Author Topic: Wifi directly over cohaxial cable  (Read 3970 times)

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Offline wolf32d

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Wifi directly over cohaxial cable
« on: February 14, 2015, 01:41:12 pm »
Hi fellow nerds!

Wifi cards max power output is about 15 or 20 dBm. Their max input power is usually -10 dBm. Now the question: if I bridge two wifi cards directly with some 50 Ohm coaxial cable with an attenuator in the middle (e.g. a lambda/4 stopband filter) will I pop the suckers or will they transmit data succesfully?
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Offline ConKbot

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Re: Wifi directly over cohaxial cable
« Reply #1 on: February 14, 2015, 01:51:49 pm »
I'd spring for a real attenuator, rather then trying to get a quarter wavelength stub to attenuate it precisely.  2, 30dB attenuators seem like a good starting point.  Any particular reason for wiring the wireless instead of using ethernet or the air?
 

Offline wolf32d

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Re: Wifi directly over cohaxial cable
« Reply #2 on: February 14, 2015, 01:59:42 pm »
Well I have an old pc in my lab which has a blown ethernet port and a crappy wifi card with exceptionally bad reception at 1m from the router... I just wanted to recycle this pile of garbage LOL  :)
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Offline NANDBlog

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Re: Wifi directly over cohaxial cable
« Reply #3 on: February 14, 2015, 02:05:47 pm »
Probably one of these USB dongles costs less than any attenuators or the coax cable itself.
 

Online SeanB

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Re: Wifi directly over cohaxial cable
« Reply #4 on: February 14, 2015, 02:07:05 pm »
Just use the cheapest junkiest coax you can find that can be made to fit the connectors both ends ( you might need to adapt each up to a F connector and use TV coax) and ther cable loss will do the job nicely with transmit power turned down at both ends. As a bonus you will still have Wifi reception within 5m of the cable.
 

Offline elgonzo

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Re: Wifi directly over cohaxial cable
« Reply #5 on: February 14, 2015, 02:12:26 pm »
You could just spend a few bucks (< EUR 5) to get yourself some arse-cheap ethernet card or Wifi USB adapter for your old PC. Should be much cheaper and less pain than tinkering around with the "Wifi" cable. (Unless you love tinkering... ;) )
 

Offline aveekbh

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Re: Wifi directly over cohaxial cable
« Reply #6 on: February 14, 2015, 03:04:03 pm »
Although the maximum rating is -10 dBm, you will usually not get good performance until -20 to -30 dBm (depending on the actual hardware). That could actually explain why you get poor performance close to the router.

A simple experiment that I will suggest - move the router away and see if performance actually improves. (I suppose moving the router may be easier than the PC). If you can't move it, try placing a sheet of aluminium foil between the PC and the router to increase the attenuation.

If you want to cable up the WiFi link, you need at least 40 dB, possibly 50 dB attenuators. For comparison, attenuation of coax cable (e.g., RG-316) is about 1-2 dB per metre at 2.4 GHz.
 

Offline G7PSK

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Re: Wifi directly over cohaxial cable
« Reply #7 on: February 14, 2015, 03:08:45 pm »
Cut your co ax and place the two pieces next to each other for a few CM. should be enough coupling.
 

Online wraper

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Re: Wifi directly over cohaxial cable
« Reply #8 on: February 14, 2015, 03:13:35 pm »
Although the maximum rating is -10 dBm, you will usually not get good performance until -20 to -30 dBm (depending on the actual hardware). That could actually explain why you get poor performance close to the router.
+1, I had a router and access point from the same manufacturer which did not work together at all if put closer than 1.5 meters. However they worked normally at 500m distance between them with external antennas.
 

Offline NiHaoMike

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Re: Wifi directly over cohaxial cable
« Reply #9 on: February 14, 2015, 05:00:12 pm »
Cryptocurrency has taught me to love math and at the same time be baffled by it.

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Offline Neganur

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Re: Wifi directly over cohaxial cable
« Reply #10 on: February 15, 2015, 11:33:42 am »
Well I have an old pc in my lab which has a blown ethernet port and a crappy wifi card with exceptionally bad reception at 1m from the router... I just wanted to recycle this pile of garbage LOL  :)

1m from the router is too close. I'd put an attenuator on the wifi card's antenna to see if that improves the situation. If it's an integrated one you're out of luck, even if you can decrease the output power via the driver, the base station still blasts the receiver.

Connecting two wifi cards together is not something I would do.
 

Online tggzzz

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Re: Wifi directly over cohaxial cable
« Reply #11 on: February 15, 2015, 12:40:40 pm »
Well I have an old pc in my lab which has a blown ethernet port and a crappy wifi card with exceptionally bad reception at 1m from the router... I just wanted to recycle this pile of garbage LOL  :)

1m from the router is too close. I'd put an attenuator on the wifi card's antenna to see if that improves the situation. If it's an integrated one you're out of luck, even if you can decrease the output power via the driver, the base station still blasts the receiver.

That close I'd try removing the antenna on the PC, or maybe replace it with a paperclip. All you need for attenuation is a really "suboptimal" antenna :)
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Offline rob77

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Re: Wifi directly over cohaxial cable
« Reply #12 on: February 15, 2015, 12:49:51 pm »
i think it's not the smartest idea of using a coax for wifi :D but if you'll do, then watch out for the power reflected back to the transmitter.. it might easily happen that you'll fry both transmit (reflected power) and receiving (too much input power on the receiving side) ;)
best way would be to buy a USB ethernet dongle or a USB wifi dongle to solve your situation.
 

Offline NiHaoMike

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Re: Wifi directly over cohaxial cable
« Reply #13 on: February 15, 2015, 04:10:06 pm »
You can try wrapping some black (conductive) ESD safe packaging materials around the antenna in order to make an attenuator.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

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