FlightAware Discussions

Using Bias-t to power the RTL Triple filtered LNA

I am proposing to use the RTL triple-filtered LNA with an Airspy Mini, and to power the LNA using a Bias-t. I have never used a separate Bias-t before and have almost no expertise of electronics. I was planning on purchasing the following bias-t:

Is that suitable for what I am intending?

Also a very naive question but how do I power the bias-t?

Many thanks

I have a very similar bias-t injector. Works fine as long as you feed with the proper voltage (5V).
I feed my RTL-SDR LNA with 5V from a separate power supply, but you can use a wall-wart for cellphones and a USB-cable where you cut the end of the cord and brings out the black and red cables. Black is usually ground (GND on the left side of the blue terminal on top) and the red one is V+ (VCC+ on the right side).

Make sure you connect the LNA (marked OUT +5V) to the proper side of the power injector (DC+RF).
The SDR-stick connects to the bias-t injector (marked RF) and the antenna connects to the LNA (marked IN).

Many thanks for such a detailed and helpful reply. Presumably if I was to use a USB cable it could be powered from a spare USB socket on the RPi?

I am using an Airspy in combination with the Uputronics filtered LNA.
I do not use the power from the Airspy’s Bias-T but have it connected via USB-Cable to one of the USB ports of the Raspberry.

Works without issues.
But make sure that the power supply of the Raspberry is sufficient. I am using the original Raspberry power supply, delivering the right power.

I tried it also with a seperate power supply (a small smartphone charger) going to the LNA, but it did not deliver a difference

Many thanks. I’m currently using the Uputronics LNA with the Airspy Mini powered using the Airspy’s Bias-T. I wanted to see if the RTL LNA was any better. I’m assuming the USB port on the Raspberry will provide the 4.5-5V needed to power the RTL LNA as that is more or less the same as powering the Uputronics LNA via a USB cable from the Pi? It’s a RPi 4B and I’m using the Raspberry power supply unit.

Thanks

Yeah that works, just chop up an old USB cable and connect it to the bias-t.
Be sure to mind the polarity :slight_smile: