Homemade Airport Extreme Antenna

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catmistake's picture
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I really have no idea how antennas work. But I was inspired to try something today, and I'd like to see if someone can give me more information, or a place to look (I really don't want to pay $70-$100 for a proper antenna).

My girlfriend's iBook was having trouble with airport reception (turns out, jiggling the antenna connector for the card fixed that) so I somehow put 3 things together.

cell phone antenna adapter cable
cell phone car antenna
Airport card antenna from a G5

I ripped apart the G5 airport card antenna to get the MC-card connector out of it (I don't know how many of these things I've come accross... but if I ever get a G5 and need one, I am pretty sure they are cheap).

I jerry-rigged it to the adapter cable, which is connected to an older style cell phone car antenna (the one with a magnetic base, a spiral near the base of the antenna, which is slightly over a foot tall, bought for a quarter at a yard sale). I made sure the connection was tight between the MC-card connector and the adapter cable, all the proper metal pieces are touching. I hooked it up to the Airport Extreme's antenna port... set it about 8 feet away to give line of sight down a long hallway that my airport sometimes has trouble seeing around, well, mostly just all the way in the back room is where the signal gets flaky... I went back to test the signal... and... whammo! Absolutely no difference in signal strength.

I disconnected the antenna and plugged it into my cell phone to see if I got better reception. I did... from two bars without it to 4 with it... I tested it a couple times because I couldn't believe I was getting 4 bars (until today, I've never seen my cell phone give 4 bars way out in the country where I live).

I am nearly certain my cell provider uses freqs. in the GHz range... and so does the Airport...
So what gives? Assuming my connections were ok...why didn't this antenna work to give me better signal down a line of sight of about 35-40ft?

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Dr. Webster's picture
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Antennas need to match the fr

Antennas need to match the frequency range you're using. The higher the frequency range, the shorter the antenna. The fact that the cell-phone antenna didn't improve signal strengh shows that it's either too long or too short (probably the former).

You don't need to pay $70-100 for an antenna. Hawking Technology makes a good 802.11 omnidirectional antenna that will work with AirPort Extreme base stations for $30. They also make a directional antenna (which sounds like what you need) for a little bit more.

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There are several bands for c

There are several bands for cell phones, it depends if its analog, TDMA, or GSM. And there is different freq's used for each of those types.

Also, its not just a matter of antena length or diameter, its much more in depth of that. The only way your going to be able to tune the antenna is with a sprectum analyzer. And unless you want to dump a few grand on one of those, just go buy an antenna that is already setup for 802.11 that you are using. At work we have two Linksys WAP11's that are 200ft apart going across a HWY, they each have direction antennas going through windows from building to building and we get near perfect signal, even with lots of traffic going by.

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catmistake's picture
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cantenna

http://www.turnpoint.net/wireless/cantennahowto.html

I guess antennas are a bit complicated... but that thar is what I think I'm gonna do...

Although... somewhere here (I think?)
http://www.turnpoint.net/wireless/has.html

it warns not to aim the directional antenna at anyone, as it could be dangerous...

Anyone want to explain what that's about?

(btw... thanks for posting!)

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Well, that depends on the tra

Well, that depends on the transmit power. Lower power transcievers are noting to worry about.

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A [url=http://www.google.com/

A biquad antenna has quite nice gain and is much more compact. People have stuck them into sardine tins. Much smaller than a big ugly can. Wink

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catmistake's picture
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that does look nicer

and the double bipod gives more power...

my needs are basic, too...

just to get better signal in a room at the end of a 30-40ft narrow hallway.

I'm thinking the bipod style would be best, less of an eye sore.

I'm curous, would covering the top of the sardine cantenna with some kind of cotton or nylon mesh or fabric (to hide the element) affect its broadcast range/cause a fire hazard?

Is this a directional antenna? Can it be made to be one with a wider/deeper lip?

Also, any one know where I could get a MC-card (the connector for the antenna port on the Airport Extreme) already attached to a long (@20') cable of some quality? I found a site, but I think its in finnish or swedinsh... can't read that.

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I like the satelite dish mod-

I like the satelite dish mod- I've got two of those in the yard from previous owners, only problem is I only have a one story house and I don't think there's a chance in heck of getting line-of-sight to the public library and its free wireless access. Dang! For a brief moment I thought I could save $45 a month...

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Dr. Webster's picture
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Re: that does look nicer

catmistake wrote:

already attached to a long (@20') cable of some quality?

