Parabolic Template FAQ

Parabolic Template Frequently Asked Questions

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

A: That depends upon many factors.

The antenna supplied by the vendor. Usually it is a dipole. Most vendor supplied omni-directional antennas will work with this reflector. Usually you can't get a look at the vendor supplied antenna without voiding your warranty. The dipole supplied by the vendor may or may not be in the exact center of the plastic/rubber housing. This means that it is best to "tweak" your setup by moving the antenna around in an area about the size of a dime and centered upon the specified "focal point". This tweaking can make a significant difference.
The material from which you make the reflector. Solid reflectors of smooth metal are best. Often people make reflectors of cast off tin cans. These work fine but the ridges in the can may cause the reflector to "scatter" the reflection and cause the focal point to be fuzzy. This is more pronounced with smaller reflectors. Screening works well so long as the mesh of the screen is smaller than 1/4" at 2.4 GHz and 1/8" at 5.8 GHz. At 900 MHz you can use 1/2" mesh screening. A Pringles can may be cut up one side and flattened with a steam iron on low heat to prepare it for use as a reflector. It works just fine.
The care with which you make the reflector. This design is sensitive to errors. You should try to keep all measurements within 1/8" at 2.4 GHz and 1/16" at 5.8 GHz.

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 that have two antennae.

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.

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 for a middle school student to implement. These little reflectors are the result of that effort and are excellent for that purpose.

If you place your access point in one corner of your house, say in the basement, and point it up towards the center of the house, you will likely be able to get link to the access point from anywhere in the house but not from the street in front of the house, or from the next door neighbors house.
Placement of the access point in the basement or attic of the house and pointing the beam towards the center of the house can often limit the accessibility of the AP to only the local premises.
In my case, I managed to place three access points in a campus area 150m x 150m and at the same time limit accessibility to the physical premises of the campus. It took a high gain dish to even detect any of the access points from off campus. All access points were installed out of doors and with clear line of sight to much of the campus, else what would have been the point of installing them?

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 :

DO NOT cause interference to other nearby users of the spectrum.
DO reduce your area of coverage to confine it to your property and thus limit your exposure to hostile activity.
DO improve your coverage in areas where you desire the best possible coverage.

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 .