Cell phone repeaters only bring signal in from outdoors?

Cell phone repeaters, the little amplifiers you can put in your house with an outdoor antenna to provide cell phone operation indoors where it didn’t work before, all seem to collect a signal outdoors, amplify it, and rebroadcast it indoors. At least, this is the pretty clear description I have seen on each of several different vendor’s websites. None of them say anything about collecting a signal indoors and sending it out to the tower. Usually the diagrams are drawn in an exclusively one-way fashion, outdoors to indoors.

But of course cell phones are two way radio systems, so the phone also transmits and the tower also receives. In fact, because the phones are small and use batteries, this uplink seems to me like it would be much more challenging to make work well than the downlink that repeaters say they amplify.

So what’s wrong here? Are they describing their products wrong, or does some other element of the system behave differently than I thought?


As far as I know, they all work two-way. The phone talks to the repeater, and the repeater talks to the cell tower. I can tell when my phone is connected to the repeater by the status lights.
I have one, and I’m not very impressed with it. It’s a marginal improvement over nothing, but that’s about it.

A cell-phone repeater it is much more complex then that. I think the vendors are mistaken as to how these systems work or what they are selling, but, if you provide links I can look at them and provide some technical feedback.

The TX and RX each operate on different frequencies, usually. Also, cell phone systems are a little more complex than a CB radio. The tower and phone(s) constantly talk to each other. One of the things that they talk about is their respective signal strengths. If your phone says it has a low receive signal strength the tower can increase the TX power for just that phone (within limits). Now, for your phone, it’s a different story as it has a very real limit on how much power it can put out. The new phones now have very little capability as there are a lot of towers than say, 10 years ago, so its not needed. This is why in a city your battery will last longer than out in the country as the phone can operate in a low-power TX state.

Now, theoretically, you could make a bidirectional, RF, amplifier of low-power to boost the cell signal. However, going by what I know, this has a great potential for interference and could make things worse for everyone. But, you could make an RF amp that boosted the band of the frequencies that you would be transmitting on and the tower takes care of the signal strength to you. This may be what the companies you refer to are advertising.

As far as my experience is concerned:

I actually installed a commercial cellphone repeater system for a building I used to work in. We had poor reception for our Gov’t phones when it came to email so I was tasked with solving the problem. Through research I found out that a cell-phone repeater is actually a micro-cell-site. It talks to the tower, tells the tower which phones it has so the tower ignores them (to prevent interference), and talks to the phones to tell them which site they are on so they don’t try and hop between the two dropping calls. It is actually expensive and complex as you have to have the antennas within your building professional placed by an RF engineer. This involves providing building details such as where the cement walls are, building material, etc.

electronbee provided a good explanation of how the repeaters work, but I’m going to suggest a “microcell” if you have high speed internet available. I received one for free from ATT and it works fine. I live in the county and before the microcell I often had no service. With the microcell I have fine service both ways. I pay no extra fees and am satisfied.

GaryM, how does the internet side of the microcell get back to the telephone network? Do you need a VIOP service provider or some other service? Do you still have the same phone number if your phone is working through a microcell? I have cable internet and have ethernet through the house plus wireless. Some little box that ties to the ethernet would be way easy.

Searching Amazon for “microcell” just gets me all the “cell phone signal boosters” that I have been asking about already. The Wikipedia article on “microcell” seems to describe a device that the phone company would use from within their system. None of these hint at internet connectivity, at least not that I noticed.


BTW I turned up a reference somewhere that says that the “cell phone signal boosters” that I am looking at operate as their own tiny little cell phone towers, and relay things to the phone company’s tower. Thinking a little further, it seems like it would HAVE to work this way. The “signal booster” talks to the phone and tells the phone “I’m the one you are talking to, ignore the weak signal from the tower”. It also tells the tower a similar thing. Otherwise, there would be a huge interference between the two sides of the “signal booster”. It seems obvious now that these devices must handle two separate conversations on two separate channels, from the point of view of radio technology.

What AT&T is calling a “microcell” is more commonly called a femtocell.

