Hello,
I just got into SDR and bought a preamp from ebay, the cheap ones.
As I see, it has a separate 5V supply. Since my sdr dongle has bias-t support, I'd like to send the power through the coax to power the preamp.
After seeing some other devices online I figured I can just add a choke between the output to the sdr and the 5V input on the board.
It uses the SPF5189Z amplifier.
PDF here:
http://www.rfmd.com/store/downloads/dl/file/id/28188/spf5189z_data_sheet.pdfAnd the application on my board seems to be identical to the one in the datasheet. There's three 0 ohm resistors added, but the rest seems to be the same.
Now, I see two ways of powering the amp via the coax. One would be to remove the output capacitor and the inductor feeding the voltage to the chip, and bridge the capacitor pads. But that is not the recommended application.
The second way would be to add an inductor between the output sma pin and the 5V pad. I can wind an aircore inductor at about 2uH or so. Would that be ok?