An antenna cable that long will negate any signal strength benefit the new antenna will provide. Keep the cable less than 3 feet long.

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Yeah, a 20ft cable is going t

Yeah, a 20ft cable is going to have a mass amount of rolloff. As you go higher in frequencies, the signal rolls off more. A long cable like that should only be used with low frequencies (VHF or lower).

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hopeing

That like with audio cableing, the thicker gauge of the cable, the better power at distance...

is this true?

Barry's picture
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cables

Go here, http://www.fab-corp.com They have the cables you need. Cell phone antenni do not operate in microwave frequencies.

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catmistake's picture
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one step ahead of you...

Funny, I was just on the phone with their customer rep. when I read your post.

They recommend, under the links on the left Cables >5 feet "Jumpers", and third down on the page, the LMR-400 NM/NM 25 Foot Jumper, which is 50Ω ($39.95)

and, under the links on the left, Cables <5 Feet "Pigtails", the 12 inch ORiNOCO/Avaya to N-Male Pigtail ($18.95)

I haven't even built the antenna yet

and I'd already be @ $55 overbudget...

The rep recommended a 50Ω cable, but what would be the problem with using a 20' regular ol' coax cable (like for cable TV, which I have already) which is 75Ω??

Thanks for the help everyone! Fritterers Rule!

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where's the rest of my post!

5 Feet "Pigtails", the 12 inch ORiNOCO/Avaya to N-Male Pigtail ($18.95)

I haven't even built the antenna yet

and I'd already be @ $55 overbudget...

The rep recommended a 50Ω cable, but what would be the problem with using a 20' regular ol' coax cable (like for cable TV, which I have already) which is 75Ω??

Thanks for the help everyone! Fritterers Rule!

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You will loose all your signa

You will loose all your signal in the first 2 or 3 feet of cable tv coax.

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catmistake's picture
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and this is because...

What's the deal... do you have a reason? I'm not even sure what question you are answering... please explain!

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You need to understand that *

You need to understand that *broadcasting* a signal is different than *receiving* one. The way stereos can use a length of speaker wire for an FM antenna is because they have internal amplifiers to maximize received signal. On the other hand, FM radio stations don't just set a pair of Radio Shack bunny-ears on their roofs becuase they need to get the most bang for their buck. Sure, you can use a piece of tinfoil/cell phone antenna/serving spoon as an antenna and hook it to a length of TV coax cable, but you *won't* be efficiently using the output power from the base station. 802.11 antennas on the market are the way they are because they've been designed to be as efficient as possible. If making a high-power 802.11 antenna was as simple as tinfoil and coax cable, then why would commercially-made antennas exist?

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catmistake's picture
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then... what would you do?

Would anyone pay $40 for 25' of cable? Sounds kind of extreme.

I guess the answer I was looking for was less philosophical. I know there are some pretty technical fritterers out there (ahem... Dr. Bob?) that are generous with knowledge, and although I got an 'A' in first semester Physics, I kind of dropped out of second semester Physics (something about Maxwell House equations??!!). Any way... what I was hoping for was a simple answer to:

Why is 50Ω is so vastly different from 75Ω such that something that works on a 25' 50Ω cable would simply not work at all on a 20' 75Ω cable? (I have $40 riding on the line here).

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Re: and this is because...

catmistake wrote:

What's the deal... do you have a reason? I'm not even sure what question you are answering... please explain!

http://www.timesmicrowave.com/cgi-bin/calculate.pl
here you go! 802.11b/g is 2400MHz tv coax is rg-58, microwave cable is the lmr stuff.

So at 20' you will loose 5.0 db of signal.

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I would use one of these,

I would use one of these, http://flakey.info/antenna/omni/quarter/ with one of these, 8 inch Right Angle MCX Male to N-Female Pigtail from fab. It's basically what I have on one of mine at home. My base station is a regular graphite one but the idea is there.

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catmistake's picture
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ohhhh!!

Quote:

So at 20' you will loose 5.0 db of signal

I don't see RF cables listed, but the LMR-400 is, and it only looses 1.65db at 25' and is 68.3% efficient. Assuming an RF cable is similar in gauge to an RG58, at 20' the signal looses @5db, and is only 32% efficient....

I only need this thing to boost some power down a 40' hallway for surfing the internet... and the antenna is going to be built directional... used in line of sight... anyone think RF coax will work for internet speeds (the fastest I've seen is about 400KB/sec off the net in front of the Airport... usually much slower [to the server I get @3MB/s], I'd be happy for @30KB/s down the hallway from the bedroom)?

