make a homemade antenna booster that will give you FULL BARS!! Read more: http://cellphoneforums.net/general-cell-phone-forum/t86490-make-homemade-antenna-booster-will-give-you-full-bars.html#ixzz27DULhW6P

Actually, that can work, if...

You make a dipol antenna at 1/2 or 1/4 wavelength out of foil -- better would be copper tho. Of course you'd have to know which GSM frequency your phone is using at the time, and need different size antennae for each frequency.

You could also build a wide-range helical antenna (which I believe is actually built into the phone), out of a q-tip and a single strand of stranded wire.

For the ultimate in range, you could probably put together a yagi-style directional antenna which would allow you to reach a tower 10-15 miles away in direct line of sight, and all for a half an afternoon of work and $15 in hardware. I've put together a "cantenna" (search the web) for my wireless network and have a fast connection to a neighbor's a 3 miles away. I also built a "pentenna" (own design) which is pretty much a 1/4 wavelength microwave dipole inside a BIC pen housing. Boosted signal strength from attic to basement from 10% to 95%.

I think antenna boosters are worthless. I haven't tested them, but they look like a passive RF repeater with a panel-antenna. Of course they boost the received signal by providing a larger resonance element, but at the same time they would weaken the outgoing RF signal because the transmitter now has to excite a larger chunk of metal. Aside from that, a passive repeater loses about 50% of the transmitted RF power by design. And I haven't even said anything about directionality yet...

Phone manufacturers have some pretty smart RF engineers on staff. You can rest assured that for 99% of your use, the built-in antenna is optimal, and for the remaining 1% a $7 "signal booster" won't help you either.

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Passive antennas work but require experimentation.

Even cellphones with no external antenna connection can be
"connected" by placing the proper antenna near the phone itself.

See attachment for WORKING example.

Of course if you have ZERO bars on your phone inside a building
even if you could double your signal strength it might not be enough
and some time of amplifier may be required.
Experimentation, along with a little coax and time will pay off.

Remember that some cellphones can take up to 10 seconds to
update their signal strength meters so make changes S L O W L Y.

Enjoy,