Small Software Defined Radios — Part 1: Hardware

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The SDR Stick

The workshop will concentrate on the USB stick style SDR. The most popular is probably the RTL-SDR unit based on the DVB-T TV tuner and the RTL2832U chipset. Sure it can be used to decode digital TV, but some innovative soul recognized that it could also be a general purpose receiver with a range of about 25 MHz to 1.5 GHz. Figure 1 shows that USB device along with a kit of handy parts to get started. This is available from Amazon here for about $28.
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Figure 1. The starter kit for the RTL-SDR

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Figure 2. Inside the RTL-SDR stick

With this and your computer you can have a bunch of fun and learn about pan adapters, SDR tuners, and even watch for aircraft data.

Antennas for the Sticks

The starter kit comes with collapsable whips, a suction cup mount, a small lightweight tripod mount, and feed line. You can do quite a bit with just these parts. If you wanted to use this for a particular purpose (like monitoring aircraft) you can get an antenna specifically for that band or frequency. For example, this antenna is used for doing ADS-B aircraft monitoring. It is available from Amazon here for $8
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Figure 3. ADS-B monopole

Then again, you can make your own antennas easily enough for this purpose or others. See another article I wrote Homebrew ADS-B Antenna for Airplane Tracking for more information on that.

It is possible to use an existing antenna as well. The RTL-SDR dongle accepts an SMA type connector. A converter from SMA to BNC can be handy. Amazon has a set of two here for $11. See Figure 4.
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Figure 4. SMA to BNC connectors

No Computer? No Problem!

An excellent way to explore these small SDR devices is with an inexpensive Raspberry Pi computer. I recommend getting one of the higher end models of these single board computers with a little extra horsepower. Processing SDR signals takes a lot of CPU power and that generates heat. My first Raspberry Pi unit was underpowered and it overheated within minutes. I’ve switched to a newer and faster model that handles the task easily. And, I’ve put it in a case with a small fan to increase airflow. See Figures 5 and 6.
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Figure 5. Raspberry Pi 3 B+ motherboard

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Figure 6. Kit with case, power supply, and heat sinks

These two items are available from Amazon. The Raspberry Pi 3 B+ board is $39 here. The kit that includes a case, fan, heatsinks, and power supply can be found here for $16.

Amplifier

A small device called an MMIC is a broadband RF amplifier that can bring signals up 30 dB. One of these is available on Amazon mounted on a board with two SMA connectors (in and out) here for $11. See Figure 7.
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Figure 7. MMIC amplifier for RTL-SDR use

You’ll also need a jumper to go between the amplifier and the SDR. An SMA to SMA jumper (set of 2) is available here for $4.59. See Figure 8.
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Figure 8. SMA-SMA jumper

Aircraft Tracking

If you enjoyed the aircraft tracking talk given in the regular meeting by Thomas R Kavanaugh, KC1ELF, then you might be interested in the SDR stick sold by Flight Aware specifically designed for this purpose. It has an amplifier built in, and a filter centered around the ADS-B frequency. It is available here for $20. See Figure 9.
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Figure 9. The SDR bundled solution for flight tracking