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I think you lose about half a

All the lmr cables are microwave. I think you lose about half a db of signal with every connection. Also lmr-400 is close to half an inch thick and not very flexible, min 8" bend radious.

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dankephoto's picture
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catmistake said:

Quote:

I really have no idea how antennas work.

Talk about an understatement! Laughing out loud

Forget the long cable, signal loss and $$$ expense say it's a waste.

Instead move the entire access point; cat5 and power cables are way cheaper than that fancy lmr cable, and you'll get a better signal in the end.

dan k

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Yeah, right!

Better to have 5 crappy cables running nilly willy than one...

better yet! I'll leave my AP where it is and just move my house 20 feet to the east!

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Is there a particular reason

Is there a particular reason you want to stick 20' of cable on the antenna? If you put a better antenna it should work better, period. The signal loss you get from such a long run of cable will likely negate any gains from a better antenna.

As an example, would you hook up a pair of cheap unshielded 24 gauage copper wires to your stereo speakers for a run of 20' and fully expect to have decent sound come out? If the stereo techs told you that anything in a 14 guage or better would limit signal loss and shielded cables would save interference, wouldn't you want to use the better cables? Would you be willing to hook up a pair of premium Polks to that skinny wire and think that they would sound great? You can get cheap on certain things, but the laws of electricity and physics don't let you get very cheap when dealing with high frequency signalling.

Why don't you try just building an antenna and using a short ( < 3' ) pigtail and seeing if that helps reception.

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re: Yeah, right!

Ok ok, so if a big move of the AP isn't practical, then how about a small move. Sometimes just shifting it a few feet from its original position will improve the reception.

Another thing to try, and very cheap and simple too . . . put a metallic panel behind the AP to reflect the signal toward where you need better reception. Panel must be made of something that can reflect a microwave signal, steel, aluminum, brass, titanium Tongue whatever.

Even a piece of cardboard covered with Al foil would work. Doesn't need to big, .5 M square is more than enough. You can even give a bit of curve if you want focus it more tightly. Here's an example made from an opened-out Pringle's can.

If you must build/buy an antenna, Jon's comments are on the mark. Just add the new antenna right at the AP and point it in the direction where you need the coverage.

While I too know little about antennas and radio waves, one thing I have learned and do know - don't bother with very long cables, any useful 2.4gHz signal will die in a very short cable length. This mantra is repeated in everything I've read on this subject. Just because a 20ft cable is available doesn't mean it's the right solution for you. You need to keep the cabling as absolutely short as possible for the modification to have any value.

dan k

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Thanks for the suggestions.

Frankly, I don't understand why my reception isn't better than it is without an external antenna. These frequencies should move through walls, right? and the range is supposed to be 50' radius for 56Mbit, and 150' for 11Mbit... I shouldn't even need an antenna.
I don't have a cordless phone, I rarely use the microwave, and if I am I'm not using the computer anyway...

In this room I've been talking about, my bedroom (@40' away), I get flaky signal. Its the same on my other wireless computers. The walls here are cheap and thin, and the layout of the whole house is something like 70' X 12', and the airport is about 15 feet off the far wall. I'm in the middle of no where, there are no power lines running through here, other than the one that runs to the house on the other side of my bedroom. I'm not running any kind of encryption, and I've tried it both with Interference Robustness and without...

I don't really want to spend the money on an antenna, nor do I want to move the Airport (I can shift it around a little, maybe hang it on the wall above where it sits).

The only thing I can think that may be causing interference is that it sits about a foot and a half above an old harmon-kardon amplifier, and that sits about a foot above my switch and towers.

The TV is rarely on, just did that for the pic, those monitors are always off, and the SE/30 is off unless someone wants to access it...

What do you think? Is this just a problem with electrical interference? Or did I get a bum Airport? What happens to an Airports performance as it gets older anyway? Does it get less powerful?

You all are kind for offering suggestions and ideas.

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Depending on what the walls a

Depending on what the walls are made of or what's in them, no the signal won't go thru. The airport extremes don't have the best signal to begin with, that's why they made an external antenna for them. At 40' you should be getting some signal though. Try moving the startion up higher. Both of mine are way up by the ceiling.

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I suppose you could also just

I suppose you could also just get another airport base station and put it in another room.

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