I just purchased a Skystars f411 hd flight controller and Im wondering if I can use it with a spektrum fpv racing serial receiver with it? If so, how do I do it?

Assuming you will be using something like the Spektrum SPM4650 receiver then you just need to wire the "S" connection from the receiver to the TX1 pad on the Skystars F411 Mini HD FC (along with the 5V and GND connections), then configure Betaflight to use UART1 for "Serial RX" and the Serial Receiver Protocol to be "SRXL2", not forgetting to also switch on the "TELEMETERY" option.

If you are flashing Betaflight 4.4.x then don't forget to select "SRXL2" for the Radio Protocol in the Build Configuration section before flashing the firmware.

Just looked up the info. My receiver is the spm4648.

A Spektrum SPM4648 receiver needs to be connected to an RX pad (not a TX pad), so on the Skystars F411 Mini HD FC you will need to connect the signal output of the receiver to the RX1 pad. The SPM4648 also requires 3.3V to power it (not 5V), so be sure to connect it to the 3.3V pad on the FC.

For the Betaflight settings, you will need to set UART1 to be for "Serial RX" and select "SPEKTRUM2048" as the Serial Receiver Provider. The SPM4648 doesn't have telemetry so there is no need to switch on the TELEMETRY option.

If you're flashing Betaflight 4.4.x you need to select "SPEKTRUM" for the Radio Protocol in the Build Configuration section before flashing.

Thank you. That worked.

No problem. Happy flying