2.4ghz propagation on standard residential coax between houses

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Discussion Overview

The discussion revolves around the feasibility of transmitting 2.4GHz signals through standard 75-ohm CATV coaxial cable between adjacent houses. Participants explore the potential for using existing local cable networks for this purpose, considering factors such as signal attenuation, network architecture, and legal implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that while 75-ohm CATV coax is not ideal for 2.4GHz, they are curious about the distance signals might travel through the local cable network.
  • Another participant mentions that RG6 cable has an attenuation of about 7 to 10 dB per 100 ft at 2 GHz, referencing its use in home satellite TV systems.
  • A participant describes the local cable network's architecture, indicating that the main coax feed is converted to fiber optic at a node, limiting the coax's distance from the house.
  • One contributor expresses uncertainty about the presence of upstream filters that might attenuate signals and questions the impedance matching of 75-ohm RG6 with Wi-Fi cards.
  • Another participant asserts that upstream for Comcast ends at about 40 MHz and emphasizes that it is illegal to inject foreign signals into the network.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using coaxial cable for 2.4GHz transmission, with some suggesting it might be possible while others highlight significant limitations and legal concerns. No consensus is reached regarding the practicality of the proposed setup.

Contextual Notes

Participants mention various factors that could affect signal transmission, including attenuation rates, network architecture, and legal restrictions on tampering with cable networks. These factors remain unresolved in the discussion.

mastafoo
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I know 75ohm CATV coax is anything but ideal for 2.4GHz, but I am still curious as to how far these signals will travel upstream through the existing local cable network (splitters, etc) laid by the cable company, and if they could be transmitted between adjacent houses on a street. Example: an AP is connected directly via F connector to the coax line at one house and client at a nearby house connects to their coax, allowing Tx/Rx completely through the cable. Surely several hundred milliwatts should be able to push through.

Thanks
 
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The attenuation of RG6 cable at 2 GHz is about 7 or 10 dB per 100 ft if I remember correctly. These cables are used extensively for home satellite TV which works by taking a chunk of 1 GHz to 2 GHz IF signal from the LNB converter at the dish to the satellite receiver in the living room.

Edit:
And as far as the local cable network is concerned, the main coax feed which splits to houses in a neighborhood is converted to a fiber optic line at a node. It is the fiber optic that eventually makes its way to the cable company which could be many miles away. So the coax itself doesn't get very far from the house anyway.
 
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what said:
snip

Edit:
And as far as the local cable network is concerned, the main coax feed which splits to houses in a neighborhood is converted to a fiber optic line at a node. It is the fiber optic that eventually makes its way to the cable company which could be many miles away. So the coax itself doesn't get very far from the house anyway.

interesting... wonder where you live ? and how new the network is ?

I'm in Sydney , Australia and there are 2 maj cable networks by 2 of the maj comms companies. They ARE cable all the way from source to customer.

I don't bother with cable TV jst a waste of money, but I do get my phone and internet service over that cable network. I havent, as yet, discovered what the freq range is used for the network.

cheers
Dave
 
I subscribe to cable internet and TV (comcast), and have reason to believe that my node is shared between a hundred or so houses in the neighborhood. In that case I guess it could be possible to use this coax between the houses to send signals (802.11g or maybe video). I'm just not sure if there are any upstream filters or anything like that installed which would attenuate the signals, or if 75ohm rg6 will even match wifi cards' impedance
 
davenn said:
interesting... wonder where you live ? and how new the network is ?

I'm in Sydney , Australia and there are 2 maj cable networks by 2 of the maj comms companies. They ARE cable all the way from source to customer.
I don't bother with cable TV jst a waste of money, but I do get my phone and internet service over that cable network. I havent, as yet, discovered what the freq range is used for the network.

cheers
Dave

In the US, most of the major cable companies are running huge fiber optics networks to service large metropolitan areas. Those fiber optic cables begin at the headend and end at a node in some neighborhood (although there are some exceptions). The node is just a small box hanging at a pole, or could be accessed underground, where it converts the lightwave from a fiber into an RF cable signal between 50-850 MHz downstream, and 5-40 MHz upstream. The coax cable is then split multiple times and can service 500 to a few thousands customers at a time.

mastafoo said:
I subscribe to cable internet and TV (comcast), and have reason to believe that my node is shared between a hundred or so houses in the neighborhood. In that case I guess it could be possible to use this coax between the houses to send signals (802.11g or maybe video). I'm just not sure if there are any upstream filters or anything like that installed which would attenuate the signals, or if 75ohm rg6 will even match wifi cards' impedance

It's not possible to do that. Upsteam for Comcast ends at about 40 MHz, and it sure is filtered. And also, it's illegal to tamper with their networks by injecting a foreign signal into it.