NanoVNA for 433MHz/70cm LNA Testing

Introduction

In the previous post I tested a 433MHz LNA with a PlutoSDR as a signal generator and determined it had a wideband response over 100MHz – 800MHz with a gain of approx. 23dB. In this post I will do the same measurement but this time with a NanoVNA. I am always looking for an excuse to use this amazing little instrument!

Measurement Setup

Fig.1 Block Diagram of Equipment Setup
Fig.2 Picture of Equipment Setup

Figure 1 shows the Block Diagram of the Equipment Setup. Figure 2 shows the NanoVNA connected to the 433MHz LNA with the 10dB attenuator connected to the RFin and the 20dB attenuator connected to the RFout. The NanoVNA will measure the S21 characteristic or forward voltage gain of a network. First we measure a pad of 30dB (10dB + 20dB) which will have a flat response. Then we consider the amplifier to be a filter with response of -10dB + GainAmp -20dB = -10 + 23 -20 or approx -7dB. The pads are chosen so that we don’t overdrive the amp (max +20dBm) and don’t overdrive CH1.

Measurement Results

Fig.3 S21 LogMag with 30dB Attenuator
Fig.4 S21 LogMag with 433MHz LNA

Figure 3 shows the 30dB attenuation between CH0 and CH1. Figure 4 shows the attenuation with the amplifier inserted. At 437MHz the attenuation is -7dB which corresponds to an amplifier gain of 23dB.

Fig.5 YouTube Video “NanoVNA for 433MHz/70cm LNA Testing”

References

#1. – “PlutoSDR for 433MHz/70cm LNA Testing on GNURadio”
https://jeremyclark.ca/wp/telecom/plutosdr-for-433mhz-70cm-lna-testing-on-gnuradio/

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.