Running ethernet over Van Damme 268-307 6 x 75 ohm cable

A decade or two ago, there was some hype about running 10 Mbit/s Ethernet across a single 75 ohm MATV/CATV cable. In 10 Mbit/s the carrier sense and collision detection (CS/CD) was well defined.

If you have two 75 ohm coaxials, then you can forget the CS/CD issue and run unidirectional links in each cable. Twisted pair to 75 ohm coaxial using baloon transformers should do the trick.

If you can use two cables, a 100 Mbit/s connection should go fine using one cable for uplink and the other for downlink.

At least here (Northern Europe), there are TV antenna adapter cables with a RJ-45 at one end and a 75 ohm coax connector at the other end (and a balun inside). You'll need some RJ-45 connectors to branch the pairs to the adapters at each end of the link.

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-TV

snipped-for-privacy@downunder.com wrote

That is above my pay grade; I know analog but know almost nothing about the way ethernet (RJ45, 8 wires) communicates.

You can solve this using MoCA. These are adapters to run ethernet over in-house COAX installations made for TV. Different levels exist that can do 100 Mbit/s and even like 500 Mbit/s.

20m is no problem. I ran this for a while on a cable like 150m long, and it worked perfectly.

Rob wrote

Thank you. I bought a couple of IB-CX110-110-KIT and will see how fast they run.

I would like to run some videos which were encoded at 30-50mbps and these absolutely do not run over wifi no matter what the wifi is. Even "5 gigabit" wifi doesn't keep up, though probably because the 5Gb signal is usually so weak that normal 2.4Gb wifi runs faster ;)

Obviously, use a faster converter..the 100mbps one.

the cable guys do network over 75 ohm cable.

if you can use one coax for up and one for down all you need is the right baluns at each end, the balun trnsformers are going to need to pass

5 to 70Mhz at about about 80mW power. (you need the 5Mhz capability for the neotiation of fast ethrnet which uses faster symbol rate.

transforming 100 to 75 ohms calls for a turns ratio of 2:sqrt(3)

so a 7:6 ratio is pretty good.. The transfomers in a VGA to twisted pair adaptor might work, VGA is 75 ohms and SXGA is about 150HHz pixel rate so there should be enough bandwidth at the high end.

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  When I tried casting out nines I made a hash of it.

at 100Mbit/s (100 Base Tx) one pair the signal outwards and another carries the inwards signal, and the other 4 conductiors do nothing at all.

So you just need to interface the twisted pair tp the coaxial in such a way that the signal integrity is maintained. that where balun transformers come in.

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  When I tried casting out nines I made a hash of it.

Ok, this is not MoCA but it will likely work just as well. You will find that such solutions much better than WiFi.

MoCA has the advantage that it uses a radio band outside the normal cable bands so you can run cable TV and network at the same time over the same cable. When that is not required, a converter like you have chosen should work just as well.

The original coax ethernet is only 10 Mbps. Some hardware for that standard may still be in junkboxes or found as surplus, although a converter between coax and UTP was never common. There were hubs that had coax and UTP ports, however.

Today, proprietary converters exist that put 100 Mbps ethernet on coax, made for the video surveillance camera world where old coax-connected cameras are being replaced by IP cameras, and it can be attractive to re-use the existing wiring, especially for outdoor cameras.

Sorry if this a little off-topic, but has anyone here tried to run WIFI over coaxial cable in a point-to-point configuration?

Presumably, a coax not rated for 2.4 GHz will add a lot of attenuation, but WIFI devices were originally intended to communicate over the radio waves, where the attenuation between transmitter and receiver could be much higher. So the coax should still look like good connection that can offer multipath-free and nearly reflection-free signal integrity.

A spare WIFI access point and a spare WIFI client box with an external antenna connection each, a pair of attenuators and a pair of resistive

50 to 75 Ohm matching pads and some cables should be all it takes...

Are there technical reasons why this will not work (even with a pair of attenuators to match the transmitted signal levels to the receivers) or is the idea just too unconventional? I haven't seen it done so far.

Regards, Dimitrij

That should work fine. Don't worry about the impedance matching as

50 and 75 ohms are near enough to make negligible difference and any reflections in the cable will almost certainly be damped enough by the cable loss. Make sure you attenuate enough. The receivers will not want to see more than about -40dBm and the transmitters could be emitting around +25dBm. So you should have at least 65dB attenuation in total, including cable losses which you can probably look up or estimate from the data for similar diameter and construction cables. Split the attenuation roughly equally between both ends.

I have used a 15m long ultra low-loss coax (about 15mm diameter) with an antenna at each end to re-radiate WiFi to an underground location. It worked fine as long as the antenna at one end was a few cm away from the base station and the device at the other end was within a few metres of the far antenna.

John

Yes, I used that before the MoCA thing on the coax line that we had. It worked, but not nearly as good as the MoCA.

The WiFi used was the wellknown WRT54G and of course that was only a 54Mbps WiFi (which, as known, at most achieves half of that rate), so a lot slower than the MoCA which can run 100 or 400 Mbps fullduplex.

Also, as we pushed a lot of data over it we had frequent issues where the WRT54G hung up and had to be rebooted, which never happened once it was replaced by MoCA.

In our case the attenuation was so much that we just connected the WiFi routers straight to the coax and the received signal level was such (I don't remember exact values) that it was strong enough but certainly not too strong. When your cable run is short you will need to add an attenuator.

Rob wrote

I can report that I get 80-90 mbits/sec over 75 ohm video cable, using the above. That's pretty good.