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Parabolic Template Frequently Asked Questions

Q: Does this thing really work?

A: Sure it works. This “thing” is just a miniature parabolic dish. It is designed using the standard formulas for generating parabolic shapes. This type of reflector has been in use for longer than radio has been in use. You see, reflecting telescopes work by using parabolic mirrors. So do some solar powered grills and ovens. It would seem that this reflector wasn't a “real” antenna. It seems just too easy. Surely a commercial antenna would be a better choice? Probably not actually, it depends upon what you are trying to accomplish. For applications where you just want more range indoors, you probably can't find a more effective solution that takes the form of an antenna. Sure you could buy an AMP, and it might prove to be a better solution, or not. The bottom line is this thing is so simple and effective that I suggest you try it and if you feel you can do better with a commercial antenna, go get one after you try this, then send me email with a comparison ;).

Q: How much gain can I expect with this reflector?

A: That depends upon many factors.

The approximate maximum gains for a few reflectors are shown here:
 

Frequency

6  inch Reflector

9 inch Reflector

12 inch Reflector

900 MHz

6 dBi

7.5 dBi

9 dBi

2.4 GHz (WiFi 802.11b)

12 dBi

14 dBi

16 dBi

5.8 GHz

16 dBi

20 dBi

24 dBi

* THESE NUMBERS ARE APPROXIMATE MAXIMUMS.  If you observe these kinds of gains, you got really lucky.

Q: Will this reflector hurt my hardware?
A: NO.

Q: Can I use two of these on my access point if it has two antennas?
A: Sure, I do it all the time.  Actually it is better to use two on access points which have two antennas.

Q: Will it work better if I use two of these on my access point instead of using only one and turning off the other antenna?
A: Yes, definitely.  Your access point is designed with two antennas because it works better with two antennas.  The vendor is using "spatial diversity" to decide which antenna the client is best heard on.  Diversity still works when you add two reflectors to your access point.

Q: Will it help to use a reflector at my client node as well (I have a WET-11 or similar hardware)?
A: Absolutely, but you may not always be able to measure the improvement.  There comes a point of diminishing returns.  Once you have a good signal it is difficult (with inexpensive systems) to measure changes in signal quality. Some antennas are not dipoles, the WET-11 is a case in point. It requires a different parabolic curve. There is a template for that curve on this site.

Q: How much will my range increase with a reflector?
A: That depends upon what your range is to start with.  Some people say, "WiFi is a three wall solution." If your current range limit is three walls and you use a six inch reflector, you will likely see another 2 or three walls of range.  If your current range is 800 feet and you use a six inch reflector, you will likely see your range increase to 1600 to 2000 feet.  There are many factors which affect this range estimation.  Strict line-of-sight is the only way one can say with reasonable certainty how much range will improve.  Strict line-of-sight, is not just being able to see the remote antenna, but also requires clearance around the path the radio wave takes to travel between the antennas.  Generally at shorter ranges (less than half a mile) you can say you have strict line of sight if you can see the other antenna.  The indoor range estimation problem is different, and has more to do with what is between the client and the access point and what other reflectors are on the premises.  Indoor range estimation is more of an art than a science.  Certain substances can be particularly tedious.  To name only a few; brick, cinder block, metalized insulation, thick plaster, metal screens, metal foils and mylar used to tint windows, etc.  Generally these frequencies will pass through most glass with little problem.

Q: Why did you make this design, what purpose did you have in mind for it, specifically?
A:  In one sentence,  "to improve the overall security of wireless networks operated by laymen."  I was installing access points on a local campus and wanted something that would let me limit the signal the access points transmitted outside the limits of the campus.  As I worked upon that problem, it occurred to me that any solution to that problem could improve the overall security of my country and my countrymen, if it were simple enough to implement.  These little reflectors are the result of that effort and are excellent for that purpose. 

I have been watching the state of wireless security for some while (three decades, if you count my time in signals intelligence) and have observed users (in communications parlance, operators) nearly always believe, "It can't happen to me."  It is quite difficult to impress operators with the importance of employing every security method at their disposal.  Operators nearly always fail to appreciat the true range of their equipment.  Many consumers believe that their signal goes no further than the garage because they can't get a link that far themselves.  They have not been educated to the idea that establishing a link requires two way communications, but intercepting traffic only requires one way communication. They do not realize that intercept can generally be done from twice the functional communications range of their equipment and often many times further. This situation continues today with the advent of 802.11b installations and is made worse by the consumer grade nature of the equipment and the average consumer's profound lack of understanding of the true worth of the information flowing on his wireless network.  I designed this reflector to be simple to implement because I believe the use of any directional antenna is better than the use of no directional antenna where security is involved.  I designed this antenna because anyone can build it and install it.  Understanding this reflector is easier than understanding MAC filtering or WEP or many of the other weird acronyms associated with 802.11b and it is my hope that many people apply this additional layer of security to their home networks.  It is a way for me to contribute to the health and security of wireless networks.  Remember, don't transmit into areas where you do not need to communicate.

Q:  I added an amplifier (WSB11) to my access point.  I have a good link.  Why should I consider using this reflector?
A:  The addition of an amplifier to your access point will increase the range all around the access point. Usually that is not the most desirable behavior because as you increase the range at which your access point can be heard, you also increase the threat of intercept, spoofing, and the sensitivity to interference.  With some amplifier units, the transmit signal is amplified but the receive signal is not amplified.  In such situations amplification will give you the ability to "talk" further than you can "hear".  A directional antenna can increase the "sensitivity" of your access point's "hearing".  The prudent thing to do when you add amplification to your access points is to also add directional antennas so that you :

Q: Can a pringles can be made into a reflector?

A: I have never spoken to anyone who has used a pringles can to make the reflecting part that has not been delighted with the results. Don't make the supporting parts out of pringles can material, though.

Q: Can I use this design with other frequencies, say my cellular service, or my 900 Mhz telephone's base station.

A: Absolutely! That is why I did NOT design in a dipole to drive the reflector, one of the reasons anyway. You see the driving element, the dipole is frequency dependant but the reflector is NOT frequency dependant. Pretty cool, huh? There is a guy in Australia who was using it with his cellular service, but I think he's moved from it to a Yagi. Yagi-Uda arrays are generally better at lower frequencies. They get hard to make at higher frequencies and parabolics become more efficient in terms of “bang for the buck”. These reflectors work at any frequency. Don't believe it? Ok, after you've made your reflector, go into a darkened room with it and shin a light on it then go look closely at the dipole. All the light is reflected towards the dipole. There is a nice picture of that in the gallery, someone did with strobe photography. Bottom line, works as designed, no matter what frequency you are operating upon. You just need to realize that gain is less at lower bands and more at higher bands.

NOTE:  This document is a work in progress.  I field questions via E-Mail and add them to this FAQ as they seem appropriate.  I can be reached via E-Mail for comment or questions here .