# A bias-tee powered LNA

> A wideband SPF5189Z low noise amplifier for an SDR, from schematic to a routed four layer layout, with FDTD, a cascade with vendor data, DC drop and thermal sims.

- Board: 4 layers, JLC04161H-7628, ENIG
- Band: 50 MHz to 4 GHz
- Cascade at 900 MHz: gain 17.7 dB, NF 1.0 dB
- Sims: FDTD, cascade, DC drop, thermal

The amplifier sits at the antenna end of an RTL-SDR style receiver: SMA in, SMA out, a Qorvo SPF5189Z in the middle, powered either over the output coax by the receiver’s bias tee or from a 5 V header. Two Schottky diodes let either source power it without one feeding the other.

The RF lines are a field solved grounded coplanar class at 50 ohm on the top layer over the In1.Cu plane, with the pour beside it stitched to the plane every 2 mm. Its `DESIGN.md` records why each part was chosen, which chokes stay inductive up to 4 GHz, and the layout rules the circuit depends on.

The simulations show the usual split for RF work: an FDTD run of the passive board with a port where each active part sits, then a cascade that drops in the vendor `.s2p` files and the datasheet noise figure and OIP3. Change the board and rerun the FDTD; change a part and rerun only the cascade.

Files: https://github.com/v0l/agentee/tree/master/examples/lna