NanoVNA for 433MHz/70cm BPF+LNA Testing

Introduction

In the previous two posts I tested a 433MHz LNA for its frequency response or S21. I first used a PlutoSDR signal generator and then a NanoVNA (Ref.1/2). In this post I will add a BPF Band Pass Filter and examine the response of the BPF+LNA using the NanoVNA.

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 BPF + LNA with the 10dB attenuator connected to the RFin of the BPF and the 20dB attenuator connected to the RFout of the LNA. 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 filter/amplifier to be a filter with response of -10dB + Gain(Filter-Amp) -20dB = -10 + 21 -20 or approx -9dB at the band pass frequency. 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
Fig.5 S21 LogMag with 433MHz BPF + LNA
Fig.6 S21 LogMag 433MHz BPF

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. Figure 5 shows the attenuation of the BPF + LNA with a loss of -9.2dB at 436MHz. This indicates the filter has an insertion loss of about 2.2dB in the passband. Figure 6 shows S21 for the BPF alone.

Fig.7 YouTube Video “NanoVNA for 433MHz/70cm BPF + LNA Testing”

References

#1. – “NanoVNA for 433MHz/70cm LNA Testing”
https://jeremyclark.ca/wp/telecom/nanovna-for-433mhz-70cm-lna-testing/

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

#3. – “NanoVNA Related Blog Posts”
https://jeremyclark.ca/wp/blog-legend/


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.