how do i find out how much db my antenna is

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how do i find out how much db my antenna is

Postby TheSovereign » Thu Jul 25, 2002 8:17 pm

how would i measure this without complicated instruments

also how can i measure the interference i pickup and how do i clean it
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Postby Thorn » Thu Jul 25, 2002 8:40 pm

The simple (and NOT the most accurate) way is to get a reading using a card w/o an external antenna, and a AP or another card. Next plug in the antenna, and read the signal. Subtact the first reading from the second. The difference is the rough gain of the antenna. Don't forget that the readings tend to be in negative numbers since we're dealing with radio waves.

First reading: -90
Second reading: -75

-75 - -90 = 15. Diffenence is 15dB gain.

Hope this helps.
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Postby Thorn » Thu Jul 25, 2002 8:42 pm

Changing the questions while I'm answering... That adds a challenge. :)

What kind of interference are you experiencing?
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Postby lincomatic » Thu Jul 25, 2002 8:50 pm

if you're getting interference, it will probably show up as a higher noise figure. try changing channels from 1 to 6 to 11 (these are the only 3 non-overlapping channels) and see if the noise level goes down with any of them. hopefully, it's not wideband noise that would pollute all of the channels.

also, when measuring the gain of an antenna make sure you don't do it inside...the reflections from the walls will skew your readings quite a bit. the ideal setup is to have both the AP and card outside in an open area w/ less reflections, but if not, at least take the client machine outdoors.

which brings to mind yet another question for anyone who knows... what is a better indication of gain, increased SNR or increased signal. i've noticed that when i use a good antenna sometimes the SNR goes up more than the signal because the noise also goes down.
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Postby Thorn » Thu Jul 25, 2002 9:04 pm

SNR.

BTW, other pair of channels don't overlap. 1-6-11 are the only three that are exclusive to each other being used at the same time; but you can do other 2-channel combos if you have a need.

1 6 11
2 7
3 8
4 9
5 10
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Postby TheSovereign » Thu Jul 25, 2002 9:08 pm

actually i get mostly noise -100 and upwards of -175

my antenna isnt exactly to the scale the instructions gave me
i can pick up any ap in a about 1 block radius
but when i go to pickup a dhcp address i cant
i have to unplug the antenna and get upclose and personal
even thought the antenna is giving me all greens
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Postby Thorn » Thu Jul 25, 2002 9:22 pm

Originally posted by TheSovereign
<snip> my antenna isnt exactly to the scale the instructions gave me <snip>


First, Dimensions are CRITCAL at these frequencies. Get everything as close to the correct sizes as possible. Even 0.1" can be signifcant in this range.

Second, experiment using a good known AP. Trying to get something to work if you have no idea what's on the other end will only lead to frustration. Hell someone could have a tried a tinfoil antenna on the AP for all you know.

Third, there are legal dangers to getting a IP via DHCP if you're not invited. Be careful, you may be on thin ice.
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Postby TheSovereign » Thu Jul 25, 2002 9:31 pm

im taking the canadian stand on hacking satillite tv
they are freely transmitting it to you
as long as you dont tress pass do what the system will allow u
if u wanna give me cancer your gonna pay for it with my television shows and free internet
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Postby TheSovereign » Fri Jul 26, 2002 11:16 pm

ok i made the necesary changes to my antenna to fit scale and i measured it at about 12db is that normal for such a small antenna? or is this a false reading

the antenna is just a 8 gauge coil .75 CM in diameter that has 28 turns then at 1.75" the second coil has 25 turns then back into the ground connect
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Postby lincomatic » Fri Jul 26, 2002 11:33 pm

Originally posted by TheSovereign
ok i made the necesary changes to my antenna to fit scale and i measured it at about 12db is that normal for such a small antenna? or is this a false reading

the antenna is just a 8 gauge coil .75 CM in diameter that has 28 turns then at 1.75" the second coil has 25 turns then back into the ground connect


sounds too high to me. where did you get this design?
i'm a little confused about your description. is this what it looks like?

---signal--28 turns---25 turns--ground
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Postby TheSovereign » Sat Jul 27, 2002 1:08 am

this is what its supposed to look like
i got the instructions from a friend of mine in arizona he deals with high frequency wireless
he says this is the best type of antenna for its size
it recieves transmissions sideways so its meant to lie down flat
u can add more sections of turns as long as u alternate from 28 to 25 and back

.75 cm is the size of the turns i found a screw driver that was exactly .75 cm
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Postby lincomatic » Sat Jul 27, 2002 1:17 am

interesting. i've never seen anything like that. could you ask your friend where he got a weird design like that?
the purple lines on the bottom...rh bend and to ground...dimensions critical at all? and how about the coils...what spacing?
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Postby Thunderforge » Sat Jul 27, 2002 3:54 am

Originally posted by TheSovereign
as long as you dont tress pass do what the system will allow u


If your machine is requesting an IP address from their DHCP you ARE tresspassing as you are now putting something on their network, you are no longer just picking up what they freely transmit to you.
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Postby TheSovereign » Sat Jul 27, 2002 5:20 am

the dimensions are very important except the gauge of wire im using something alot thinner. i think im using gauge 16.
the coils must be 1.75 inchs apart according to him.
ill take a pic of what i got, its pretty simple but when i plug it in my snr shoots up.

purple lines represent uncoiled copper wire.
the silver thing at the bottom is the lead coming from the orinoco card and ground is the outer ring of the orinoco card so u DONT actually ground it your connecting it to your pcmcia's ground

i had made it a little smaller to fit inside a pcmcia case
and i was picking up all kinds of interference.
when i made the appropriate changes i can connect a whole lot easier.


thats not what i meant by do what the system will allow
i mean use whats available to you
yeah i been caught a couple times and more times then not they just want to know how u did it and how they can stop it and i tell them. i take my stumbling rig everywhere i go.

its a libretto 50ct with an orinoco silver and the antenna i just put a picture of
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Postby mentat » Sat Jul 27, 2002 6:02 am

I believe lincomatic was asking what the spacing was between individual turns was, not between the sets of coils.
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