Making a Reflector

Overview

In Chapter 15, I described a range booster for Wi-Fi client adapters, made from a tin can and a gooseneck lamp base. It's proven extremely useful for getting my laptop connected from the far corners of my rambling ranch house, and even from inside our detached garage and way out back where my big telescope lives.

My Tin Can Bandwidth Expander got me connected to my access point at full speed, but it was really a fix for a problem with my access point: The shape of its microwave field is nothing even close to the shape of my house. Ideally, I'd like the access point to fill my house with its radio field, but not go outside the walls. (Well, outside some of the walls, and as far as my detached garage, heh.) This is a vain hope, since radio waves don't respect wood very much, and brick only a little more.

On the other hand, consider what I had: An access point with an omnidirectional antenna sitting in my upstairs office at one end of my long and crooked house. The full-speed region of the access point's field was going most of the way to my living room couch, but it was also extending quite a ways through my walls out into the driveway, where it was of no use (except perhaps to a drive-by hacker). Worse, the kitchen lay between my access point and my living room coffee table, and it cast a 'microwave shadow' due to the presence of large metallic things like the refrigerator, microwave oven, and cupboard full of canned goods and utensils. A rough sketch of the shape of the access point's field is shown in Figure 17.1. I've compressed the size of the house and simplified its shape, but the gist is there: The kitchen cast a shadow, leaving a 'dent' in the top-bitrate boundaries of the field right where the living room couch was.

Figure 17.1: The Effect of a Microwave Shadow.

Thus the shape of the microwave field within our house was almost optimally bad for connecting from the living room. My Tin Can Bandwidth Expander was a 'spot fix' for a misshapen microwave field. The real solution would be to reshape the field so that it fit the shape of our house a little better.

I played with a number of things, and the good news is that most of them worked. I put a gain antenna high up on the wall above my access point-and that worked. (The little rubber antennas that come with access points are optimized for low cost, not high effectiveness.) I could connect from the living room without the help of the Tin Can Bandwidth Expander. Unfortunately, it also extended the field another forty feet out past my driveway and as much as I like my neighbors I'm not necessarily into sharing my bandwidth with them or inviting them to peruse my home network.

I put a flat piece of sheet metal 18" x 24" behind the access point. This worked too, in that it changed the shape of the field and significantly reduced the extent to which the field excursed behind the access point, out into the driveway. It also changed the shape of the field inside the house, but mostly by moving the dead spots around. Signal strength in the living room came up some, but not radically.

What worked best for me came out of an idea I saw on the Web. A gentleman named Michael Erskine had done some work with parabolic reflectors made of 1/4' mesh hardware cloth, the same stuff you buy at Home Depot by the roll and use to keep the bunnies away from your roses out in the garden. Michael's Web site contains photos of how he used a mesh reflector with a Linksys USB Client Adapter to shape its field and extend its range, and built the whole thing into a tidy and unobtrusive plastic cylinder:

http://osiris.urbanna.net/antenna_designs/projects/template/index.html

Michael's geistesblitz provided me with a whole new approach, and eventually yielded a gadget that made the Tin Can Bandwidth Expander obsolete-at least from the living room. (I still need it to connect from out in the garage or in back by my telescope.)