Filter measurements with RF noise source

I got my BG7TBL RF noise source to make some RF measurements. To make those measurements, I needed some instructions how to make them. I first started with filter measurements because I could make them with the devices I have. Two good tutorials for doing measurement are Measuring Filters and VSWR With RTL-SDR and RTL-SDR Tutorial: Measuring filter characteristics and antenna VSWR with an RTL-SDR and noise source. There are also useful video tutorials:

KF5OBS #33: Filter Measurement using Noise Source

Using the BG7TBL Noise Source to Characterize a HF Filter

Now to practical testing. In addition to noise source the other tools I used were RTL-SDR compatible USB DVB-T stick and Spektrum RTL-SDR Spectrum Analyzer Software. Spektrum software with my RTL-SDR stick gave quite nice results, even though RTL SDR Dongles have somewhat anomalous frequency domain response.

Testing results (measured about 170 MHz band pass filter, cheap surplus I do not have data for)


End verdict is that measurement works acceptably. Doing measurements on wide frequency range is quite slow (take tens of seconds for one scan) and there is quite limited dynamics compared to expensive commercial measurement tools like vector network analyzer or spectrum analyzer with tracking generator.

2 Comments

  1. Tomi Engdahl says:

    Classifying Crystals With An SDR Dongle
    https://hackaday.com/2018/06/06/classifying-crystals-with-an-sdr-dongle/

    When it comes to radio frequency oscillators, crystal controlled is the way to go when you want frequency precision. But not every slab of quartz in a tiny silver case is created equal, so crystals need to be characterized before using them. That’s generally a job for an oscilloscope, but if you’re clever, an SDR dongle can make a dandy crystal checker too.

    RTL-SDR USB receiver – cheap tool for matching crystals
    https://www.youtube.com/watch?v=F6pNEsxSvHQ

    working on my home made HF 6-band SSB transceiver and this little thing helped me to made 8MHz IF filter. It also helped me in company with wide band noise generator to tune front-end bandpass filters.

    Reply

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