Help with Wifi antenna

Please see subject line-- Help, Wifi Antenna-- on alt.binaires.schematics.electronic for a picture of my concept. Looking to combine Helical antenna and Wifi adapter card in one unit. My experience is limited to MW bcb. I know there are many pitfalls at

2.4Ghz, so I'm looking for feedback on how to do this properly. I'm using the following page as my guide.
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This is to extend the range of my laptop computer.

Mike

Reply to
amdx
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Note that in almost all places there are legal limitations on EIRP (Effective Incident Radiated Power). In plain English, the more you narrow a signal, the stronger it becomes.

Since you did not say where you are, I'll mention the two places I know for sure. In the U.S. WiFi EIRP is limited to 1 watt for mobile/portable use (e.g. laptops) and 4 watts for fixed links.

With a 100mW source and a reasonablyshort cable the famous Pringles can antenna would be illegal for mobile/portable use and probably illegal for fixed links. It happened to be developed by an FBI agent in the process of an investigation, so he was covered, you may not be.

Here in Israel it is limited to 100mw EIRP, so unless you have a very long cable, any gain antenna would be illegal. Someone wrote up (in Hebrew) and posted on a web site his use of a similar antenna. It's not obvious to the casual reader that he did it in an area under the jursidiction of the IDF (Israeli Army) and got permission from them.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com  N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838 
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Reply to
Geoffrey S. Mendelson

Hi Mike

You sure find some great information on the Web.

I consider this article Jason Hecker publishes

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to be ALL the instructions anyone would need for constructing a 20 dB directivity WiFi antenna. I am looking for some feedback from you on its performance.

If you plan to investigate basic effects of changing size and shape of Helix antennas, EZNEC sure makes Helix antenna investigation easy.

I am just curious, what kind of coax and connectors are you using, and, ?how much coax?.

Jerry

Reply to
Jerry Martes

Bear in mind that 2.4GHz is also an amateur band where no erp limits exist!!

Jeff

Reply to
Jeff

Oh , really ?! cite!

Reply to
Allodoxaphobia

Only 802.11b/g channels 1-6 fall in the amateur allocation of 2390-2450 MHz.

If operating under amateur regulations you must identify by CW, phone, RTTY or TV image every 10 minutes or less (see 47CFR97.119), your transmissions must be intended for reception by another licensed amateur station or station authorized to communicate with amateur stations (see

47CFR97.111), that has to be the only reasonable way to effectively communicate, no other radio service available that accomplishes the same communications (see 47CFR97.113) and you have to use the lowest power level capable of accomplishing the communications (see 47CFR97.313).

See

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for specific regulations.

Reply to
gwatts

I forgot to mention amateur communications cannot be encrypted, so no https, see 47CFR97.113 again.

Reply to
gwatts

Reply to
Barry Watzman

Most amateurs set the SSID of the access point to their call sign, since this is beaconed numerous times per minute. Apparently that's close enough to RTTY to keep most people happy.

Sure.

This particular regulation creates plenty of argument, since realistically the vast majority of activity on amateur radio frequencies these days could be just as readily accomodated by either cell phones or the Internet; I doubt the FCC has cited anyone for violating this rule for decades now.

Indeed, although this too is subject to debate because people will argue that while, e.g., 1W will get them a bit error rate of 10%, they "need" a near-zero bit errorr rate and therefore transmit at 100W.

You point about not being able to use HTTPS or other encrypted protocols is probably the most significant change in moving from using WiFi in an unlicensed mode to using it under the amateur radio service's rules. However, note that it is perfectly OK to obfuscate *authentication* data such as passwords -- packet BBSes have done this for decades.

---Joel

Reply to
Joel Kolstad

Very few people would have significnat difficulty passing the technician class license exam that's needed to operate on 2.4GHz. Indeed, there are many month-long (meet a couple times a week) classes and even weekend "cram" classes that have near 100% success rates in getting people their tickets. A passing score is 80%!

Reply to
Joel Kolstad

Hi Jerry, Please review the picture I posted on alt.binaires.schematics.electronic in it you will see I'm trying to avoid connectors and cable carrying 2.4Ghz R.F. Thanks for being the only poster to have anything near a response to my post. Mike

Reply to
mike

"Jeff" wrote in news:46a784ab$0$1347$ snipped-for-privacy@reader.greatnowhere.com:

Not in most civilized countries.

