onsdag den 12. februar 2020

2 GHz Spectrum Analyzer with SDRplay

SDRplay RSP1A can be used as a spectrum analyzer between 1 kHz and 2 GHz. "RSP Spectrum Analyser" is free Windows software developed for this purpose. "RSP Spectrum Analyser" can be downloaded from the SDRplay website.

Figure 1. SDRplay RSP1A with a 20 dB attenuator.
I wanted to test a Pierce crystal oscillator. The circuit diagram is shown in figure 2. I've built the oscillator on a piece of Veroboard using leaded components. The crystal frequency is 7.030 MHz.

Figure 2. Pierce crystal oscillator.

Figure 3. Measuring the crystal oscillator.

The different items are connected as shown in figure 3. A is the crystal oscillator. B is an active probe; it has no amplification but Zin is 10 Mohm and Cin is 0.5 pF. C is a 50 ohm coax cable. D is an 20 dB attenuator. E is SDRplay, and F is the USB-cable connecting SDRplay to a Windows PC.
Figure 4. Screen-dump from RSP Spectrum Analyzer.
The screen-dump in figure 4 shows a 5-25 MHz sweep. On the vertical axis, the reference level is 0 dBm and the lowest level is -80 dBm. Spike A is the fundamental frequency, C is the 2nd harmonic at 14 MHz and E is the 3rd harmonic at 21 MHz. The remaining spikes are B, which is a spurious signal, D is a real signal, and F is a spurious signal from the SDRplay clock at 24 MHz. Spike F can be removed be activating "clock spur removal".  

Another example is measuring a band-pass filter for 1090 MHz. I connected a noise generator in front of the filter in order to create an input signal. The RSPplay was connected to the filter's output, and no attenuator was used this time (the noise signal is weak and should not be attenuated). 

Figure 5. Measuring a band-pass filter.
The reference level in figure 5 is -40 dBm, and the lowest level is -120 dBm. The sweep is 1000-1200 MHz. The filter curve is clearly visible. 

I've had much fun running SDRplay as a spectrum analyzer. The RSP Spectrum Analyzer software works excellently. For the radio amateur and the hobbyist, SDRplay is an acceptable alternative to dedicated (and expensive) spectrum analyzers!

73 from OZ1BXM Lars
Homepage: http://oz1bxm.dk/

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