Generally speaking, however, the two units connects to each other using the same 5Ghz frequency in Wi-Fi technology. That said, the distance between them varies from between 150 feet to up to 350 feet, depending on the environment. In optimal settings, a Cel-Fi set can offer up to 13,000 square feet of cell coverage with support for 60 connected units at a time. You can actually use multiple sets together to increase the coverage area and number of concurrent users. In my testing, there seemed to be a minimum distance, too, and the Window and the Coverage unit needed to be at least 50 feet away from each other sync up.
In all, it was very easy to set up a Cel-Fi set. Apart from finding out the right distance, the rest is just plug and play.
No support for 4G LTE In my trial, the Cel-Fi indeed helped a great deal with voice signal and I was able to make calls and hold a long conversation in places I couldn't before. The data also worked well. When the Cel-Fi was turned on, my test T-Mobile phone also showed full bars indicating the improvement in signal strength. But that was also because the phone was not tuned for 4G LTE. When I tried a 4G LTE device with the Cel-Fi, it had no affect on the bars as well as the cellular data speed. Nextivity says though the Cel-Fi doesn't support 4G LTE for data, it should helps with voice even when you use a 4G LTE phone with it.
For now the Cel-Fi supports only 3G and 4G HSPA+ standard. Nextivity says that going forward, there will be a newer version of the Cel-Fi that will also works with 4G LTE.
Performance It was a little hard to test the Cel-Fi due to the constraint of my environment and the fact that cell coverage, of both AT&T and T-Mobile, is generally good in the San Francisco Bay Area. But, as mentioned above, I was able to see the improvement, quite significantly for both data and voice. It's interesting that it worked well for voice even when the Windows unit showed only just one or two bars.
I was able to put the Coverage unit some 250 feet away from the Window unit and have them both synced up. (Note that I couldn't move it further due to a lack of wall sockets and maybe the distance could get even longer.) In this case, in theory, you should be able to get signal improvement up to 500 feet away from the Window unit as long as you stand directly across the Coverage unit. In my test, again, I couldn't move further away than some 300 feet, simply because I was already in the basement.
When used in a multiple-story home, the signal could penetrate to the basement quite easily. In all, the Cel-Fi indeed helps enhance the cellular signal where it's used.
Conclusion The Cel-Fi is truly a plug-and-play device that greatly improves cell signal. It's an excellent alternative tosince it doesn't require a broadband Internet connection to work, allowing you to seamlessly continue your conversation when moving in and out of the house.
The device's main shortcoming is its cost, which is more than three times that of a Femtocell, making it only a viable solution for a business, rather than for a home. And the fact that there's no support for CDMA means Verizon and Sprint users are completely discounted, for now.