The testbed's programmable RF attenuator matrix — a JFW 50PMA-012 — sits between the radios of the SB4 sandbox, letting you set the path loss between nodes in software. Instead of hoping the over-the-air channel cooperates, you dial in a repeatable topology: strong link, weak link, hidden terminal, gradual fade — the same every run.
| Instrument | JFW 50PMA-012 programmable attenuator matrix |
| Where it acts | RF paths between SB4 node radios (9 matrix ports, mapped to node antenna feeds via RF switches) |
| Control | Portal → Status → RF Matrix panel, or the rfmatrix testbed service during an SB4 reservation |
| Granularity | Per-path attenuation, settable in dB steps across the matrix |
Reserve sb4.cosmos-lab.org, then either use the portal's RF Matrix panel (live view of every path's attenuation, click to set) or script it against the rfmatrix service via the AM proxy:
curl "http://am-rt1.cosmos-lab.org:5054/rfmatrix/status"
The service's port map translates "node1-3 USRP TX/RX" style names to matrix ports, so scripts don't need to know the cabling.
If the portal shows an amber "RF Matrix Unavailable" banner, the matrix hardware is offline — report it to problems@cosmos-lab.org rather than debugging your experiment.
See the SB4 page for node hardware and the exact matrix wiring.