Sprint gave me one of theirs for free with no monthly service charge, either. It works well. Yes, you have the same phone number when your cell phone goes through the device. Your telephone provider is providing the internet end of the service as well. My Sprint unit has the ability to plug a landline phone into it, and use it like a VOIP service as well, which is a second number. But as far as your cell phone is concerned, it’s just a cell tower it’s practically on top of, and you have five or six bars. The one I have has a little confirmation beep when you receive or make a call through it, to let you know the thing is routing the call over the internet. Femtocells supposedly cover about a 5000 square foot area, which is ample for most houses.

One rub - they may have a GPS antenna on them, and have to get a GPS fix to work. In addition to technical reasons, this keeps you from getting around international charges by taking the thing out of the country. The GPS antenna will typically have a long cord on it, and you may have to place it some distance from the femtocell to get a decent GPS signal. I have a metal roof, and actually had to string mine outdoors.

As the wiki article notes on the term “femotocell” vs. “microcell”:

I received the same thing from AT&T earlier this year. Despite being in suburban Chicago, our area has terrible cell phone service, and the “microcell” gives us an excellent signal in the house.

Note that it only works for our phones, and phones for our friends who (a) have AT&T for their wireless service, and (b) we’ve entered their numbers into our account for access to the microcell.

Seems OP is talking about a BDA (Bi Directional Amplifier). These have just as much likelihood of causing harmful interference to the carrier’s network as they do improving the user’s signal quality.

If so, it’s worth noting that deploying one of these is contrary to FCC rules unless you have permission of the carrier. While you won’t go to jail for it, fines can range up to $5000 per day.

I think I have been talking about two different products, and confusing them, and some of my references confuse them. But it seems pretty clear most of the things I saw were BDAs, as IAmNotSpartacus concluded. They are mostly incorrectly described as only amplifying the signal from outdoors inward, whereas they must amplify both. Some of them described this way have further details in their descriptions that do say they amplify outward too, contradicting their earlier descriptions. I did find some real cell repeaters, too, and it was hard to figure out which ones were which.

yabob and kenobi 65, what you describe is interesting. Where I found them, they were called “network extenders”, by which they mean the telephone network, and not the home ethernet network to which one attaches them. Oddly, they include a GPS unit, and it has to have a good enough view of the sky for the thing to operate (for which purpose they include an external GPS antenna in case the embedded one doesn’t work). This is so it can tell emergency services your location. I guess typing an address into some config file isn’t good enough. I see Amazon sells them “new” for around $100, and many of the people who use them rate them highly - but about as many rate them terribly because they aren’t “new”, they’re used or refurbished, and often still have the previous owner’s configuration and account attached to them. Apparently they sometimes cannot be made to work because the previous owner did not release them. A bizarre twist for Amazon! Verizon sells the same model device for $250. In their FAQ I see that it does not matter whether Verizon is the ISP. This is actually pretty tempting looking - can’t see any reason it wouldn’t work. Of course there are LOTS of things that don’t work for reasons I don’t see…

Yes, the one which I got from AT&T has a GPS in it; the set-up instructions included being certain to have it near a window during its initial boot-up.

Several have already provided answers, but since I’m here…

It uses the internet, DSL in my case to place and receive calls. It’s plugged into my router via Ethernet cable. It needs to be near a window for GPS, I don’t recall seeing an external GPS antenna connection.

On my iPhone I get a header that says “AT&T M-Cell” when it’s connected. Some friends visited a few weeks back. I logged on to my account and added their phones to the system. They were able to use the unit within 10 minutes.

I’m glad mine came with an external GPS antenna on a 30 foot cord. Their intent was that you could place the antenna by a window while still locating the unit somewhere inside the house for better coverage. It wasn’t supposed to be run outside (“not weatherproof”). When I couldn’t reliably get a gps fix with the antenna by the window, I ran it outside anyway, and put a plastic bag over it.

BTW, I’m also disobeying installation instructions with this thing in the same way that I did with a VOIP box I used to have. It has LAN and WAN sockets on it, and the instructions say that if you have a router, you are supposed place it ahead of the router and let it pass your internet connection through to the router. My old VOIP box had the same instructions. I had no end of trouble trying to get it to work that way. Simply plugging it into one of the LAN ports of the router as you would expect worked fine. I didn’t even try the femtocell their way. It’s a peer on the router network along with the PC, and has nothing plugged into its two LAN ports.


I suspect their instructions have to do with wanting to tell people that their router has to support VPN pass though, and it has to be enabled.