Instructables

Ultra-cheap cell phone antenna

These are plans for an external cellphone antenna made from a wire hanger. The original writeup is at http://www.geocities.com/robert_maria/
 
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Step 1:

Can You Hear Me Now?Background
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.
Getting Started
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)
Construction
- 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.
Tuning
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 robert@watkins.net
Disclaimer
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.
VidDroog3 years ago
Say Not-Bob, or fellow commentors,

Are the external antenna jacks on the cell phones that are so equipped, some sort of standard?.. If so, what type of jack fits...?

On Palm Treo 700WX, it appears to be an unthreaded brass nub about 3.5mm outside diameter with a central "pin" hole approx 1mm; in a plastic plug capped recess, at the rear base of the antenna stub. The brass nub has a couple mm elevation from the bottom of the hole, with about 1mm clearance from the recess walls.

Looks like it would just about receive or mate with the male outlet (exposed pin and recessed space) of my computer's wifi card anntenna jack (and not using the external threads that the antenna cable uses).... in other words appears that it may be related to the standard RP-SMA (?) antenna cable connectors (except w/o the thread & nut portion)?
not-bob (author)  VidDroog3 years ago
That sounds like many of the external antenna jacks that I've seen, though I'm a bit surprised that a new-ish phone has such a jack. My best suggestion is to see if someone sells an adapter for an external antenna. Palm may sell one or an online retailer such as Wilson electronics may http://www.wilsonelectronics.com/.

Also, check your owner's manual for any tips they have for connecting an external antenna.

Best of luck!
hey.. im using d nokia 5310 and thers no place to plug in an external antenna... what can i do to connect it with my phone ???
not-bob (author)  waynebraganza3 years ago
Unfortunately, there's nothing simple to do. Today's phones typically have a shared antenna for each of the signals the phone may transmit/receive (cell/wifi/gps/bluetooth/fm/etc) This results in not having a port available. The options left are:
1) Get a cell signal booster that works with your phone
2) Get a new phone
3) put your phone at the focal point of a small satellite dish and use a remote earpiece/microphone (or bluetooth)
4) Tear into your phone and look for the antenna (I wouldn't suggest this unless you are willing to lose the ability to use the phone)

Each of these may be more or less appropriate based on your needs and available resources.

Good luck!
vtsnaab4 years ago
The sites posted here all seem to be gone now but this info is at:

http://robert.watkins.net/phone/

I only wish I lived less than 10 miles from any reception - my phone is just a paperweight when I am at home...there's more than just a mountain in the way !
not-bob (author)  vtsnaab4 years ago
Thanks for the clarification on the website. 

