Midnight Pub

Coaxial, the ancient wonder tech


Hi all, been a while -- I've been lurking mostly, but not adding anything -- time, energy, obligations, the usual excuses.

Wiring the apartment

I live in an old house, my apartment being on the second floor where I've been settling in for the last 6 months and the work still isn't finished.

For example: internet

Internet back in my home country was easy. You call one of the two monopolies to hook up fiber to your home, then someone runs a Belling-Lee[0] cable from the fiber hub to your modem/router, and then everything is just LAN (RJ45).

If you own the house, you can even start drilling holes and looping gigantic 30m ethernet cables all over the place, but you'll suffer a significant drop in signal.

If you want to split an ethernet cable later on, so that each bedroom has its own line, you can buy a powered ethernet switch box and run separate cables from it to your rooms of choice, where the switch box will do all the address translation for you, to seamlessly (okay, with some delay) make it seem that all your devices are on the same network

Enter Coax

Coax doesn't do address translation. Coax doesn't know what an address is. Coax is a single copper cable surrounded by plastic. Coax just vibrates on any frequency from 0-2GHz.

Need to split a cable to access different rooms? No powered switch box needed, you just split that motherfucker with a fork and pass the signal on. Coax doesn't give a shit about address translation.

Need to give every house on the street access to an internet hub?

You *could* independently run parallel ethernet cables from each house to the hub at considerable cost, or hierarchically distribute cables through various powered switch boxes spanning the neighborhood....

... or, you could get a single coax cable, hook it up to the first house, split it and run the cable to the next house, split that, run the cable to the next house, split that, etc. etc. You can literally hook up an entire neighborhood in series like a Christmas tree, assuming a loud enough starting cable.

And that's the thing - Coax is beautifully easy. It doesn't care how it's wired up, it just cares that you have a signal.

Back to the apartment

This apartment is structured in a difficult way. The living room and the office room are on opposite sides of the floor plan, so in order to run a cable from the router to the office, I'd have to lay down at least 50m of perimeter cabling with copious amounts of drilling or I'll have to start drilling holes in the ceiling and passing an ethernet cable through the floorboards of my neighbors (and I'm not sure I'm allowed to do that).


One option to solve this issue is to use a Powerline adapter[1], which is a device you plug into the electrical socket of one room and into the electrical socket of your other room, and the internet is encoded through the electrical signals along the powered wiring of the house.

In principle, Powerline is the ideal solution. Plug'n'play baby, yeah! In reality, Powerline is terrible. It drops constantly because the frequency it syncs to loses coherence, and many of the standard Powerline devices you buy don't auto switch to empty channels like WiFi routers do.

(On a separate topic -- yes I've tried WiFi extenders/repeaters to boost the WiFi across the apartment but this is also unreliable and any custom solutions has my neighbors knocking on my door asking why their WiFi is suddenly so weak)

Powerline also has a subtle constraint in that it works reliably if the source socket and the end socket are plugged onto the same circuit, otherwise the signal has to go all the way back to the switch box and negotiate an ad-hoc signal brokering solution there where it can finds the right target circuit. My office and my living room are on different circuits and so Powerline drops out frequently.

Coax again

One thing the living room and the office have in common is that they share a TV and Radio wall socket[2], which have an entry point to an antenna somewhere on the roof, and also an entry point from the cable internet to the house from the cellar.

That is, a splitter is used to combine these two different signal sources into the same cable for the house, which can then be split off into various apartments, where all endpoints will carry both TV/Radio and Internet in the same cable! (Suck it, ethernet!)

Some of you have made this far down might be scratching your heads and wondering "Uhh, won't those signals just blend together and create noise? How do you separate the internet out of the TV?"

At this point I will have slapped you across the face for taking Lord Coax's name in vain. The answer is, Frequency Division Multiplexing (FDM)[3]

Frequency Division what?

If you bundle these sources into the same cable, you can probably see that there is going to be some overlap in the frequencies used. This is only a problem if those frequencies use large banding (e.g. you use frequency 1500Mhz for all communication, which a channel size of 500MHz, meaning anything in the 1000-1500MHz range will be interpreted by you as "signal").

