Question for the Hams

[peterh]

Here's a question for our radio-knowledgeable members.

I'm going to install a WiFi bridge unit in our trailer and place a WiFi antenna on the roof. It's a 30cm, 10dB antenna and the WiFi bridge unit will be sitting almost right underneath it on the other side of the fiberglass shell and Reflectix insulation. To further boost my reception I'm going to build a parabolic reflector made from 1/4" hardware mesh that I can slide down over the antenna and point toward the campground access point to boost my incoming and focus my outbound signal.

Will adding a ground-plane -- something like aluminum foil glued to the underside of the shell and grounded to the outer conductor of the antenna lead -- under the antenna improve my reception and range? How large a ground-plane do I need?

[Ken C]

Im thinking i would not ground it to the metal material since it wont be a resonant Counterpoise type of ground plane... the length won't matter. But the larger the surface area to reflect the signal the better. example, like a metal car roof with a mag mount antenna on top of it. Others more smart than me will have better help for you though.

[peterh]

Ken, if that's correct will the aluminum-Mylar skin of the Reflectix insulation work as my ground plane? (That would be too easy!)

[Curtis F.]

It's not that simple. If you are going to add a parbolic reflector, that is all you need for a ground plane. A Google search for "wifi antenna improvements" generates many ways to improve signal reception. Everything from a metal strainer to a satellite dish. The closer the reflector is to parabolic the better it will focus the received signal on the antenna.

Curt

[Steve L.]

Wouldn't a parabolic reflector be highly directional? I would think that by and large omni directional would be preferable??

[Ken C]

I’m thinking off the top of my head the antenna from the factory is already tuned and resonate. If you ground it to the material you have no idea if you messed all that up or not without getting an antenna analyzer. I would just use the Reflectix for the reflecting of the signal. I know a gentleman who did this with a custom made truck camper. He had refelctix type material built into the roof for his ham antennas up there. It wasn’t grounded to the antennas, but was just the same principle of a mag mount antenna works best on top of a car roof as opposed to sitting on the bare earth/ground. The material reflecting the signal but not a resonant part of a tuned system. Other smarter hams will chime in here I may have it all wrong. take care.

[Terry G]

Curtis is right. A parabolic reflector doesn't need a ground plane. But I don't understand trying to make one out of hardware cloth because there's a lot of inexpensive ones available online and they'll probably be more effective than a do-it-yourself. I think you should also invest in an inexpensive WiFi signal strength meter. This will make it a lot easier setting up your antenna at the campground.

[Darwin Maring]

Save time and money and look at this site:
http://www.cyberguys.com/product-search/?k...rd=wifi+antenna

I have the item number 2020164 and it works great.

[Orlen Wolf]

Peter

First of all I think that the antenna you are describing will do just fine as a stand alone antenna without any additional hardware.

A ground plane is not necessary since the antenna is a collinear stack of dipoles, probably center fed, commonly referred to as an elevated feedpoint antenna. It is possible to boost reception in a favored direction with some type of parasitic element but I don't think you will get enough of an increase to warrant the effort. A reflector or director rod would be your best bet if you want to experiment. You could also look into a corner reflector or trough reflector. They are much easier and more forgiving to build than a parabolic reflector. Remember that you are also adding the complexity of having to rotate the antenna and reflector/director to peak the incoming signal.

We did a lot of field testing of WiFi antennas for a system that is designed to cover 8,000 sq. mi. and require multiple data relays. We found that, overall, it was better to just use omnidirectional antennas. Introducing any type of directivity in the system created more problems than it cured. It also meant we would have to aim about 4,500 *&^$#! antennas.

BTW - 10dB over what reference? dBi, dBd, dB over a wet noodle in a copper cage? I've found that manufactures claims on WiFi antennas are more in the realm of fiction or fairy tales than data from engineering tests.

Here is a picture of one of our field test setups. The antenna shown was advertised as a 15dBi omnidirectional antenna and was about 1 meter overall length. It tested out at just under 10dBi. The 50cm antennas were advertised as 7 dBi and tested out at just under 6 dBi.

[peterh]

Thanks to all for your comments and advice!

Answering some of the questions & comments:

Steve: Most -- hopefully all -- of the time I'm hoping my big omni-directional WiFi antenna will do the trick. Its size will pull down more signal than a stock unit and, by sticking it on the roof of my trailer I'm hoping it'll get the best possible sight-line to a campground transmitter.

Problem is many campgrounds use cheap-cheap-cheap little WiFi routers with stubby little antennas that aren't nearly as good at pulling in a signal. Adding a parabolic reflector should help focus my outbound signal on the cheap antenna so it can hear my signal better. The hard part, as Orlen points out, is gettng the reflector pointing the right way. A few degrees off and you get nada. It's a tricky business.

Which is why I'm making a reflector thatis easily removed or installed. I'll slide it down over the antenna and point it in the right direction when all else fails. It's an experiment.

Terry: A reflector made out of 1/4" mesh won't catch the wind, which would knock the reflector out of alignment.

Darwin: My setup will be the same kind of thing, except I'm using a router that'll allow us to connect two (or more) laptops to our "access point." The router itself will use "open source" software that'll allow me to monitor signal strength and tune my antenna position.

Orlen: I was hoping you'd pop in. I am not an antenna expert, and your comments are much appreciated!

I have no clue how accurate the vendor literature for the antenna I bought is. I've seen comparable antennas advertized for 9, 10, and 14dBi. Chances are the marketing materials are overly opimistic and it's actual performance is much less, but it should be a big improvement over the 10cm antenna the router came with. I'm hoping that, by tripling my antenna size and optimizing its location (on the roof outside our Reflectix-aluminum-Mylar-sheilded trailer) will be enough, but some campground signals are so weak . . .

The design I picked up on is a simple 11" wide parabolic trough. Easy to build and easy to point with no verticle orientation. I picked 11" because it's compact and the parabolic curve I'm using for making a plywood former will fit on a single piece of printer paper.

Why I'm spending time on this right now when I'm already swamped I'm not really sure. I'll post pics and results when I (eventally) get this thing up and working sometime this summer.

[David Morgan]

[Terry G]

Carrier but no signal--a little radio humor.

[Paul Braun]

Why not purchase something made for that exact purpose. You have all the proper connectors, it can be insulated, it can be grounded, I do not like reinventing the wheel. You want a directional antenna, I have found the best choices come from Hawking Technologies.

What sort of computer are you using or will you install a router in bridge mode?