I have a Sprint Tri-Band Galaxy S4. For the past two weeks, I have had no signal in my house.
I talked Sprint into sending me a Airave 2.5+ at no cost. After I set it up, still no bars.
I tried my wife's flip phone and it got 5 bars.
When troubleshooting my Galaxy S4, I first checked "Network Mode" in Settings, it was on "Automatic".
I switched to "CMDA" and got 5 bars, but no LTE Data, only 3G.
When I tried "LTE/CMDA" I got LTE back (Not from the Airave), but no voice.
Which brings us to my question -- Why no CMDA voice in "Automatic" ??
Then just to test, I turned the Airave off, I now had 3 bars in my house from the Sprint tower.
Switching to "Automatic" left me with 0 bars again.
I would think with no signal in "Automatic" mode, it would then seek other bands and find the signal.
I can only guess that "Automatic" seeks the 1900 Mhz band, and Airave is on 800 Mhz.
I can't be absolutely sure because Sprint won't tell me.
If I'm right, why won't my Tri-Band Galaxy S4 find the signal on 800 Mhz??
The tri-band Galaxy S4 is tri band because it operates on three different kinds of signals: CDMA, LTE, and GSM. The latter is only used if it is unlocked for a GSM carrier (T-Mobile, AT&T, etc) or if it is being used internationally in a GSM tower. CDMA is what the voice and 3G/2G(1XRTT) operates off of, LTE is your 4G data services. Those are the two primary antennas used. If you have it set to CDMA only, it will only use voice and 3G services. If you have it set for CDMA/LTE it will use voice, 3G, and 4G (if available), but will not look for GSM towers. Automatic will look to connect to any of those, but will not connect to GSM unless unlocked to do so.
Now, as far as why it isn't working on your airave, if could be a couple things. The most likely is that it isn't compatible with your airave. It has nothing to do with the frequency the airave is using. There are several new phones that the airaves aren't yet compatible with. Assuming that's not the case, you could have a defective phone.
Another fun thing in the mix is the fact that the tri-band S4 is Sprint Spark capable, and for some reason Spark has been causing a ton of issues on phones (i.e. not calling, not texting, no data, freezing the phone up, etc), even in areas that don't have Spark up and running yet. So it's also very possible that these issues lie in the fact that the phone is Spark capable, which may persist even if you get the phone replaced.
There is a good possibility that you may be having Spark issues because right now the work around for phones experiencing issues with Spark phones is to put the network on CDMA only, which you said has given you some relief from your problems. The downside of that is that your 4G won't work with it on CDMA only.
Of course this isn't very good news, but hopefully that sheds some light on your situation.