It is a buffer or isolator between radio and linear amplifier. Basicly,
this box as well as the one I sent a link to yesterday is keyed by the
small relay in the radio and the box then keys the amp. Most radios have
a very small voltage and current rating which isn't enough for some
amplifiers.
HTH.
73
Butch
WA0VJR
Node 3148
Wallace, ks.