There are signal boosters that run $200+ that may be able to help with your reception. 
bluefly12155 years ago
this is right off the web page you posted. http://www.geocities.com/robert_maria/
better instructions there. but still not sure how to attach it to my phone.
not-bob (author)  bluefly12155 years ago
My short response is that likely you won't be able to if your phone was built in the last 18 months or so. With the advent of phones with bluetooth, wifi, gps, etc, the antenna technology has had to change to allow these multiple radio signals to properly send/receive. The result is likely that the vast majority of phone antennas that have been built support these multiple frequencies. Even if your phone doesn't have these features, your antenna has changed along with it. The kicker is that the reception has improved enough and people are much less likely to actually hook up an external antenna, that the ability to hook up an external antenna has been removed. Given all this, you likely have these scenarios. - look for a passive signal booster (these run $200- as much as you want to spend) - crack open your phone (at your own risk...) and figure out where to hook it up. - find a phone that has a jack for an external antenna Good luck
Dr.Bill not-bob5 years ago
There is another way.
Dr.Bill Dr.Bill5 years ago
Inductive coupling with a small air coil taped to the back of the phone where the antenna is inside the phone.
Dr.Bill Dr.Bill5 years ago
Go With The Force Luke.
N3ZJY6 years ago
What if this could be rigged as a "passive" repeater. I have aluminum siding, plus when the leaves come out in the spring my bars drop. So if the beam could be aim out of the attic window at the nearest tower and the coax attached to another beam or simply an omnidirectional, could that work?
amariusd6 years ago
If I'm not mistaken- most of the newer antenna amplifiers use some sort of dispersal antenna within the area the signal is going to be used i.e. room, vehicle, etc... so you don't have to plug directly into your phone. I'm not that good with electronics, but I'm sure someone who is could rig that up!
not-bob (author)  amariusd6 years ago
You're right. There are lots of amps that do this. If you have any luck with one, post a link! Thanks,
recon5066 years ago
I'm sorry, but this is not an Instructable. Your concepts are good, however I suggest that you split this up into steps, and use spell check. A little grammatical correction here and there wouldn't hurt either. Again, I'm not criticizing your ideas or projects, but rather the presentation of the aforementioned.
not-bob (author)  recon5066 years ago
I agree that the layout is lacking. If I remember correctly, the site changed since this was originally posted and the layout suffered. I haven't taken the time to correct. As far as the grammar, all I can say is "Good Catch!". Any specific suggestions that caught your eye that improves the ability to understand would be helpful. Thanks for taking the time to respond.
doo da do6 years ago
I ran across a web site last year, if I remember correctly I did a google on (cell phone towers) and a map came up, after you put in you zip code, this could really help in the (where is the nearest tower part)
rownhunt6 years ago
Can u use this for a walkie talkie if not can u post a link of a diy walkie talkie antenna??
not-bob (author)  rownhunt6 years ago
I wouldn't expect this to work for a walkie talkie since the antenna is directly tied to the frequency used. Here's how I would suggest you proceed: - find the frequency of the walkie talkie in question - find some yagi antenna design software (yagimax comes to mind) - re-calculate the antenna for the new frequency - Build it :) This is essentially the steps I did from someone else's design. Good Luck!
GEOD9986 years ago
WHAT DO U DO IF UR FONE HAS NO XTERNAL ANTENNA JACK???? CAN U STICK IT IN THE ANTENNA HOLE???
not-bob (author)  GEOD9986 years ago
If you have a removable antenna, it's likely that you will see some improvement. While I cannot guarantee what results you will see, I can offer some suggested experiments. - do not connect the shielding wire to the internal wire - take the internal wire and connect it to the metal portion of the phone where the antenna screws in. Good luck!
rusty_nail7 years ago
Nice yagi Antenna would be great for that cabin that you have thats just outside the coverage area should be good for 30-40 mile range have you tested the range what kind of DB gain would you have. One thing I would change is the Boom I would use PVC pipe maybe 1 inch diameter. This would be a great antenna for Camping or Deer Camp just turn off the ringer. Another quick tip is by adding a Plastic Wood working clamp it would make installing the antenna quick and easy for camping or to use in a temporary use but if on a cabin I would use a better mount. Also turn the antenna on its side for the best range cell towers are horizontally polarized. Great Ideal for that extra range
vtsnaab7 years ago
The author sent me a reference to his source article, and frankly I had totally
forgotten that RF does not behave as DC/AC do, so thanks.

More info here:
http://oldweb.clarc.org/Articles/uhf.htm

vtsnaab
vtsnaab7 years ago
This is poorly documented and would confuse anyone. WTH does this actually mean ? "- 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." I have used and soldered coax many times - but NEVER has it been correct to attach both conductors to the same element of anything, this would create a short circuit ! I will be happy when the source info is once again available because I live in a cellular dead spot, so if I can get ANY reception by making a more permanent version of this YAGI antenna with uncoated wire and a dowel, to mount up high, I would be delighted ! vtsnaab
Pongo72 vtsnaab7 years ago
You're totally wrong. This is a standard J-pole style configuration, used to provide a matching impedance to the coax without a transformer/balun. For your info, loop antennas are also a dc short(and usually have a 300 ohm impedance). Do not confuse rf impedance with basic dc electricity. In fact, this basic design dates back to few years ago. I remember seeing it in 73 magazine probably 15 years ago.
kandh077 years ago
Why can't we all just use metric???
PSPerson8 years ago
No offence, but this is kinda.........wierd
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