Small Software Defined Radios — Part 1: Hardware

Stacks Image 5

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.
Stacks Image 11

Figure 1. The starter kit for the RTL-SDR

Stacks Image 15

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
Stacks Image 25

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.
Stacks Image 31

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.
Stacks Image 39

Figure 5. Raspberry Pi 3 B+ motherboard

Stacks Image 43

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.


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.
Stacks Image 55

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.
Stacks Image 61

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.
Stacks Image 69

Figure 9. The SDR bundled solution for flight tracking

November 30, 2018
RapidWeaver Icon

Made in RapidWeaver