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Old 01-29-2009, 04:26 PM
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Default How to link antenna to wifi card?

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Old 01-29-2009, 07:24 PM
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On the reflector plate at the back of the antenna will be either a N type or SMA type co-axial plug. Check - it could be either male or female.

To this plug you connect a coax cable which has on the antenna end the oppite gender plug of the same type (e.g. if the antenna has a N type female plug, you want an N type male on the one end of the coax).

On the other end of the coax, you are almost certly going to have to put an SMA type coax plug - as almost all routers/modems and wireless cards which have coax plugs on them have SMA type plugs

... and again, make certain you get the gender right e.g. if the modem/router/wireless card has a male type SMA plug on it, make sure you have or get, a female type SMA for the coax.

Also:

- make sure you choose 50ohm type coax cable (not 75ohm).
- for simplicity sake, if you do not need to run more than about 10' of coax cable, I would suggest you get RG58 type coax cable - which is easy to connect to SMA type plugs - and if you cannot solder, then ensure the coax plugs are crimp type coax plugs and not solder type SMA coax plugs.

Does this all help you choose the right bits 'n pieces?

male plugs: a pin in the centre - and (obviously) female plugs: a hole in the centre.

Er ..... just why have you chosen this type of antenna?
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Old 01-29-2009, 08:19 PM
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Old 01-29-2009, 08:21 PM
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Quote:
Originally Posted by RFPOWER View Post
Does this all help you choose the right bits 'n pieces?
Yes and a great explanation!
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Old 01-30-2009, 08:14 AM
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Fair enough - but a couple points about the helical antenna: you get conventional mode and you get axial mode helical antennas - so take note as follows.

1) its only helicals in axial mode that will give you extended transmission and reception distances - and make sure that they are either both right hand twists to the helix coil, or both left hand tesists to the helix coil. if one is left hand and the other is right hand, you will loose approx 50% of the signal strength.

2) as for multi - path reflection reception you really need to use the helical in conventional mode - not axial mode.

3) any LNA connected to a card will fry it? Not true. Just make sure you choose an LNA that does not exceed the cards max db or dbi input, and if it does, purchase an in-line attenuator of the corrrect attenuation. I see where this is going, and quite frankly in this case you are going to be better off not with attentuation of any LNA, but with a higher gain receive antenna, and if that isn;t any good, then adding filtering - consider a low band pass filter with a steep roll-off (they are not cheap!).

Start talking about attenuators and LNA's and you are getting into the realms of lots of money, and a whole bunch of tecnical issues that are usualy well beyond the tech scope of the average DIY'er to assess correctly and accurately.

My advise (unless you are a tec geek) - KISS Keep It Simple Stupid.
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Old 02-07-2009, 04:40 PM
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Old 02-08-2009, 10:44 AM
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Use pvc tubing and then carry out all your antenna calaculations as if you were constructing the helical for a centtre frequency exactly 33% higher e.g. if 2437Mhz is your actaul centre frequncy (a good centre freq for 2,4Ghz WiFi, then build the antenna as if you are constructing a helical coil for 2437Mhz + 812Mhz = 3249 Mhz

... its all about the dielectric constant of PVC (also known as the permitivity of PVC)
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Old 02-08-2009, 04:06 PM
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That is a helical antenna, it works when its pointed to another helical antenna. Its not going to do you much good if the access point is an omni antenna. Consider the time it will take to build your DIY antenna, and not knowing if its correctly tuned...you really are better off just spending $40 for a 19 dBi BBQ grid form factor grid antenna.

I really doubt Radio Shack would have anything you need.
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Old 02-08-2009, 04:22 PM
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Nevtexjustin raises a valid point I should have mentioned - you are going to loose approx 3dB of your signal strength using a ciruclar polarised antenna (your helical antenna) to connect to a linear polarised antenna. You will loose about 3dB - that is about 50% of the signal strength.

In simple terms - unless you are going to be able to achive a real-world genuine 9db - 12db gain with your homemade helical, the benefits over using a vertically polarised grid, or even a high gain pro type omni directional antenna, are going to be next to nothing - to nothing.

... so you want your helical to give you a genuine 9db - 12db gain - not a theoretical - and without been able to measure your helical VSWR, impendance match and a couple other factors with instrument presicion (not just theoretical calc accuracy), getting that 9dB - 12dB will be very unlikely luck.

Note - any figure you see as db versus dbi - the differance between the 2 in the absence of any defineation can be taken as roughly 3. Keep that in mind when doing your calc's on paper.
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Old 02-16-2009, 10:42 PM
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Old 03-06-2009, 01:45 AM
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^bump^
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