DOCSIS(1.0 to 3.0) [4] is a an FDM specification, that uses 6-8MHz bands. These are tiny, and give many possible channels for a signal to be used. If one of the channels is being used by another signal (e.g. TV or satellite), then your modem is smart enough to know that it should use a different channel. How awesome is that.

Even more awesome is that is your router can use many of these channels at the same time to double/triple/quadruple your throughput if needed. Wonderful tech.

Back to the apartment, back to Coax

Now I don't really watch cable TV nor the radio, so these sockets are used just to connect to the internet, but the important thing to note here is that these are coax sockets I can use to communicate with other coax sockets.

How? Through the power of MOCA[5], aka Multimedia over Coax (Alliance).

MOCA devices adhere to the MOCA specification which specifies a bunch of frequency channels in the 450-1625MHz range. These operate much like the Powerline adapters in the previous section, but instead of operating over the unreliable electrical circuit at noisy radio frequencies (0-500 KHz), they operate directly through the coax cables at a wide range of high frequencies.

Splitters are Filters

One important thing to note is that when you use a coaxial splitter, you are also applying a frequency filter of sorts between the source and the endpoint. At the point of contact of your house, usually there is a 0-1000MHz splitter between your cable box and your modem, meaning that the signal being received by your modem is already capped at 1000MHz.

This leaves the 1000-1600MHz range completely free for other things... such as MOCA!

If you run a MOCA device through the same coaxial cable that your internet comes through, it should be completely left alone by the internet frequencies.

Upgrading the sockets

This is where I am right now. My current sockets take a coaxial cable capable of 0-2000MHz ranges, and chucks out only TV and Radio outputs (i.e. Radio takes the cable and filters out the 0-200MHz of the cable, and TV filters out the the rest).

Currently to get internet to work, one can use a multimedia adapter[6,7] that converts the TV+Radio output into a TV+Radio+Satellite output (it splits the TV output into 200-500Hz and gives the 500-Rest to the satellite, and Radio is untouched).

I find this super annoying, inefficient, and also am worried that it's causing a loss in signal power (dB) at this point of contact.

So I'm replacing these with Axing 4-port SSD 7-00 wall plate[8] which incurs only a loss of 2dB at the point of contact, and gives two data outputs, one which I can screw the router to and the other that I can screw the MOCA adapter to.

Currently the router is being a baby about it, where it's taking close ~24hrs for it to scan and calibrate all frequencies for it to determine where the internet frequencies are, but I'm hopeful it will finish soon.

TL;DR (Summary)

I bought two MOCA devices and am running them from my office room to my living room, similar to a Powerline adapter, but much more reliable. Coax is an amazing, simple, and highly scalable piece of ancient technology.

Satellite TV is equally amazing, where you can get 60fps 720p quality TV signals from an antenna dish from signals bounced over a freaking continent.

Coax rules, LAN sucks. Go Team Coax.


Please see post 1351 for a small addendum to getting things working. Turns out that a router should not wait hours for a connection, and that I was adding noise to the network.


0: Belling-Lee Connectors
1: Powerline Communication
2: TV and Radio socket
3: FDM
6: Adaptor
7: Adaptor Pass Filters
8: Axing 4-port wallplate


Way more elegant than my solution: hang 50 feet of ethernet cable from the wall/ceiling with command hooks going all the way from one end of the apartment to the other.



I quite like that -- it has a distinct piratey feel to it that I admire



TBH I miss dialup internet over POTS. Sure, it was slow and there wasn't enough bandwidth to make streaming media and online gaming practical, but we also weren't sending 2MB of JavaScript for a 500 word blog post or news article paraphrased from Associated Press copy.



Amen to a lightweight decentralized internet. I mourn it everyday



As wonderful as coax is, I was nonetheless happier when taut kite string between paper cups ruled my communication world.



Signal-over-Acoustic-Resonant-Wire (or SOAR for short) (trademark pending). I wonder if it's possible to wire up a house with taught strings, and have exit points in every room. That way kids could hear the movement of the spiders in the walls, complemented by the background sound of their parents copulating in the night, and I think that's truly wonderful.

<sips coffee thoughtfully>



Finally: a string theory I can become interested in!