The Teradek Cube-105 HD-SDI Encoder is the same as Cube-155 except that the 155 additionally features Wi-Fi and an internal battery. If you don't require these, then you can take advantage of the 105's more affordable price.
The 105 connects to a camera by SDI, encodes video and embedded audio and streams these in H.264, in up to 1080p/30, to an optional decoder or to a designated URL, streaming by Ethernet or optionally by a 3G/4G USB modem, which connects into the 105's USB port. You can at the same time also store proxy files to a MicroSD card or stream them to a computer over a network. (You would need to first enable a feature called "Proxy Recording" for free from a Teradek forum.)
Cube can be used camera-top, attaching right into a camera's hot-shoe, or you can mount it onto a rig by an included 1/4" mounting screw. For power, you can use the included AC adapter or you can connect a compatible 2-pin Lemo battery, namely, Teradek's Canon BP-945, Panasonic D54 and Panasonic VW-VGB6. These batteries are sold separately.