Consult your local rural area, usually a farm with smelly cows, in search of the dish antennas used to transmit wireless cable TV service. Not the satellite dishes (DSS, DBS, Primestar, whatever they're called), those are for the wrong frequencies. You want the parabolic mesh dishes, Yagi , or corner reflector type antennas used for the 2.5 - 2.686 GHz, 31 channel MMDS/ITFS band. Get the physically largest antenna you can find, as these will have the highest gain, 24 dBi typically. They should be in relatively good shape as the antenna will be the most important, and weakest, aspect of your network.
Even though MMDS style dish antennas are made for the 2.5 GHz frequency range, they work fine in the 2.4 - 2.4835 GHz region used for wireless networking. There will be a slight loss of gain though. Dishes for the MDS (2.150 - 2.162 and 2.5 - 2.686 GHz, 33 channel) wireless cable service will also work.
Here are some quick notes about the parabolic type dish antennas you might find. The actual antenna is a normal half wave dipole with an integrated balun and is located inside the sealed plastic cover. The mesh screen is the reflector which concentrates the RF energy onto the antenna. That is how dish antennas increase the received or transmitted power level. Also, wireless cable service providers frown upon giving away their used dishes as they think you're going to steal cable service.
If their owner is not using them (switched to cheaper satellite service), they will usually give them to you for free. The dish will most likely have about a half meter of RG-8U with a N connector plug going into a sealed aluminum box mounted on the supporting mast, this is the downconverter, and is not needed, but take it, and its power cube if you can.
Picture of some parabolic dish antenna parts
Clean up your dish by scraping off all the dirt and rust with a wire brush or steel wool. You may have to resort to a Dremel tool to grid rust away if it's located in any hard to reach gaps. Try to get the reflector screen as smooth as possible, and straighten out any bent elements in the screen. Also, drill out any rusted rivots on the dish, if there are any, and replace them with stainless steel hardware. I first gave the dish a nice coat of Plasti-Kote clear top coat spray to fill in all the gaps along the screen mesh, and to provide a nice painting foundation. I then applied a heavy coat of flat black spray paint to the entire screen surface, along with the antenna and mounting brackets. Flat black paint will help it retain heat and melt any snow or ice build up, plus make it look hella cool.
Picture of a completed Lance 24 dBi parabolic dish. Total parts cost was under $10.
Upclose picture of the stainless steel hardware used to replace the rivots.
Picture of the painted antenna cover and small reflector.
Side picture of the dish antenna.
View of mounting bracket. Note the electrical tape to protect the coax.
Closeup of the painted antenna cover and small reflector.
Next, cut off the antenna's supplied N plug, and about a 30 centimeters of the antenna's RG-8U. The factory installed connector is low quality and the coax is most likely water damaged. Install a high quality N jack in place of the connector you just removed on the end of antenna's remaining coax. You must use the right size N connector (RG-8U most likely) on the antenna's coax for a proper installation. Be sure to do a very good job installing and weatherproofing the connector. Use coax seal around the connector gaps, and wrap a heavy layer of electrical tape around the base of the connector and some of the coax. You may also want to clean up and waterproof the square aluminum tube that connects the antenna to the reflector, as bugs tend to live inside it. The Great Stuff brand of expanding foam will work for this.
If you really want to, you can cut open the plastic antenna cover, remove the old RG-8 coax and solder your LMR-400 directly to the dipole antenna. This will give you a much better solder and mechanical connection than the original antenna bad, which is pretty bad. Make sure you keep all the brass strip possitions exactly as they were originally. If you do resolder the coax to the antenna, be sure to use a very small amount of solder. Solder is a very poor conductor, especially at microwave frequencies. Make sure the connection is as physically strong as possible then solder (with silver solder) the connection. Remove any excess solder with solder wick or by scraping it off. Also, be sure that when you put it all back together that you completely waterproof the outside of the cover using silicon sealant and paint.
If you're really nuts about preformance you can even sand down the plastic waterproof covering that surrounds the antenna. This will improve the overall gain by a few tenths of a dB.
If you have an extra parabolic dish, try making a cool parabolic microphone.
MMDS Antenna Pictures
- Lance Industries 24 dBi Dish Ahh...
- Lance Industries 3 foot Full Parabolic Dish Hmm...
- California Amplifier 21 dB QLP Parabolic Antenna Ohh...
- California Amplifier 21 dB QLP Parabolic Antenna Closeup
- Various Pieces of Hardware Used to Mount the Antennas
- Closeup of California Amplifier 22 Element Yagi
- Parts Diagram for the California Amplifier 22 Element Yagi
- Specifications for Lance Industries MMDS Antennas Some data for the antennas we use.
- Lance Industries Large supplier of wireless cable dishes.
- California Amplifier Large supplier of wireless cable dishes. Antenna specs online.
- Antenna King Large supplier of MMDS antennas
What If You Can't Find Used MMDS Antennas?
If you live in an area that is not serviced by MMDS wireless cable, you are most likely going to need to order some commercial 2.4 GHz antennas. Commercial providers like to jack up the price of their antennas because they know people (i.e. clueless ISPs) will pay obscene prices, but you don't have to! Take a look at these YDI directional antennas. Why, these $150 antennas are the same California Amplifier style antennas we get out of a dumpster for free! The best place to order small quantities of 2.4 GHz antennas for the hobbyist is Down East Microwave, Directive Systems ($80), Pacific Wireless ($75) or R. Myers Communications ($70)
It is even possible to salvage old PrimeStar dish antennas for use on 2.4 GHz wireless networking equipment.
Antenna gain can be approximated by counting the total number of elements and then using this formula: 10 log (number of elements). Example, a 22-element Yagi has an approximate gain of 13.4 dBd. This applies to omni-directional antennas also. A 18 dBd omni-directional antenna would need 64 sections. Parabolic antenna gain can be found using this design utility.
Here are a few homebrew antenna ideas:
- Tonic Wireless - Extensive Homebrew Antenna Website
- Homebrew 2.4 GHz Antennas
- A Simple 2.4 GHz Colinear Antenna
- A Simple Tin Can Microwave Antenna
- A "Cheap & Easy" 2.4 GHz Feed
- Do-it-Yourself 2.4 GHz WLAN Antenna
- Easy Homebrew 2.4 GHz Omni Antenna
- Deep Dish Cylindrical Parabolic Template Really neat antenna design
- Ez-10 10 dBi Corner Reflector Template
- Do-It-Yourself Wireless Antenna Update and Resource Center