Uniden UH7700NB Owner's Manual page 14

Operation
Standard Operation without the aid of a Repeater station.
Operation with the aid of a Repeater Repeater Station (Duplex).
The signal coming from your radio is received by the Repeater Station
and the re-transmitted at the same time on another channel. This
operation is called "Duplexing".
For example,
&+ RQ 'XSOH[ 0RGH ZLOO 5HFHLYH RQ &+ EXW 7UDQVPLW RQ &+
&+ RQ 'XSOH[ 0RGH ZLOO 5HFHLYH RQ &+ EXW 7UDQVPLW RQ &+
etc...
If you transmit on CH01 Duplex mode, you are actually transmitting
on CH31 the repeater station down-converts your signal and
retransmits on CH01.

UNIDEN UH7700NB UHF CB Transceiver