Hacker News Reader

Comment by jakedata | Hacker News Reader

For houses that have coaxial cable tv runs to many rooms it would be great to find a 75 ohm f-connector wi-fi antenna that you could just screw onto the wall plate. You would need to match impedance with the WiFI device at the other end but the result would be reasonable WiFI in whatever room you want while the ugly blinkenboxen remain in the basement. Rather than use splitters it would be best to use one cable per antenna. Something to ponder while staring at my basement parts bin for sure. edit: https://en.wikipedia.org/wiki/Wi-Fi_over_Coax

View on HN

Even ignoring the impedance mismatch, loss in typical 75 ohm coax at 2.4GHz is going to be something like 0.5dB per metre. Far worse again at 5GHz. That's going to add up quickly.

If nothing else is on the same run, the amount of noise from external sources should be very low, which in many noisy RF environments is fine when you are only going 10-20 meters through a building. The transmit power of a wifi card is going to be way above the amount of losses that would cause issues.

For comparison, to see if this matters, what's the loss through air?

The loss from air itself is a tiny fraction of a decibel per kilometer.

But using an antenna means you lose 40-48dB in the first meter for 2.4-5GHz. And then you lose 6dB for each doubling of distance, so another 12-18dB for 4-8 meters.

If you're less than 20 meters from an antenna, not only do you have those massive upfront losses, you still lose more than .5dB for each additional meter of distance.

Coax wins in almost every situation.

Every coax system in every house I've ever seen (in the US) has been a mishmash of cables and splitters of random length and quality, usually with unterminated branches.

That means absolutely horrid performance at RF frequencies. Cable TV is mostly okay with this poor quality, you can still get a picture from the bad signal, but it might be fuzzy or dark. I can't imagine wifi would work at all under those conditions. You'd get reflections with random phase offset, and it'd probably totally destroy the signal.

What you want is probably possible, but it would require a dedicated line to each terminal run back to a central location with no splitters. At that point, you're just running worse ethernet with extra steps.

Fortunately I am working on my home, not yours. I have RG6 quad shield home runs to lots of useful places but I didn't want to pop for MOCA bridges.

Reply on news.ycombinator.com