[Today’s run: 7 miles with Boardtown Runners]
Today’s picture is of a dual port RF isolator for the VHF range (this one says 160-174 Mhz on it’s label).
A dual port RF isolator can be used as an RF separation between a transmitter/receiver and the antenna. As I understand, it is kind of a one-way gate that allows the signal to pass in one direction only. Anything going in the other direction is shunted into another port to which is usually attached a dummy load (dead end).
In this picture the isolator is the larger rectangle. Two dummy loads are attached, both of them have heat sink fin structures. The smaller black box is a harmonic filter which helps attenuate overtones of the passing signal.
A setup like this might be used as part of a repeater duplexer, in combination with some cavity filters. Here is a write-up on circulators, isolators and their uses from the www.repeater-builder.com website.