It all started with my Nokia Communicator and my dad. My dad lives in a rural part of Oklahoma where the cell signal in the house is bad. He made a decision last year to get rid of the land line and only use the cell phones for him and mom. He bought a trucker cell phone booster online, installed it on the roof of the house and attached it to the phone and went from 0-1 bars to 5 bars. This, combined with a bluetooth headset, roughly gave him the same functionality as a cordless phone.
But then there was the Nokia. I've had it about 2 years and loved it. I use the past tense because it's dead. Or at least, mostly dead. The alarms for weekly meetings still go off, but the screen is all white and I can't make or take calls. I thought that I was getting a bad phone signal when I moved to a new house recently, so I tried to see if there were any plans to make an external cell phone antenna so I wouldn't have to shell out the $70 my Dad did.
I read some books from the library, downloaded a few programs and most importantly, ran across this article (I should appologize at this point to the author, Kent Britain, if I misrepresent his article in any way). It provided information to help me come up with an ultra-cheap design of my own that performs acceptably well.
You'll need the following materials:
A wire pants hanger
A length of coax cable (2' should do)
A plug that fits into your phone's external antenna jack on your phone. (or be prepared to rig something together)
You'll need the following tools:
A cutting tool for cutting the hanger wire
A drill or awl for the cardboard portion of the hangar
A ruler with 1/16" increments
A soldering iron and solder
A pen / pencil
A sharp knife (or coax cable stripper)
- Disassemble the hangar.
The wire will be used for the antenna elements and the cardboard tube will be used as the base on which to mount the elements.
- Cut the following lengths of wire (except the DE at this time) and lablel them:
R = 3 1/8"
DE = 2 7/8" (remember, don't cut this one yet)
D1= 2 13/16"
D2 = 2 3/4"
D3 = 2 3/4"
D4 = 2 11/16"
D5 = 2 5/8"
D6 = 2 5/8"
D7 = 2 9/16"
The piece DE (aka Driven Element for you Antenna designers out there) is going to be"J" shaped. The length of the top half will be 2 7/8" and the bottom half will be 1 7/16" and the distance between the top and bottom will be 1/2".
- Mark the cardboard tube:
Along each side of the cardboard tube,draw two lines running the length of the cardboard tube. Make them roughly opposite ends of the tube from each other. The spacing isn't critical, this will just help make the elements come out in a parallel plane.
Mark the following spots from one end of the cardboard tube on each of the lines drawn previously.
R = 1/2 "
DE = 1 11/16"
D1 = 2 7/16"
D2 = 3 3/8"
D3 = 5"
D4 = 6 11/16"
D5 = 9 3/16"
D6 = 11 11/16"
D7 = 14 5/16"
- Drill holes in the cardboard tube.
At each of the marks on both sides of the cardboard tube. The tube is hollow, so be careful to go through only one side at a time.
- Insert the elements into their respective holes.
- Prepare the coax.
There are usually five layers to coax cables. The outer plastic cover, a braided set of wires. Under the braided wires is a tin-foil thick covering of metal. This covers a thick plastic section with a thick copper wire in the center. If you are using a spare cable with coax connectors on both ends, cut one end off.
Carefully cut away the outer plastic cover about 3/4" from the end of the coax of an end of the coax with no connector.
Unbraid the wires that are showing and gather them on one side. Unwrap the metal and gather it with the unbraided wires and twist the whole thing together.
Cut through the thick plastic center being careful not to cut the center wire.
- Attach the coax to the cardboard tube.
Put the end you just prepared near the DE element and tape it in place. This will help with soldering.
- Solder the coax to the driven element.
It doesn't matter whether the center wire or the braided wire is put on top. Just put one at the center of the top and the other just below it.
- Attach the coax to the phone
If you didn't buy a plug, you will want to fabricate a plug of some sort. If you're lucky, you have a phone where it's obvious where the leads go, but some have a plug with multiple leads and you would have to do some research to find which ones to use.
This is a directional antenna, so you'll have to figure out which direction works best. My dad knew the general direction of the nearest antenna, so there wasn't much guessing. If you're not sure, pick a random direction and wait 10-15 seconds to see if a better signal is registered. My dad's phone took about 30-45 seconds to get to 4 bars. If you don't see any results, turn 45 degrees and wait again. Odds are, you should be able to figure out the optimal direction in just a couple minutes.
If I haven't been clear in any of my steps, you can contact me at firstname.lastname@example.org
This design isn't necessarily optimal and I'm sure someone will find a better design. If so, please publish it and share it with as many people as you can.