Fibre optic networking for observatories - a practical guide

[discardedastro]

Lots of people will reach for a long bit of Cat5e cable, maybe even outdoor-rated, when wiring a new observatory into their home. This can work, but can also lead to all sorts of Fun and performance issues over longer distances.

Fortunately there's an alternative that's more appropriate for permanent or semi-permanent installations - fibre optics - and it doesn't cost much more. Using fibre means no (active) electrical elements outside, simpler grounding for any armour, no risk of interference from mains or other electrical sources, and no distance limits.

I've ended up explaining bits of this a few times (my background is in fibre to the home optical architecture and engineering), so thought it might be helpful for some to have a single guide.

Firstly, a bit of a primer on fibre optics.

Terminating and splicing

Fibre itself is a very, very thin (125um) strand of glass, usually coated (250um) and then buffered within a gel-filled tube, which is then armoured or further protected with e.g. kevlar strands within a cable.

Putting connectors on fibre is very hard. Even professionals with tooling leave termination to labs; field termination is normaly done by splicing on a pre-made connector.

Splicing involves melting two fibres together while mechanically pressing them together. It requires specialist equipment (on the order of £2k for the cheap stuff) and skill.

All of which is to say - this is hard. But the good news is we don't need to do any of this, because we'll buy pre-made assembled cables!

Cleanliness

Connectors are easily damaged or affected by dirt and debris. Again, normally in a professional environment you'd use a microscope to check for cleanliness and to check cleaning results. We're talking short distances here, though, so in practice if you keep the dust caps on till you're ready to connect stuff, you'll be fine.

Fibre types

There's two types of fibre - single and multi mode. These differ in their core geometry, and by consequence the modes of light that can propogate within them.

In practice in 2023, ignore multi mode; it has limited applications and is falling out of favour even in those applications. Single mode fibres use near-infrared (NIR) light between around 1260nm-1650nm. This is what you want!

Connectors and cable types

All fibre terminates in connectors to connect to equipment or patch panels, keystone modules, etc.

There are many, many connectors out there. In practice all you need to know about is LC - small, 1.25mm ferrule connector often used for duplex connections - and SC, a 2.5mm ferrule square connector most commonly used for simplex connections (though that isn't what SC stands for!).

You also need to be aware that there are two polishes of connector - UPC and APC (PC is just like UPC, but worse quality - rarely found now). APC is angled polished contact, and is mostly used on passive optical networks like the one BT and others are building in the UK at the moment where reflections are important; APC bounces any reflections off into the cladding instead of bouncing it right back down the fibre. In practice - APC has green connector bodies, UPC is blue. You want UPC, or blue. Connectors on equipment are almost always UPC.

Cables come in many varieties, to suit different applications. You'll find the most readily available off the shelf are patch cords, which are meant for indoor use. However, lots of people will also supply pre-made armoured cables suitable for outdoor use or burial. Note that short and long cables may cost similar amounts at the low end of things - most of the cost of a cable up to 50-100m is not in the cable, but in the labour to terminate each end with its connectors.

Optical signalling and duplex vs simplex

The simplest optical link requires two fibres. Each fibre is used by one transmitter at each end, and a receiver at the other end receives the light. This is a 2-fibre duplex link.

However, we can save some cash by making the link a bidirectional fibre link. This uses bidirectional optics- which use a different set of coloured lasers in each direction and filter the light received at each end. This means we now only need one fibre!

This is the hot plan most of the time - it saves you some cash on the cable.

Transceivers/optics

Transceivers - also called optics - do the actual talking optically. They're normally plug-in modules, with electrical contacts on one side and a fibre connector on the other.

These modules plug into switches with "cages" to receive them, or can be connected into devices called media converters which act to just translate from copper to fibre.

You'll often see these "coded" for specific vendors - some switch vendors only support "their" optics despite it all being an open standard, so often people will sell you parts that look like e.g. Cisco's parts.

For gigabit systems the most commonly used format is SFP. 10 Gigabit systems use SFP+.

Transceivers are also the defining element (aside from cable/connector quality) that define how far you can reach. On singlemode optics, 10km is the very shortest you can get - and in practice these are actually 20km parts that didn't quite make the cut during test. If you're doing more than 20km you probably should go hire someone to do this all for you! But it does highlight one of the huge upsides - no distance limits to worry about in practice.

Recommended system

What do you actually need to hook up your observatory?

