Signal strength differences

I'm retired and new to android phone use, but the wife gave me a Samsung s3 (necessitated by eliminating our hard line). Other than accustoming myself to using my finger rather than a mouse , I've encountered minimal problems. The phone is on a Sprint shared plan that also includes the wife's phone and our networks aircard. The two issues that concern me are :
(1) At my home location, the phone has a significantly lower signal strength than the aircard .
Phone : 1 to 2 bars on 6 bar scale with an Lte RSRP -120 dbm to -100dbm and
dropping to 3G about 30% of the time. Web connection works only
about 40% of the time and I can't connect to my security IP cams unless
it's wi-fi connected to the LAN and uses the aircard's internet
connection.

Aircard : Full bar 4Glte signal at solid -77 dbm - always excellent web
connection.
Obviously, the devices must be receiving different signals with different strengths and frequencies. Can someone explain ?

(2) : When the the Samsung s3 is not being used, but is powered on and idle
with screen display off, it will periodically power down and back up - no
notifications or other events present. Why ?

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