These are the last of an NOS consignment which appears to have done the rounds.
Mini-Circuits 15542 Splitter ZSC-3-1. It provides for a 50 Ohm, 3-way, 0° split of the source signal with over 35dB isolation between output ports at 200MHz.
Alternatively, of course it will happily SUM 3 input signals; diversity reception anyone?
Connectors are BNC.
These are small signal devices - matched power rating is 1 Watt. MAX load dissipation is 0.375 Watts.
Frequency range is 1 - 200MHz.
Full specification available at: Mini-Circuits' (interactive!) web site where you will also find that this item will set you back all of US$ 51.99, plus shipping.
Priced at £5.00
[UK P&P is included - Overseas: at cost.]