You need a few things. In order, this is how we get from a network switch in the home to a network switch in the obsy:

1. Switch port
2. Cat5e patch cable
3. Media converter 1
4. Bidirectional optic in media converter 1
5. Fibre cable
6. Bidirectional optic in media converter 2
7. Media converter 2
8. Cat5e patch cable
9. Switch port

So to summarise: two media converters, two optics, a cable and some patchcords. I'll show some links to fs.com below, who are a reasonable supplier and quite cost-effective, but other vendors are of course available...

Media converters can be had for cheap - £30 an end: https://www.fs.com/uk/products/104628.html?attribute=49020&id=751923

Into these media converters you'll need a matching pair of bidirectional optics: https://www.fs.com/uk/products/75336.html and https://www.fs.com/uk/products/75335.html?attribute=47458&id=740510 for instance. TX and RX should be swapped on one.

Cables are easy enough. Armoured assemblies can be had for less than £60 for 30 metres, e.g. https://www.fs.com/uk/products/70220.html

If you want to run a lot of cable internally you might want indoor-rated cable (EuroClass Cca, LSZH, etc). You can join cables together with couplers, which let you plug a connector into another connector; for instance, https://www.fs.com/uk/products/76103.html is suitable for coupling LC to LC.

Assembly is simple - plug it all together and switch it on. Now you have a reliable, fibre optic gigabit link from building to building, with no earthing issues to worry about!

If you're using armoured cable you should still attach the shield to ground, but this has no impact on signalling. You can do this at both ends or the end with the best ground.

 

Hope this helps and happy to answer questions and expand this if people find it useful!

[malc-c]

Sounds like you are you doing a sales pitch 🤔?

My observatory is around 50 feet away, and I used standard cat5  cable between the PC in the observatory and the switch in the house.  The cable was tacked to the fence and has lasted more than 13 years without any issues.  The home network is gigabite  speed which is ample for remote desktop sessions.

Totalling up the cost of fibre, there won't be much change out of £150 for a similar arrangement... but what would I gain... nothing as the fibre link is rated at the same speed, plus fibre is more fragile than cat5/6.   Now where you would gain is in distance, as the max cat6 length is around 100m.... but I don't know many who have 100m+ long gardens.

Edited January 25, 2023 by malc-c
typo

[discardedastro]

22 minutes ago, malc-c said:

Sounds like you are you doing a sales pitch 🤔?

My observatory is around 50 feet away, and I used standard cat5  cable between the PC in the observatory and the switch in the house.  The cable was tacked to the fence and has lasted more than 13 years without any issues.  The home network is gigabite  speed which is ample for remote desktop sessions.

Totalling up the cost of fibre, there won't be much change out of £150 for a similar arrangement... but what would I gain... nothing as the fibre link is rated at the same speed, plus fibre is more fragile than cat5/6.   Now where you would gain is in distance, as the max cat6 length is around 100m.... but I don't know many who have 100m+ long gardens.

I don't make any money from any of the above, I've just spent enough time explaining to people why their 150m bit of cat5 directly buried/submerged/nailed to fenceposts/jointed with wire nuts wasn't performing very well to feel like writing it down once to refer to...!

You're quite right though that on short runs, you can certainly get away with copper. I use copper for my own telescope (not an observatory, but left outside), but then it's a 10 metre patch cord! I use fibre for other runs - some IP cameras 100m away get DC power on some tri-rated cable and fibre for connectivity, for instance.

Fibre isn't actually more fragile - copper cable does need to be treated more carefully than fibre to maintain its performance, and is harder to verify if damaged. Armoured fibre cables are very robust, and modern fibre (G.657.A1/A2) has a minimum bend radius so small as to be practically irrelevant (50mm in the worst case). Copper has similar bend radius requirements, but also doesn't tend to recover if this is ever exceeded in installation.

In practice, if there's significant risk of lightning, or the structure is >50m away as the cable runs, fibre is more appropriate (as a rule of thumb).

Edited January 25, 2023 by discardedastro

[dwc]

Very interesting, thanks for taking the time to put this together. I’m familiar with the functions and limitations of Cat-5, but never really had an opportunity to get to grips with fibre. 

[iapa]

On 25/01/2023 at 17:19, discardedastro said:

Lots of people will reach for a long bit of Cat5e cable, maybe even outdoor-rated, when wiring a new observatory into their home. This can work, but can also lead to all sorts of Fun and performance issues over longer distances.

Fortunately there's an alternative that's more appropriate for permanent or semi-permanent installations - fibre optics - and it doesn't cost much more. Using fibre means no (active) electrical elements outside, simpler grounding for any armour, no risk of interference from mains or other electrical sources, and no distance limits.

