PlutoSDR for 433MHz/70cm LNA Testing on GNURadio – Telecommunications, Navigation & Electronics

Introduction

I want to do some experiments in the amateur radio 433MHz/70cm band. So I was looking for an LNA/BPF as I used in previous experiments. I found two units on line, one in a metal case and one on an open PCB. The PCB unit arrived first, so I tested it using white noise. I didn’t see any bandpass, so I assumed it was a broadband amplifier and tested it with the PlutoSDR as a signal generator.

Measurement Setup

Fig.1 433MHz LNA & +5VDC Lithium CellPhone Charger Battery

Fig.3 GNURC Schematic for PlutoSDR Generator

Freq MHz	GNURC Gain +LNA	GNURC Gain No LNA	LNA Gain dB
100	44	71	27
200	43	67	24
300	42	66	24
400	43	66	23
500	44	66	22
600	45	66	21
700	46	66	20
800	47	65	18

Fig.4 PlutoSDR Generator Relative Gains & LNA Gain

Figure 1 shows the 433MHz LNA with the LithiumB+ battery pack. I was not sure if the LNA could use a bias-Tee feed, so I used the VCC/GND power connections and soldered them to a USB cable. Figure 2 shows the equipment layout. Figure 3 shows the GNURadio schematic for using the PlutoSDR as a signal generator. Figure 4 shows a table of relative gains used to record a -40dBm signal level on the spectrum analyzer (actually -20dBm since using in line 20dB pad). The difference shows the LNA has a gain of 23dB at 400MHz and falls off slowly on either side which meets the published spec.