The FRT-7700 is an ultra-compact passive antenna tuner for the FRG-7700 receiver. Designed for operation from 150 kHz to 30 MHz, the FRT-7700 will provide the proper impedance for the receiver, to reject unwanted signals. A built-in attenuator, 60 dB maximum, prevents intermodulation and cross-modulation from occurring when strong signals are being carried to the receiver. Also, a two-section lowpass filter aids in the rejection of interference from strong signals above 2 MHz, when listening to bands in the 150 kHz to 500 kHz range.
On the rear panel there are two inputs, one for wire antennas and one for coaxial connections, and cables for connecting to the receiver.
The physical dimensions (WHD) are 165 x 42 x 205 mm / 6.5 x 1.65 x 8.1 inch, including knobs/connectors and feets, and it weights 0,833 kg / 1,84 lbs.
Now this antenna tuner has been sold (february 2018) to a radioamateur living close to the Baltic Sea, some 45 km south of Stockholm.
References:
http://www.radiomanual.info/schemi/YAESU_ACC/Yaesu_FRT-7700_user.pdf
https://www.universal-radio.com/catalog/commrxvr/frt7700.html
https://www.radiomuseum.org/r/yaesu_antennen_anpassgeraet_frt.html