Improving Cell Phone Reception In Buildings?

Amphigory asks: "Not too long ago, I got a digital cell phone. Unfortunately, this phone simply doesn't work in my office even though it works in other parts of the building and even outside the building. For a variety of reasons, I would really like it to. What I'd like to be able to do is put some kind of antenna or maybe a retransmitter from my office to the roof of the building that would allow the signal to get through. Has anybody out there ever done anything like this?" I've heard of systems like this for large convention centers, but I'm not aware of the details. Can anyone shed some light on this subject?

Re:"Leaky" RF Conduits

[Anonymous Coward]

Maybe you can find out how it's done here in NYC. At least two of the car tunnels that carry traffic under local rivers (the Lincoln and Queens Midtown Tunnels, I believe) have some sort of cell phone support system...I've taken car rides through them, talking on my cell phone the whole time.

pick up a personal antenna

[Xel]

We are having one of those building-wide antenna systems installed here, but they are MUCHO DINERO. And I doubt your company would spring for it if, as you say, the reception is pretty godo everywhere else in the building.

you can pick up a little antenna ata cell phone store or I'm sure Radio Shack, I've seen them for under $50. They're meant for cars but they really would work anywhere: The one I've used is a small car-phone like antenna, about 8" long, magnetic base, and a wire about 10' long you plug into the back of the phone. You can leave the antenna in the office and plug into it when youre there. It works very, very well in the car, even in long tunnels where I couldn't anything previously.

Re:pick up a personal antenna

[Freshly Exhumed]

The predicament of cell phone coverage loss is pretty common in the IT world, with so many server/storage farms being in shielded rooms. A business could fork over between $3-5K (US) for a local repeater, but that amount would only scratch the surface. Then you have to factor in construction costs, arrangements with the building owner, local ordinances, licenses, etc. etc. until you start to realize that perhaps a small bubble of dead space in the building is actually too expensive to fix. As far as external antennae for handhelds, the type of cell phone (gsm, cdma, wcdma, tdma) and its frequency range often make them useless. Don't be fooled. Last point: look for external antennae to disappear under product liability pressure once the FCC reviews their SAR values. Every external antenna link causes EM leakage, and the feds are not happy about it.

New Windows

[Anonymous Coward]

I've only had problems in buildings with metal-coated windows. Many of the reflective and darkening window coatings have metal which blocks high-frequency signals very well. Often the signal outside the building is very strong, but is gone five feet from a window.

If you have access to the outside of a window, you might try two automotive stick-on cellphone antennas. The antenna on the rear window of a car is transformer-coupled to the cable inside the car, so you might try two of those back-to-back. If you have cooperative building maintenance personnel, in an inconspicuous corner you could try scraping off a little of the coating where you fasten the antennas, to allow better leakage between the antennas. The building staff might be happy to have a way to get phones to work inside the building. I don't know how many antennas might be needed for an area -- I don't have access to such a building.

"Leaky" RF Conduits

[Chuck Milam]

I seem to recall someone on the Tower-Talk (Ham Radio) list mention something about using passive RF directors run from inside to the outside of buildings, underground tunnels, etc. It was basically coax with holes in the shield used to provide a passive RF path to the outside.

Passive or active

[Matt_Bennett]

The company I used to work for, Andrew Corporation [andrew.com], produced an active transponder that was aimed at improving cellular telephone reception in buildings- it was a panel you placed in a window and had flat antennas on each side. We had an experimental version in our office (our group didn't make these things). You can't just place two antennas with an amplifier between them because amplifiers only go one way, and if you have a return path really close, it is highly likely that they will oscillate.

I have seen passive re-radiators- essentially just a pair of antennas with a cable in between- which might help, but you need to get some pretty high quality cable between the antennas, because the cable losses at the PCS frequencies (up near 2 GHz are pretty high). (I'm guessing this is a PCS or some other non-traditional-cellular (800-900 MHz) cellular phone, since building construction is much less friendly to letting the PCS frequencies through).

For a passive re-radiator to work well, you need to place an antenna outside (not behinid a window- many windows have metallic coatings that will kill RF), preferably in full view of your local cellular phone tower. Run the absolutely shortest cable you can to your inside antenna. Both antennas must be tuned to the frequency of interest. Unfortunately, since celluar phones are frequency agile or spread spectrum, you want antennas that have a somewhat wide band around the frequency band- don't forget that transmit and recieve from the tower may be on separate frequency bands.

-OR- work hard and get a window office. This is probably the most effective solution to your problem.

Indoor transceivers

[cybermage]

I'm not sure how it's done, but I get excellent reception throughout our local mall which is a huge complex of concrete and steel some of which is partially underground. I've been told they have antennas inside the mall, so a solution to your problem should exist.

--

This is what I do.

[Icepick_]

I'm a Radio Frequency Engineer with a major US PCS company. I design new cell sites, the great majority of which are now aimed at improving in-building coverage.

If you're asking what you can do by yourself, the short answer is not much. If you're realitivly close to an area of good reception, you could string an external antenna along, but I can't see that being terribly practical. Also, call up your provider, and tell them that you have no inbuilding coverage at your location. I recieve these reports, and use them to assist in locating new sites. Better yet, do it a couple of times. ;)

If your company owns the building you work in, AND it has a fair amount of phones from whatever provider you use, then talk to your building managment, and give your provider a call. My company has build several microcells upon the request of companies that have bought phones from us. If you can get that accomplished, you'll almost certianly get excellent coverage.