These are normally built on request and will have a lead-time of about 2-3 weeks. Sometimes they might be in stock which can be seen in the stock status.
The stackbox is a device which is used to split power between up to three antennas on 1.8 – 30 MHz. It can be used to switch antennas in a stack or for beaming multiple directions. A stacking system that is made this way is simply an approximation of a two way and three way stack. The UN-UN transformer has got a ratio of 2.25:1 and that way you will get about 56 ohm with two 50 ohm antennas connected and 37.6 ohm with three antennas connected. It means that with with two antennas you will have about 1.1:1 in SWR and with three antennas about 1.35:1 in SWR if the antennas are a perfect 50 ohm match. With a single antenna the VSWR is < 1.1:1. It can also be used as a regular antenna switch for three antennas and of course it is switchable between these different modes.
The device uses positive switching, which means all the relays use common ground. So to enable an antenna you would add a voltage of +12V on the control line. 5 leads are needed to switch it. No control box is included.