Elecraft KXPA100 Programmers Reference - Manual (Page 20)

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^
SB (ATU Bypass SWR, GET only)
GET format: ^SB;
RESPONSE format: ^SBnnn; Range is ^SB010; to ^SB999; for 1.0 to 99.9 SWR.
^SB is the SWR of the antenna, as measured at the KXPA100 coupler, when the KXAT100 Antenna Tuner
was last in bypass (which occurs in each full search tune).
^SI (ATU Side Relay, GET and SET)
GET format: ^SI;
SET/RESPONSE format: ^SIT; or ^SIA;
Gets or sets the state of SIDE relay K117.
The selected capacitors (see ^CR) are connected to the transmitter side of the inductor (a CL network)
when K117 is not energized (^SIT;)
The selected capacitors are connected to the antenna side of the inductor (an LC network) when K117 is
energized (^SIA;).
The inductance is in series between the transmitter and antenna connector. The capacitance can shunt
either end of the inductor.
Generally, the capacitors shunt the higher impedance side.
It may take a few tens of milliseconds after issuing ^SIx; before the relay is changed.
The SIDE relay is released while the bypass relay is bypassed. The antenna tuner changes the SIDE relay
as needed during tune operations.
This command is meaningful only if the optional KXAT100 Antenna Tuner option is installed.