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Author Topic: DIY wifi boosting. Wifi antennae from sat cable ? Antenna design. Reflectors.  (Read 13632 times)

setecio

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From this video http://www.metacafe.com/watch/837885/wifi_antenna_hack it suggests an easy way to make a more powerful wifi antenna. I have some Satellite grade CT100 coax cable and wondered if I could make a simple wifi antenna from this in the same way a coat hanger can be put in a TV ? I don't know the theory of how wifi antennaes work, so if anyone knows, please let me know.

My thoughts were to cut 12 inches of the cable, cut off 11 inches of everything to leave only the inside copper core wire, and then follow the video to make the coil, screw on a connector on the remaining 1 inch of insulator and connect to the wifi PCI card antenna connection.

I don't have all the parts right now but will try when I source them. I'm just wondering if any wifi antenna expert out there can offer their views of this suggestion, especially whether what I do with the the remaining 1 inch of insulation / shielding braid/copper foil/ dielectric matters ? (In sat cable the shield becomes grounded through the connector)

Is there any circuitry or components in the base of the antenna or is it really just a piece of copper wire plugged into the PCI card antenna input ?

Thanks.
« Last Edit: February 16, 2008, 11:25:41 PM by setecio »
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soms

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Re: Wifi antennae from sat cable ?
« Reply #1 on: February 16, 2008, 03:48:56 PM »

Hmm all I know about radio antennas is that the bigger the antenna wire and the greater the earth the better reception you get.

With normal radio equipment if you hold the lead on your radio you are providing a better earth than that of the equipment and so the reception improves.

The video is interesting as it looks to be basically the same thing - increasing the length and size of the antenna cable to extend range.

I dont know how anything about radio or Wifi but would think it is more sensitive to what it picks up. I think the number of coils has something to do with the operating frequency as well so to few or to many may affect performance.

I dont know about how to approach it with CT100 cable but would be tempted to try it myself as I have a spare cheapo PCI card with antenna somewhere I could take apart and play with.

*Edit*

Please realise I know so little about radio in general so if you think I am wrong please tell me  ::)
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setecio

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Re: Wifi antennae from sat cable ?
« Reply #2 on: February 16, 2008, 03:58:25 PM »

On another forum, I enquired about connecting the antenna input on the PCI card to the copper central heating pipes, as this would run all around the house (what an antenna  :lol: ) but was told that earthing a wifi antena is not good for it .... but I don't know anything about wifi antennas and I don't know if that person did either.

I wonder if the antenna input on a wifi PCI card is grounded ?

(If you are going to try, you could first try plugging the wire directly into the input if your antenna unscrews, as this would save permanently altering the antenna.)

Will be interested to hear your finding, if you try.  (and any others)

If a wifi antenna is just copper wire, then a really cheap antenna would be to solder some wire into one of these (eg for Netgear with SMA connector)
http://cgi.ebay.co.uk/2,SMA-Right-Angle-Elbow-Male-to-Female-Coax-Adapter,18_W0QQitemZ220201430865QQcmdZViewItem
« Last Edit: February 16, 2008, 04:03:27 PM by setecio »
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roseway

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Re: Wifi antennae from sat cable ?
« Reply #3 on: February 16, 2008, 04:08:27 PM »

It's not entirely right to say that bigger is better. A longer aerial will collect more signal, but if its length is wrong for the signal frequency then the actual signal level going to the equipment will be reduced. Aerials for very high frequencies like this need to be tuned to match the frequency for best efficiency, and this is what the extra coil in the big aerial achieves.

To answer setecio's question, I don't think there's any sort of earth involved in this type of aerial. If you wanted to place the aerial some distance from the equipment you would have to use appropriate co-ax with the braiding earthed, but with the aerial connected directly to the equipment only the inner connector is used. It is, as you say, just a piece of copper wire connected to the antenna input.
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  Eric

setecio

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Re: Wifi antennae from sat cable ?
« Reply #4 on: February 16, 2008, 05:34:32 PM »

Aerials for very high frequencies like this need to be tuned to match the frequency for best efficiency, and this is what the extra coil in the big aerial achieves.

I'd be interested in more info about the coils in the extended antenna. The guy in the video has just copied the number of coils in a bought version. I'm looking at my CT100 cable which has a nice dialectric (plastic) section once the outer insulation and braid is stripped away.

I'm wondering how much effect do these coils have ? If a 10 inch antenna with coils has an 8db gain and a 10 inch without coils has a 7db gain then I wouldn't bother with them and would leave the dielectric.

However if the coils make a massive difference in gain or if without them destroys some component of the signal, then they will be necessary.

The guy in the video has just copied what he found, but do you know how great is the need for coils and if it is a negligible benefit or an essential requirement ?

Thanks.
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guest

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Re: Wifi antennae from sat cable ?
« Reply #5 on: February 16, 2008, 06:01:05 PM »

Your antenna needs to be the right length which can be determined by :

λ = c/f where λ = wavelength, c = speed of light and f = frequency

If you put the figures in for 802.11b/g wi-fi then you'll find that the wavelength is between 12 and 12.5cm so a suitable value for λ would be 12.25cm. Normally for an omnidirectional antenna you would design a quarter-wave dipole so the length of the antenna element would be 3cm or so. Make the antenna element shorter and it'll work better at the top-end of the band (channel 11/12/13); make it longer and it'll work better at the bottom end of the band (channel 1/2/3).