2.4 Ghz is unlicensed, not unregulated.
Reply to
Gary Tait

Hams have a segment of it, but not 2.4 to 2.5.

However, if the wifi ends up in the ham band in a commercial purpose there will be hell to pay when they get caught, ham or not.

Reply to
Don Bowey

Well.. not all the 802.11b/g channels are in the amateur band, and even there, there is a power limit (transmitter output power, though, not EIRP), so you could conceivably fire up your 1500 Watt transmitter into a 20dBi antenna and blast away.

There is the other rule about minimum power needed for communication, though.

Reply to
Jim Lux

Do note that many people's Usenet servers do not carry any binaries groups, so they will be unable to look at your picture. If you were to place the photo on a server where it can be accessed by HTTP or FTP, these people would be able to get it. Many ISPs provide some web space served by their own web server, and there are free photo hosting sites like flickr.

Dave

Reply to
Dave Martindale

The Wifi Helical antenna is an awful lot of work, and the performance of even long structures on PVC tubing is vastly disappointing. The easiest 15 dBi (my measurement) gain antenna is the Biquad. In fact, if you make the biquad with circular instead of square loops, the construction is even easier, and there's no problem measuring with all those bends - - just one wavelength of straight wire in a circular loop for each section - -

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But try to keep a 50-ohm coaxial configuration all the way to the feed points as in
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It isn't necessary to keep the polyethylene insulation - - for a short length of air insulated coax, the tubing ID should be 2.25 times the center conductor OD for 50 ohms impedance.

If you are like me, you will probably want to build the Helical anyway - - just to see, and perhaps to compare against the two easiest wifi antennas with decent performance - Biquad and Waveguide

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The easiest waveguide can is the 83mm ID one you get with the 28oz size of Bush's Baked Beans or any of a number of other products like canned spaghetti sauce or family size Spaghettis.

See if you can get a USB Wi-Spy Spectrum Analyzer module, too - - try to find one of the original (no external antenna - - cheaper) versions, and just put it in your own shielding enclosure and make your own modification to cut the path to the built-in antenna so that you can run a small coax to a connector on the box for your own external antenna connection. This kind of modification has been made by others - -

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scroll down to the post by pe2er on 9/9/06 showing how to connect a coax to the board. I used a type N connector on my enclosure because it's universal and strong, and filtered the three USB supply and signal wires with feed-thru capacitors so no RF can enter the enclosure through these other paths. Use Metageek.'s Chanalyzer software to run the Wi-Spy module - - preferably version 2.0 before the current 2.1.4 came out, since the need for compatibility with both the $199 Wi-Spy and the $399 Wi-Spy made operation with the $199 Wi-Spy somewhat unsatisfactory. Maybe you can ask Metageek to allow access to previous Chanalyzer 2.0 for owners of the older units. Why do you want all this? So you can make accurate measurement of the differences between antennas, using a reference 1/2-wave dipole, or the standard RPSMA antenna you find on most Wifi Routers. The dB calibration of the Chanalyzer display is very accurate.

Chuck W6PKP

Reply to
Chuck Olson

FYI, alt.internet.wireless discusses this topic often.

I prefer the biquad antenna, which you can augment with a dish. I have a short-cut method to build this antenna. With a combination of these photographs and this link, you should be able to figure it out.

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Note you don't need to make the loop a square. Use a circle of the same circumference.

There is a disadvantage to using the helix. It will receive both horizontal and vertical polarization. Most sites just send in one polarization. In busy areas, the same channel will be used in different sites with different polarity. Now if you use the helix to illuminate a dish, then the circular polarization is fine and perhaps desirable. That is, you could sniff out signals without the attenuation associated with having the wrong polarization.

Reply to
miso

Hi Mike

My computer skills are really lacking. I dont know how to view your images. I do spend alot of time learning about antennas. One of my buddies tells me that he had poor results with the helix he built from the instructions you cited. This site seems to have been better for my buddy.

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Is it practical for you to use a Bridge at the input terminals of your gain antenna so that the coax loss is minimized? That way, the antenna (+Bridge) is connected to the computer with CAT 5 cable. If it isnt too complicated, tell me how to view your images.

Thanks Jerry

Reply to
Jerry Martes

But, I suppose that believing, as did an earlier poster: "Bear in mind that 2.4GHz is also an amateur band where no erp limits exist!!" is acceptable for these No-Code, No-Klew Licensees?

Reply to
Allodoxaphobia

Spaghettis should read Spaghettios

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Reply to
Chuck Olson

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