Is a antena Y adapter possible ??

Is a antena Y adapter possible ??

Postby hack6500 » Fri Sep 06, 2002 9:37 am

i like to think im like most people, but apparently i'm not.. you see i find myself scouting with my 5dbi omni and when i discover an AP i then disconnect the omni, and hunt down a better signal with my directional. this proves to be very useful for signal qual. yet the whole disconnect-reconnect ordeal takes precious seconds that i'd rather have planning my burn-out/getaway.

seriously, my idea would be a N-type Y adapter (so that i could use it with my various pigtails) with one Female adapter and 2 male adapters. Hopefully allowing me to have my Omni connected at the same time as my directional. yet i can find no google or ebay results on any such device, maybe im looking for something quite original?

Is such a device capable of working? has anyone made/bought/sold/tested something like this? am i smoking something other cigars? should i shave or wax my back hair?

thanks guys!!
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yes it's possible.

Postby mr_wlan » Fri Sep 06, 2002 11:11 am

u will need to build a wilkinson divider as you'll need to ensure the impedance is matched. personally, i'd use a vy good quality microwave relay to switch between antenna's. If you are good with electronics, then open your card, and add two antenna sockets in place of the two internal diversity antenna;s then do the switching in s/w.

regards,

mr_wlan
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Postby Firebird » Fri Sep 06, 2002 7:23 pm

great idea, i've wondered if that was possible. i thought of mounting two directionals at different heights or pointing in different directions but i'm sure there would be more loss and it would kill the whole setup
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Postby Entropy42 » Sat Sep 07, 2002 10:01 am

The antenna patterns will either interfere/compliment with each other.

You can use power dividers/combiners to create a phased array.

Examples:

Phased array of omnis to form a directional pattern. (Combining two omnis will give you gain, but it will no longer be an omnidirectional pattern.)

Phased array of yagis - 2x the signal (3 dB gain) if two yagis are fed in phase (equal lengths of coax from combiner/divider) and are side-by-side pointing in the same direction.
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Postby Sh00t3r » Sat Sep 07, 2002 10:06 am

yet the whole disconnect-reconnect ordeal takes precious seconds that i'd rather have planning my burn-out/getaway.


LOL, I had to do this last week after someone approached me in a parking lot.
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Postby Firebird » Sat Sep 07, 2002 6:30 pm

If a cop approaches your car just do what Peter Shipley did and pour a bottle of water on your shirt and explain that you pulled over to clean up safely.
;) ;) ;)
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Postby hack6500 » Mon Sep 09, 2002 6:57 am

i spent some time researching your ideas mr. wlan, and i would like to share some links i discovered and to ask a few more questions.

This page ( http://www.ee.bilkent.edu.tr/~microwave/programs/magnetic/mwpower/wilkinson.htm ) has a good depiction of what a wilkinson adapter really is, and for the application i intend to use it for i belive that i will want an "Equal Divider" .?.

Rember my application is 1) roof mag-mounted omni 3db antena 2) hand operated mini yagi directional antena both connected through the "Y adapter" into my pigtail-n-card. I would ultimately like to find details on how to build this device myself, and basicly at the lowest possible cost providing the best results. (isnt that always the case?)

A more detailed explanation of a Wilkinson Adapter was found in this document ( http://www.itee.uq.edu.au/~coms7302/module_6.pdf ). with more technical explanations and tests found in ( http://www.itee.uq.edu.au/~coms7302/Power%20Dividers.pdf ). While also here i discovered ( http://www.itee.uq.edu.au/~coms7302/Directional%20Couplers.pdf ) which beged the question, would this type of splitter work? as it looked easier to build.

That last link started my serach in another direction and i soon discovered ( http://rfwireless.rell.com/pdfs/AN_M561.pdf ) which might suggest that 180 degree hybrid would be good for the 2ghz and above range. This document ( http://www.linkmicrotek.com/pdfs/appnotes_4.pdf ) may back my idea up.

A little more googling turned up this site ( http://www.kditriangle.com/couplers.htm ) where they have such devices documented. I looked at the Hybrid Couplers, 3 dB 0º/180º MH Series ( http://www.kditriangle.com/pdfiles%5CMH.pdf ) for the hybrid approach. alternatively they also have a Directional Couplers, Type N CA-N Series ( http://www.kditriangle.com/pdfiles%5Cca-n.pdf ) available. I still havent gotten any prices on either of these though, any other info would help!

My job is not done! My question now is: Should i go with a 0º/180º Hybrid or a Directional Coupler ? Which would be safer/easier to build (probably the 0º/180º)?

Thanks for all your help people! most of these links are worth the read, i enjoyed them and im certianly not an EE.
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Postby Entropy42 » Mon Sep 09, 2002 7:42 am

Overkill.

A coaxial T and two quarter-wavelength 75-ohm coax transmission lines are all you need.

1/4 wave of 75-ohm coax will transform a 50-ohm impedance up to approx. 100 ohms. These are paralleled together at the T to get you back to about 50 ohms. (It's closer to 56 or so - Optimum value for the transformer coax is about 72 ohms. Close enough.)

Again, as I said - You will be SORELY disappointed if you try to combine a yagi and an omni in such a manner. The two antennas will interact in a manner that you won't expect, and the interaction will depend on all sorts of factors such as:
Relative phasing of the antennas (lenghs of the coax from the antenna to the T)
Position of the antennas relative to each other.
Orientation of the antennas relative to each other.

Combinations of antennas that make sense:
Omnis spaced 1/2 wave away fed in phase.
Omnis spaced 1/4 wave away fed 90 degrees out of phase
Yagis parallel to each other fed in phase. (Spacing of 1/2 wave or more.)

There are others, but a phased combination of a yagi and an omni is pretty rare. (Might be useful for killing yagi sidelobes, etc. But not any applications a stumbler would care about that I can think of.)
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phasing

Postby mr_wlan » Mon Sep 09, 2002 1:10 pm

yes, the previous post says it all. a couple of 1/4 wave lines etched in pcb will work, although you'll get some odd effects. you could use pin diodes at each 1/4 wave to switch the antennas but I think for your app, you want a microwave switch.

Or,

you could get a preamplified antenna, and use a receive only sniffer - that will save you trying to DF the AP with a yagi, and you wont be relying on trying to get the AP to hear your probe request packed from NS.

hope that helps..?

regards,

mr_wlan.
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