I've ended up explaining bits of this a few times (my background is in fibre to the home optical architecture and engineering), so thought it might be helpful for some to have a single guide.

Firstly, a bit of a primer on fibre optics.

Terminating and splicing

Fibre itself is a very, very thin (125um) strand of glass, usually coated (250um) and then buffered within a gel-filled tube, which is then armoured or further protected with e.g. kevlar strands within a cable.

Putting connectors on fibre is very hard. Even professionals with tooling leave termination to labs; field termination is normaly done by splicing on a pre-made connector.

Splicing involves melting two fibres together while mechanically pressing them together. It requires specialist equipment (on the order of £2k for the cheap stuff) and skill.

All of which is to say - this is hard. But the good news is we don't need to do any of this, because we'll buy pre-made assembled cables!

Cleanliness

Connectors are easily damaged or affected by dirt and debris. Again, normally in a professional environment you'd use a microscope to check for cleanliness and to check cleaning results. We're talking short distances here, though, so in practice if you keep the dust caps on till you're ready to connect stuff, you'll be fine.

Fibre types

There's two types of fibre - single and multi mode. These differ in their core geometry, and by consequence the modes of light that can propogate within them.

In practice in 2023, ignore multi mode; it has limited applications and is falling out of favour even in those applications. Single mode fibres use near-infrared (NIR) light between around 1260nm-1650nm. This is what you want!

Connectors and cable types

All fibre terminates in connectors to connect to equipment or patch panels, keystone modules, etc.

There are many, many connectors out there. In practice all you need to know about is LC - small, 1.25mm ferrule connector often used for duplex connections - and SC, a 2.5mm ferrule square connector most commonly used for simplex connections (though that isn't what SC stands for!).

You also need to be aware that there are two polishes of connector - UPC and APC (PC is just like UPC, but worse quality - rarely found now). APC is angled polished contact, and is mostly used on passive optical networks like the one BT and others are building in the UK at the moment where reflections are important; APC bounces any reflections off into the cladding instead of bouncing it right back down the fibre. In practice - APC has green connector bodies, UPC is blue. You want UPC, or blue. Connectors on equipment are almost always UPC.

Cables come in many varieties, to suit different applications. You'll find the most readily available off the shelf are patch cords, which are meant for indoor use. However, lots of people will also supply pre-made armoured cables suitable for outdoor use or burial. Note that short and long cables may cost similar amounts at the low end of things - most of the cost of a cable up to 50-100m is not in the cable, but in the labour to terminate each end with its connectors.

Optical signalling and duplex vs simplex

The simplest optical link requires two fibres. Each fibre is used by one transmitter at each end, and a receiver at the other end receives the light. This is a 2-fibre duplex link.

However, we can save some cash by making the link a bidirectional fibre link. This uses bidirectional optics- which use a different set of coloured lasers in each direction and filter the light received at each end. This means we now only need one fibre!

This is the hot plan most of the time - it saves you some cash on the cable.

Transceivers/optics

Transceivers - also called optics - do the actual talking optically. They're normally plug-in modules, with electrical contacts on one side and a fibre connector on the other.

These modules plug into switches with "cages" to receive them, or can be connected into devices called media converters which act to just translate from copper to fibre.

You'll often see these "coded" for specific vendors - some switch vendors only support "their" optics despite it all being an open standard, so often people will sell you parts that look like e.g. Cisco's parts.

For gigabit systems the most commonly used format is SFP. 10 Gigabit systems use SFP+.

Transceivers are also the defining element (aside from cable/connector quality) that define how far you can reach. On singlemode optics, 10km is the very shortest you can get - and in practice these are actually 20km parts that didn't quite make the cut during test. If you're doing more than 20km you probably should go hire someone to do this all for you! But it does highlight one of the huge upsides - no distance limits to worry about in practice.

Recommended system

What do you actually need to hook up your observatory?

You need a few things. In order, this is how we get from a network switch in the home to a network switch in the obsy:

1. Switch port
2. Cat5e patch cable
3. Media converter 1
4. Bidirectional optic in media converter 1
5. Fibre cable
6. Bidirectional optic in media converter 2
7. Media converter 2
8. Cat5e patch cable
9. Switch port

So to summarise: two media converters, two optics, a cable and some patchcords. I'll show some links to fs.com below, who are a reasonable supplier and quite cost-effective, but other vendors are of course available...