The coils are what increases the gain of the antenna element and 3dB in this case is a doubling of signal strength as we are dealing with power and not voltage. Edit - I wouldn't have thought that only one antenna element would produce a 3dB increase in signal strength. I'd have thought you'd need multiple vertical elements (it's called a collinear antenna) to manage this on an omni  :-\ Edit - it is of course a collinear antenna as it's 2 quarter-wave dipoles with a meander coil in between :doh:

The main question to ask is what sort of antenna does the wi-fi equipment have now?

Edit to correct stupidity :P

Edit again - I have a set of jpgs with dimensions for a four element collinear somewhere. God knows where they came from but I'll dig them out if you want?
« Last Edit: February 16, 2008, 06:14:44 PM by rizla »
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setecio

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Re: Wifi antennae from sat cable ?
« Reply #6 on: February 16, 2008, 08:46:42 PM »

Thanks but I think the jpgs will be beyond my understanding.

These type are commonly sold as about 9db gain
http://www.solwise.co.uk/wireless-indoorantenna-omni-9osc.htm


I think that is what was used in the video.

Maybe DIY reflectors might be a better route to take
http://www.freeantennas.com/projects/template2/index.html looks a neat one offering 9db gain  ???

There are loads of different versions out there
http://www.usbwifi.orcon.net.nz/


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dave.m

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Re: Wifi antennae from sat cable ?
« Reply #7 on: February 16, 2008, 09:52:23 PM »

Regarding your question about connecting to the central heating pipes, this is what I posted in reply:

It might work in theory BUT, all pipes should be earthed so if any electrical equipment develops a fault or any short circuit occurs in your property you could end up with a live current up your copper pipe.
Even for a couple of milliseconds I don't think it would do your wifi a lot of good.
  :no: :no:

There are more technical and safer ways of doing what you want.  :D
dave
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roseway

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Re: Wifi antennae from sat cable ?
« Reply #8 on: February 16, 2008, 10:07:33 PM »

Central heating pipes must be earthed according to the wiring regs, so they would be quite useless as a big aerial.
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  Eric

setecio

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Re: Wifi antennae from sat cable ?
« Reply #9 on: February 16, 2008, 10:46:16 PM »

Thanks dave, yes it was that and Derek's reply "Somehow, I doubt whether connecting your aerial to earthed pipes would prove to give any worthwhile gain. "

Apart from the electrical risk, is it that the signal just drains away to earth ?

Just found the quickest and cheapest reflector for antennaes using empties.
http://www.youtube.com/watch?v=Vv3Tr04IKn4

I see it is not a parabola but if it is quick .....
I wonder if it works, and what beer cans give the best signal  :drink:   ;)

The problem is it'll take a few cans to get the design perfected, but by then my design concentration might be affected  :drink:
I'll just have to keep trying and hopefully get it right before  :vomit:
Maybe I'll just stick with Coke cans.  ;D

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guest

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Re: Wifi antennae from sat cable ?
« Reply #10 on: February 16, 2008, 10:49:33 PM »

What exactly are you trying to achieve?

Obviously it's "boost the signal strength" but in what direction - up, down, all around (omnidirectional) or narrow-beam ?

If you explain where the access point/router is and what direction you'd like the signal strength boosted then that'd help quite a bit :)

Edit - ah cantennas :)

Try http://www.lincomatic.com/wireless/homebrewant.html for some ideas.
« Last Edit: February 16, 2008, 10:51:40 PM by rizla »
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setecio

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Re: Wifi antennae from sat cable ?
« Reply #11 on: February 16, 2008, 11:15:34 PM »

What exactly are you trying to achieve?

Started off thinking I could use my left over CT100 cable to make a better antenna for my neighbour's wifi, but now just having a general chit chat about any ways of DIYfi boosting.

Thanks for that link, excellent details on it with measurements too  ;D I've been through dozens of pages on google, and that is the best by far for details  ;D

Nice details for the collinear http://www.lincomatic.com/wireless/collinear.html
 :silly: looks pretty effective :
Antenna                SNR
ORiNOCO built-in: 10 dB
collinear:               20 dB
« Last Edit: February 16, 2008, 11:22:50 PM by setecio »
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Ezzer

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Try looking up any thing on the net refered to as a "CANTENNA"

there are a few show me how vid's avalable via you tube one I once found (and if i do again i post the link) is by a few amatuer wannabe diy presenters. It's worth watching for the entertainment value alone, When I saw it i resembled a certain icon to a spooky degree  :lol:

A lot of them are baised on making an antenna using a pringles container although many metalised tube with a metalised base one end can also work.  Essentualy the're based on a Yagi antenna with a balanced sheild around it to make it very directional with a very high gain. I may try making one shortly, if so I'll let every one know how i get on

Otherwise to boost the range from the router I've seen the following a few times and all the users seem very happy with the performance

http://www.maplin.co.uk/module.aspx?ModuleNo=38205&doy=17m2
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Ezzer

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Found it.

Want to see how to make a cantenna, watch this  :hmm:

Want to have a really good laugh watch this any way (especialy if the terms Tool time or Binfords rings a bell) :clap2:

 http://www.youtube.com/watch?v=KN_1oe3z7EQ&feature=related
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smoo

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Re: Wifi antennae from sat cable ?
« Reply #14 on: November 22, 2008, 08:29:15 PM »

Maybe DIY reflectors might be a better route to take
http://www.freeantennas.com/projects/template2/index.html looks a neat one offering 9db gain  ???

Just to say I made one of these in about 10 mins and it worked a treat ;D

My mum can now pick up the signal from my sisters house across the road, about 30 metres
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