you’re using the planet as your “flat surface” then sure. If, however, you’re willing to deal with exiting the atmosphere at each end, you can use Real Straightness. But I don’t know anyone running a single segment for that distance.

I’m sure there are some microwave antennas still out there doing the Lord’s Work. At least in the Plains states where hills are low and putting antennas on two of them gives you some extra distance. How far do microwaves bend over the horizon?

Don't they generally do the opposite of bend over the horizon? Two towers that are observed (visible wavelength = tiny Fresnel zone) to have line-of-site can easily be obstructed (microwave = huge Fresnel zone).

https://en.wikipedia.org/wiki/Fresnel_zone

> How far do microwaves bend over the horizon?

that depends on the weather and frequency among other things

https://en.wikipedia.org/wiki/Line-of-sight_propagation

If you're going out of the atmosphere may as well skip the fiber and just point lasers through the vacuum of space directly and reap the benefits of the faster speed of light through a vacuum vs glass!

works great until a group of space bats get in the way.

Fibers can be bent to a radius of an inch or so, that's the tolerated minimum bend radius.

I guess you could call it "the maximum sharpness tangency" or something like that, but that's not the standard verbiage.

G.657A1, which is basically the crappiest you would ever buy at this point, is not even half an inch bend radius.

Minimum bend radius.

It’s usually 20x the outer diameter of the cable for fiber, a cable with a .3 inch OD has a 6 inch minimum bend radius.

What?

This is 100% wrong.

This is well standardized. As I posted elsewhere:

G.657A1/B1 = 10mm (half an inch)

G.657A2/B2 = 7.5mm (a little over a quarter inch)

G.657A3/B3 = 2.5mm (less than 1/8th of an inch)

The only cable you will find with a 6 inch bend radius is going to be armored interlocking fiber cable or something.

You can take 2mm G657.A3 fiber cable, wrap it around a pencil, and it will work 100% fine.

Even old G652 cable only had a 1 inch bend radius.

If I am wrong, then explain why this 24-strand plenum rated fiber optic cable has a minimum bend radius of 5.9”: https://leviton.com/content/dam/leviton/network-solutions/pr...

Part number: LTP12B024

I am running a project where the low voltage contractor is pulling this fiber cable into a conduit my electricians are installing.

I don’t doubt your bend radius claims on the fiber optic cables you listed, but there are far more types of fiber cable than the ones you listed.

There are not far more types of fiber cable, there are far more types of jackets :)

You are confusing the cable jacket with the fiber cable inside of it. This is the spec on the jacket they use and they didn't design this particular jacket to be flexible enough to survive flexing at the level the fiber cable inside of it can. Sure - not all jackets can be bent as much as the fiber. Some because they are not made to be as flexible (as here), some because it's basically impossible (armored interlocking jackets), etc.

I'm not sure what this changes?

The part number with suffix AB0403 (the SMF A1 fiber), if you cut the jacket, you should be able to bend the fiber cable inside at a radius of 10mm and have it be fine. It appears to be standard G.657A1 fiber cable inside.

There are really not far more types of fiber cable than i listed, and this spec sheet definitely does nothing to support that claim, since as i said, it has A1 fiber cable inside the cable jacket that will happily support a 10mm bend radius.

BTW, as an aside, I wouldn't use this stuff - just looking at this sheet and pricing at my normal fiber distributors - it is both overpriced and underspec'ed for its price. Which seems pretty typical for leviton :)

Most 24 standard I/O plenum cable is going to be 7.8mm (this is 9.9, so 30% thicker), and have less than half that bend radius even with non-flexible OFNP rated jackets. If you are being charged more than 2 bucks a foot for it, you should consider other options.

> There are not far more types of fiber cable, there are far more types of jackets :)

Ahhhh, thanks for clarifying! Now I understand what you’re saying, the jacket and fibers have different bend radiuses (radii). I appreciate you taking the time to explain :) also, noted about there only being a few types of fiber, with a multitude of jackets.

I’ll let my low voltage subcontractor know about the underwhelming Leviton cable, it’s a plan and spec public job so it’s possible the Leviton rep is friends with the engineer and got their cable flat specced, wouldn’t be the first time!

I’m only responsible for the raceway, it’s a 2500’ run between two college campuses separated by a highway that runs outside for a good chunk of the distance so it’s possible the jacket is beefy and inflexible for temp resistance. I’m much more familiar with electrical conductor jackets, THHN and XHHW-2, which are PVC and XLPE, respectively.

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