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homemade signal booster? Answered

i was trying to figure out how to boast my signal coverage in my area, and a got an idea:

to use a UHF amplifier, to pick up the towers signal and rebroadcast it. of coarse since things like WiFi, Bluetooth, and cellular 2G/3G/4G networks use two way radio, the signal can go back to the reviving end of the UHF amp, and get broadcasting to hit whatever tower. my phone should better recognize the tower, as if i just magically made a tower 2 feet away. however this might also amplify stay noise.

if this idea doesn't work, why not? i think i am going to need at least a 20dB increase in power, but as of now i  need to do more research.
but if i can buy a product that does a similar thing for less than $40, i would.

http://en.wikipedia.org/wiki/Wireless_spectrum (cellphones use UHF spectrum)


I believe that this may be more complex than you anticipate. As I understand it, you want to amplify a weak cell signal. The typical solution is to use a direction antenna (such as a Yagi-Uda or double bi-quad with reflector) tuned to the frequency that your provider uses (many providers use different frequencies) which would be connected to a low loss cable (like an lmr400) to a bi-directional signal amplifier (again, tuned for the correct frequency) and out to an omni-directional antenna. This gets further complicated if you use providers like T-Mobile, who server 4G/LTE on 1700/2100 (transmit on 1710-1755 MHz and receive on 2110-2500 MHz) This would, I believe, require either two different sets of antennas and amplifiers, or one set that covers a very broad bandwidth (1700-2200 MHz).

The solution above assumes that you have a weak to moderate signal outside within reasonable distance of your location that you want to amplify and bring into your location. For instance, if you stand in the yard outside your home, you get 2 bars or -100dbm, but inside you get no bars/no signal/ -125dbm or worse.

If you get good signal outside (full bars, or -50 to -75dbm) you may be able to use a passive setup, which is the same as above, but without the signal amplifier. This will work because the antennas will boost the signal.

In either case, the factors to consider are the strength of the original signal, the signal boost of the outside antenna, the signal loss over distance of the cable to the amplifier (if present), the signal amplification from the amplifier, and the signal loss over distance of the cable to the inside antenna. In the case of signal measured in decibels, the measures are logarithmic, meaning that a gain of 3 dbm is a doubling of signal strength.

Another issue is that you CANNOT interfere with anyone else's listening or communicating devices. If you are in the U.S. the FCC has some very specific regulations (laws) about what you can and cannot do. Further, you are required by law to get the permission of your provider (Cell Phone Company) and register your device with them (again, in the U.S., other countries YMMV)

So, a step-by-step suggested solution:

1. Find out what frequencies your cell phone provider uses

2. Research Yagi-uda, double bi-quad and omnidirectional antennas online, as well as looking at vendors with pre-made solutions and determine if you will purchase or build your solution. (If you need a signal amplifier, I suggest purchasing, as the electronics skills involved in building a bi-directional cellular signal amplifier are beyond the casual tinkerer).

3. Map the strength of signal around your area. You must have SOME signal within a reasonable distance of your location, or these solutions will not work.

a. Search the internet for the command or method to put your phone in "field test" mode - This should give you a numerical readout of signal strength, as opposed to "bars"

b. Walk around outside your location and note where you get the strongest signal. This is where you will want to put your outside antenna.

4. Mount your external antenna at sufficient height or location to get past any obvious encumbrances (trees, buildings, etc.)

5. Connect the amplifier (if used) and internal antenna

6. Using your phone in Field Test mode again, point your external antenna at the nearest cell tower for your provider.

It's not easy, it's not simple, and it's not fast, but with leg work, you should be able to achieve a nice boost in signal strength. That's the theory, anyway.

And rereading my original question I can't believe how unclear I was lol! I have since learned a lot, and it seems that these repeaters appear to operate in the digital domain. (demodulation, ADC conversion, extracting data packets and ECC and stuff, DAC conversion, and remodulation on a different frequency band or channel or something.)

What you describe at the beginning is precisely what I wanted to do, just for 4G signals. (I beleive that is 1900MHz with sprint)

Wow, great long reply. This question is pretty old now, I forgot about it and gave up on the idea since getting new phones which do receive 4G coverage pretty well inside the house. I might try the passive solution for the basement though! I never would have thought that a passive solution could work. Impedance matching the antannas might be challenging though.

Where will you get the UHF amplifier from?

How will you tap into your phones circuit to extract the Rf signal to drive the amplifier.

The cheapest option is to add an external antenna.

\i plan on buying one, ir if i can, build one. i am sure the gain is going to have to be very high, it might be cheaper to buy a few cheap ones and hook the output of one to the input of the next one to get exponential gain, maybe 3? the last one is going to be a higher wattage to emit the signal. this i think should work.

the phones emit rf signal into the air, so i make an antenna to pick it up and re amplify. the amplified signal goes to a emitting antenna, both i might cheap out on and just use a 5 inch long coiled up wire. (helical design)

i tried to place a wire to the 1/2 inch long antenna, only to find out whatever i did i decreased my signal strength. (from 98dbm to 110dbm, from 1-2-ish bat to nothing..) i was able to get better WiFi signal however, with a 1.5 inch steel wire. :)

besides, it would be weird to carry a phone with a antenna sticking out the top of it,(especially on a galaxy s3) that is SO 90's

I have a feeling this isn't going to work - BUT your making the best effort by buying the complicated parts e.g. the UHF amp.

Let us know how you get on.

i also have my doubts, i have no way of knowing if i built a working amplifier, and if i did, how much gain would i need, how do certain dbm gain translate to the actual gain? (3 times, 10 times, 100 times 200 times increase in gain?)

then my last problem would be, if i did get all of that to work, and everything is the right rating to work properly, then what if all i end up amplifying is just as much noise as the signal? it is probably my biggest concern.