GSM repeater

Hi!

I'm curious what it takes to build a GSM-repeater (I'm a newbie when it comes to rf-design). I've got a cabin where the reception is poor almost everywhere, except a few places outdoors. My idea is to build a GSM-repeater/booster, place it where there's good reception, and make it possible to use my cellphone inside and around the area where the cabin is. If someone could give me some pointers on what I should start reading up on, and where I should start, I'd be very happy.

In advance, thanks!

Basically, it's horribly complex. And probably illegal.

Might a 'fixed' mobile phone with an antenna to where you get good reception that you put your SIM in, with a DECT phone plugged in work? I'm sure I've seen 'mobile phones' that present an external phone socket.

That's what I feared, yes :(

Not very worried about that, not going to repeat the signal for a very big area.

Nope, need to be able to use several phones at the same time.

I am 99% sure that GSM is TDM, with 4 voice channel uplink and 4 voice channels downlink per frequency. So, you can't just boild a repeater, because the two directions of transmission are on the same frequency. You could put the phone on top of the hill, and run a full duplex analog radio link down to the cabin; but, if you did that, there would be no way to dial out, since it does not use inband signaling. Some people claim a passive repeater, consisting of two high gain antennas back to back works. Polarization should be vertical.

Tam

I read in sci.electronics.design that Zak wrote (in ) about 'GSM repeater', on Sun, 25 Sep 2005:

Must be better than baloney.

-- Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection.

No... it is TDM with 8 or nowadays 16 slots per frame. Uplink and downlink are on different frequencies; this makes it possible to synchronize phones to arrive at the same time at the base station while not interfering with each other's reception.

I's tru a yagi. Might even be a passive repeater (with a small antenna indoors just wired to the yagi) could work if the problem building is in a shadow.

And a yagi or other high gain antenna is a nice project for a rainy winter night...

Check the frequency - is the phone dual band? Where is the base station? What frequency(ies) does that base station use?

Maybe a ham could help in this situation.

Thomas

Is the "direction" of the frequency fixed aswell over time ..?, or is it changed dynamicly during operation?

If not maybe some antenna amplifier + filters could do the job?

I hadn't looked at a spec in years, but the 8 slots refers to the total U+D. So, in a very thin cell you would have 4U and 4D. Where the 16 comes from is if you have 1/2 rate channels, with full rate being about 13 KHz./ch. Somebody mentioned maximum distance. It is 35 km, before the round trip delay gets too long. You can do all kinds of stuff in G3.

Tam

If you are beyond the time/distance limit to the cell site, all the antennae in the world won't help you. Just how far away is the cell site that you occasionally get into?

Ken

I don't know how far away it is, but I get 3 out of 5 "dots" on my SE K700i where the reception is at it's best. (This is where I had plans for setting up the repeater/booster for the area).

antennae

K700i

setting

It's doubtful you'd get that much signal if you were outside the coverage area of a cell so playing with antennas is worth a try. I think someone mentioned getting a car type antenna for remote mounting - this may be possible to put at the end of a cable and some distance up a tree or at least in a convenient good location.

Good luck!

Ken