here is how Craig (the designer) describes it:

The receiver's Noise Figure may be improved when using the SW Preamp,
especially if the receiver's preamp can be disengaged.

The SW Preamp has excellent signal overload immunity. It typically
measures 20 dB better than the average receiver. Third Order Intercept
or ICP3 is a measurement of signal overload characteristics. The SW
Preamp ICP3 measures +34 dBm. A typical table top receiver measures +4
to +10 dBm. The Drake R8A specifies an ICP3 of +10 dBm with the preamp
engaged.

The balanced input allows proper termination to balanced antennas such
as a two wire beverage antenna, or T2FD antennas. Kiwa will soon have a
phase switching control unit available for balanced beverage antennas.
This control unit would connect to the SW Preamp output and the
CT-Center Tap connection providing the ability to switch the receive
pattern of a two wire beverage antenna. (In one position the receive
pattern would be from one end, the other position would switch the
receive pattern to the other end.)

Reception below 1.8 MHz is possible when using a long-wire or beverage
antenna by connecting the receiver input to what is the 50 Ohm Input.
In this configuration the input transformer is acting as an impedance
matching device to the 50 Ohm Input and signals are passively coupled
to the receiver bypassing the BCB Filter and Preamp.

Price: $109.00