Media converters can be had for cheap - £30 an end: https://www.fs.com/uk/products/104628.html?attribute=49020&id=751923

Into these media converters you'll need a matching pair of bidirectional optics: https://www.fs.com/uk/products/75336.html and https://www.fs.com/uk/products/75335.html?attribute=47458&id=740510 for instance. TX and RX should be swapped on one.

Cables are easy enough. Armoured assemblies can be had for less than £60 for 30 metres, e.g. https://www.fs.com/uk/products/70220.html

If you want to run a lot of cable internally you might want indoor-rated cable (EuroClass Cca, LSZH, etc). You can join cables together with couplers, which let you plug a connector into another connector; for instance, https://www.fs.com/uk/products/76103.html is suitable for coupling LC to LC.

Assembly is simple - plug it all together and switch it on. Now you have a reliable, fibre optic gigabit link from building to building, with no earthing issues to worry about!

If you're using armoured cable you should still attach the shield to ground, but this has no impact on signalling. You can do this at both ends or the end with the best ground.

 

Hope this helps and happy to answer questions and expand this if people find it useful!

Thanks, this expands very nicely on your comments on my build.

Ny network days were to the end of IBM’s Token Ring and early adoption if TCP/IS

Edited January 26, 2023 by iapa

[fozzybear]

40 minutes ago, iapa said:

Thanks, this expands very nicely on your comments on my build.

Ny network days were to the end of IBM’s Token Ring and early adoption if TCP/IS

Me also IBM Token ring and MAU's funky connectors, Crikey also early 4MB network. Then went Decnet.

[fozzybear]

My nextdoor neighbours son is installing the backbone Fibre in our village for Orange so plenty of fibre joints and we are to get 10G EPON 8Gbits/s download and 700 mbit/s upload so happy times

 

[powerlord]

It is a bit overkill, ethernet will run 100m easy. And shielded cat6 is available if required.  If you want 10gb then go fibre, but otherwise...does seem a bit overkill - but nowt wrong with that if it floats yer boat! 🙂

 

[discardedastro]

7 hours ago, powerlord said:

It is a bit overkill, ethernet will run 100m easy. And shielded cat6 is available if required.  If you want 10gb then go fibre, but otherwise...does seem a bit overkill - but nowt wrong with that if it floats yer boat! 🙂

 

Ethernet will run 100 metres quite readily, yes - in theory

However, here's the thing; how that Ethernet cable was installed will determine how well stuff runs over the Ethernet link. This is one of the great challenges in copper cabling (and why things called cable certifiers exist, and form part of any competent cabling installation work in the commercial world - because they can verify the RF performance post-installation).

Cat6 and Cat6A run as far as each other; Cat5e runs shorter distances at higher speed due to lower RF performance. 6A is practically irrelevant for homes, because the situation for which it was designed - high alien crosstalk - will never occur. Shielding only really factors in when you have bundles of dozens or hundreds of cables running alongside each other (causing noise between 10-600MHz) - this happens a lot in large businesses and datacentres, but rarely otherwise. Save your money and don't bother with shielding for home! 50Hz from mains simply doesn't matter; Ethernet over Cat5e can reject this just fine (induced DC voltages aside).

If you kink the cable, even temporarily, beyond its bend limit during installation; or over-strain it, or secure it with clips that pinch it too tightly, you can very easily deform the copper and this will have an impact on performance. The interesting thing is that it has to be really bad to be visible easily. You'll plug those things together, and they'll negotiate a gigabit link! The negotiation only requires very basic signalling at low speeds. If you start using this on a LAN, it'll be fine. If you then try and actually throw gigabit speeds around, particularly with protocols based on TCP, if the cable isn't performing well you'll see performance fall short. Frames will be dropped; TCP will start retransmitting more. Applications like INDI or ASCOM will start having to work harder (at the transport layer) if they're working on a link which is dropping packets/frames.

This is, incidentally, a significant problem for ISPs offering gigabit speeds! Lots of people have home wiring which is just fine at 100Mbps or 80Mbps or whatever their home internet can provide. Then they upgrade, their home internet can do 940Mbps, and suddenly they complain they can't get more than 300Mbps on a speed test while plugged in at the back of their house over some Ethernet installed by a telephone/aerial engineer a decade prior, even on a short run...

Fibre is actually rather a lot more forgiving in a lot of respects! While older glass was hard to handle, modern cables using G.657.A1 or even G.657.B1-3 have better bending radius limits than copper and suffer no appreciable damage if radius limits are exceeded temporarily during installation. Some fibre cables can tolerate being stapled directly to walls or bent less than 5mm.

