Here's some more feedback after a day of playing with my 4G LTE Signal Booster.
I found a temporary outdoor location for the window unit that seems to get a pretty steady 1 bar LTE signal. The repeater unit is inside our cabin and is now showing 4-5 on the display.
I have an iPhone 5S LTE connection thru the signal booster with about 3 bars when I am sitting next to the repeater. When I run speed test I get 92ms ping; 11.83 MB down; 0.47 MB up. I can also us the personal hotspot with my laptop and everything runs pretty well.
However, I can't make ANY voice calls. Every call I try to make fails, and the iPhone then temporarily shows no service.
When I put the iPhone in my reliable window (getting 1 bar LTE without the booster), I notice similar behavior. When I try to make a voice call, after a short delay, the iPhone drops LTE and switches to either Edge or just T-Mobile and then the call goes thru.
Anyone have any idea what is going on here? Without voice call capability, the signal booster is essentially useless.
I'm not an iPhone guru but when I look both on this site and GSMarena.com I do not see VoLTE mentioned in the specs for the iPhone 5s. If a phone does not have VoLTE it will have to drop back to 3G or 2G to make voice calls. If the booster is not compatible with 3G or 2G, this might be an explanation. Does that make any sense?
I ended up talking to T-Mobile tech support and that exactly is the problem. The iPhone 5S does not support Voice over LTE (it is supported by the iPhone 6), so it drops back to 4G, 3G, Edge, or GPS to make the call. The T-Mobile 4G LTE Signal Booster does not boost 2G signals, and the Milltown WI area towers only support 2G and LTE.
Looks like a new phone is in my future (hopefully the new iPhones will support the T-Mobile 700 MHz LTE spectrum; that might also help my coverage issues).
I still have to figure out where to put the window and coverage units so that I get more separation with less interference and a stronger booster signal.
Just a couple of thoughts.
700 MHz is going to be very important in Wisc. If you're dedicated to iPhones, you might get an iPhone 6 under JUMP Mk 3. ("On Demand") and upgrade to the 6x when it comes out. ITMT, you could try using a VoIP client (e.g. Viber, Skype, etc). Get an inbound VoIP number and forward incoming calls to that number when you're at your cabin. Make outbound calls via VoIP. I don't know how well this would work but it might get around the VoLTE issue until you get a phone with VoLTE.
T-Mobile overnighted me a Signal Booster for use at my work. I'm in a large building that only gets signal near the windows. I already had a home router from T-Mobile and they didn't charge me shipping or a fee for this second device. T-Mobile is great! Even if another provider had more affordable cell service, I'd stick with T-mobile out of pure loyalty at this point.