Which port is which¶

Read the board, not the box. On some PlutoSky R1 units the case's SMA labels are in the wrong order: what is printed on the case does not match the ports on the board behind it. With the lid off, each SMA has its name on the silkscreen beside it: TX1A, RX1A, TX2A or RX2A.

The cased board from its antenna end: four SMA connectors with yellow caps in a row. Labels say they are TX1A, RX1A, TX2A and RX2A, that which is which is read from the board's silkscreen with the lid off, and that the case's own labels are in the wrong order on some units.

The case's antenna end. The photo cannot tell you the order: the silkscreen can.

Connector	What it is
4 × SMA	`TX1A`, `RX1A`, `TX2A`, `RX2A`: the AD9361's `A` ports (its `RX1B`/`RX2B` pairs are not wired)
`RF1` (U.FL)	`EXT_CLK`: connected to nothing as shipped (external reference)
`RF2`, `RF3` (U.FL)	`TX_LO` and `RX_LO`: the AD9361's local oscillators, brought out
2 × USB-C, USB and DEBUG	use both, one on a mains charger: on laptop bus power alone the board browns out under sustained use
`JP5`	the 2×10 expansion header (wire to JP5)
`BOOT1`	the boot switch: SD `0 0`, QSPI `1 0`, JTAG `1 1`
`RED1`, `BLUE1`	the two LEDs, each through 240 Ω

The board photographed from above, with 22 labels: the four SMA ports, EXT_CLK, TX_LO and RX_LO, the AD9361, the Zynq XC7Z020, two MT41K256M16 DDR3L chips, the RTL8211F Ethernet PHY, the HR911130A RJ45 jack, the JP5 header, the BOOT DIP switch, the reset button, the microSD card and both USB-C sockets.

Check a receive port without opening the case¶

Receive, with nothing transmitting. Put an antenna on one port and watch the FM band in SDR++, switching RX Port between RX1 and RX2.

You should see: stations appear only when the antenna is on that receiver. A transmit port shows nothing on either.

Mixing them up matters most when you loop a transmitter into a receiver

The attenuator has to sit between a real TX and a real RX (before you transmit).

Reference: what is on the board.