Shrink/Expand Raspberry Pi Filesystem Images

This post documents a few tricks I found useful when making SD card images for Raspberry Pi projects, to minimize file size and download times while making full use of the SD card space. These instructions work for Raspbian Stretch images; not sure about older or newer versions. The first time a Raspbian system boots, it runs a program to expand the filesystem to use the full size of the SD card. So, when you are using a Raspberry Pi […]

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RTL-SDR.com Dongle Measurements (Part 2 — Results)

In Part 1 I described some background about SDR dynamic range as an introduction to the measurements I did on a RTL-SDR.com v3 USB “dongle” SDR. Now for the results. I wrote a Gnu Radio program to help measure the dongle. It tunes the dongle, sets its front-end gain, shows a spectrum display, and also shows the power in a 500 Hz bandwidth around the tuned frequency. That power reading is what I used for these measurements. The flowgraph is […]

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RTL-SDR.com Dongle Measurements (Part 1 — background)

I’m using several USB “dongle” SDR sticks from RTL-SDR.com. These nifty $20 devices can receive from 100 kHz to above 1700 MHz. They have a low noise amplifier in the front end that is adjustable from 0 to about 50 dB gain. I wanted to determine the impact of the gain setting on receiver performance, and the results are below. First, some introduction. The dongles use an 8 bit analog-to-digital converter (“ADC”). The number of bits sets the dynamic range, […]

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