And crucially, on short links - under a kilometer - even if you damage the cable quite badly there's enough link budget left for everything to work. A typical gigabit transceiver has a launch power of around -3dBm, and a receive sensitivity of -23dBm. This means you have 20dB of link budget. For reference, a "bad" fibre fault might introduce between 1-3dB of loss, and you normally lose around 0.3dB for every 1000m of cable. Compare this to copper where a "perfect" installation of a Cat6 link might have about 0.5-1dB of link budget remaining - and remember dB is a log scale!

You can mess up really, really badly on a fibre link over short distances (up to 3-5km) and not notice a thing. Kinks/macrobends, dirty connectors full of mud, etc etc. If you don't unwind the cable properly while installing 100m of copper and induce a kink, you can easily fail to achieve much more than 100Mbps of performance. So that's where fibre can really provide a benefit over copper on longer cable runs.

[dk101]

I am not familiar with the UK wiring rules but is it ok to put a copper network and mains power cables through the same conduit underground? I hear that in some countries this is a no-no and this is where fibre comes in to play as fibre data can go with mains power while copper would not be allowed.

Is this even an issue over here?

 

[discardedastro]

2 hours ago, dk101 said:

I am not familiar with the UK wiring rules but is it ok to put a copper network and mains power cables through the same conduit underground? I hear that in some countries this is a no-no and this is where fibre comes in to play as fibre data can go with mains power while copper would not be allowed.

Is this even an issue over here?

 

I don't think it matters by the book - I have a copy of the regs but I'm not a practitioner!

Over short distances in practice it'll be fine, I think.

Over longer distances, there is risk of induced current causing problems with potential difference between ends, and grounding etc becomes problematic.

There is a practical benefit in terms of electrical safety if you're just considering the network cable, which is lightning protection. I have seen cases of lightning hitting one building and toasting the network (in one case where the conductor of a lightning rod ran parallel to a bundle of Cat5e, without direct connection toasting a whole office's worth of computers). But if you're running mains alongside - which is likely - there's probably not much benefit.

[DaveL59]

The other issue with copper cat5e and other LAN cable is when it's not really copper. CCA is quite common esp in cheaper cables like the rolls bought at DIY places and the like. While it'll work just fine, initially, environmentals can have a big impact on lifespan when the copper coating breaks away from the aluminium core. Also it isn't a good idea to use CCA if you plan do do PoE esp if the end load needs a reasonable amount of current. CCA could then overheat and cause fires.

As far as environmental issues with LAN cables, corrosion at the plug/socket can be reduced by using dielectric grease but be warned that if you plug/unplug often as in setup/break down your kit nightly etc, that grease will get on your hands and anything the cable end contacts with so could leave you with a major optical cleaning task before you know it. It does work well tho, I've a couple cameras outside and no issues with the LAN/BNC connections in the 4+ years they've been operating.

[Lumos]

I initially started installing fibre for all my external runs in SW France as we get violent storms and all our neighbours are forever replacing equipment that has suffered from lightning damage. Fibre not as susceptible to induced voltages in the same way as ethernet cable. I also like the fact the manufacturer will pop as many fibres in as you want and there is no real difference to the thickness. In France yo cannot bury electrical cables with Cat6, not that I would want to, but as mentioned, the mains voltage is not going to induce anything in the fibre.

 

It seems daunting before you do it and after it seems the only sensible approach.

[Bukko]

I seriously considered fibre runs for my installation a few years ago - Maybe I looked in the wrong place, but found the costs pretty expensive. I do have around a 50m run from the house to the observatory, plus local runs of around 10 and 15m. I was concerned that any patch fibres I purchased might be too short, so estimating plus 20% seemed like a good idea.

In the end, I opted for Cat5e and have no ptoblem running at a full gigabit per second. With SSD's on each PC, transfer rates are sustained at 100MB/s.

For redundancy, I installed two cables per run, in case a mouse eats one, but so far, so good. The main run from the house is in a trench and for about 15m, the power is shared with the Cat5e cables. The different cables are in separate conduits, about 20cm apart and any small amount of induced voltages in the Cat5e is unlikely (And in practice, I have had no issue).

I have suffered a lightning strike close by the house. None of the network components failed, but I did lose a PC and camera. I also think I suffered some electronics damage to a mount and have noticed some degradation in functions since. I use several UPS units to offer some protection and working on installing some ground rods and hoping this will help prevent another incident. But a thought in my mind is telling me I might end up offering a better ground than the surround and end up attracting another strike...

But back to the fibre optic thread, if I was doing it again, I would work harder on specifying fibres, I think.

 

Gordon.