Software Defined Radio SDR BY DON GIBSON KJ

Software Defined Radio - SDR BY DON GIBSON KJ 6 FO@SQUIRRELENGINEERING. COM

What is SDR? • Software Defined Radio is about building radio functions using software in place of traditional hardware circuits. • SDR is NOT a “mode”. • SDR IS a different approach to building a radio and the ability to take advantage of the unique abilities of computer HW/SW.

SDR is not new Conceived back around 1970 at TRW under Do. D program. Until recently SDR was cost prohibitive. • Most of today’s PC computers are up to the task. • DSP chips now affordable. Some SDR functions are also built into modern (Ham) radios. Ex. IC-7300, not a full SDR radio. A Hybrid. The math is over 200 years old. Joseph Fourier 1768 – 1830

Traditional radios have specialized circuits – SDR uses generic circuits. Modes like AM, SSB and FM each have specific circuits that only work for that mode. Filters, Limiters, BFOs Oh my! SDR uses computing software and chips to handle these functions. The digital hardware is very general purpose, not requiring different circuits per mode. DACs, ADCs, CPUs.

Functions are done in software A new mode/function is implemented in software. The SDR is controlled by computer. Computers can add unique functionality to the radio system. Ex. Mixing data and voice. Adding logic to a radio system Ex Scanning, Freq Hopping, ? ?

SDR advantages over traditional radio Some things just cannot be done easily in hardware but can be done easily in software. Example: Filters. Complex In to build hardware that works well and tends to be very specific. software it is just “Math”. (Fast Fourier Transform) Super tight filters that can be adjusted over a very wide range (Will see in demo soon) 10 s of Hz to Khz Can completely remove an interfering signal(s). Manual or automatic. Could be done in HW with dedicated & expensive filters, but not as adjustable. Multiple filters require multiple HW. Filters in SW are limited only by computing resources. More filters than you probably need.

SDR advantages – cont. SDR can “see” wide swaths of spectrum at the same time. • Traditional radios “see” of 3 KHZ (Audio Bandwidth) at a time. • SDRs can see multiple MHZ at a time. 2 - 10 Mhz is typical. • Example to the left is entire 40 M band! (only 300 Khz) • The red line & shading, is what a traditional radio would see. • This allows you to see the entire situation and signals you would never see on traditional radio.

SDR advantages – cont. The spectrum display & waterfall. Most SDR programs do this in some form. Example of intermittent activity. Data Burst SSB Voice.

10 Mhz view! Red line is KFI 640 WWV at the right edge Notice the diagonal line? Ionosode

Another example of an Ionosode signal

Example of rapid signal strength variation. 15 Mhz around 7 AM, band is opening up but not open.

Three easy and cheap ways to get into SDR. The SDR Dongle – Very cheap. Does a lot! More moderate priced SDRs – More function & better performance. Web. SDR – Free and very useful Many other SDRs out there. I will focus is on receivers tonight. Xmit is also possible.

Typical RTL-SDR Dongle

The SDR Dongle – Aka RTL Dongle” Based on an USB European TV receiver “dongle”. Uses the RTL 2832 U chipset. Hence “RTL” Hacked to be an SDR (Early 2010 s? ) Very affordable Lots of variations but all mostly the same. Typical cost $20 -ish. Complete Kits w Antenna around $30 All cover VHF-Lo through Microwave up to 1. 75 Ghz. Some also cover the HF bands. 2 Mhz bandwidth Connections USB to computer – Data and power SMA antenna connection.

Software Free software! Windows, Mac, Linux, Phones Popular programs SDR# HDSDR SDRConsole Specialized Apps ADSB – Tracking aircraft WX Satellite Radio astronomy Lots More!

So cheap you can dedicate them to a function. I use an RTL dongle and a Raspberry PI full time to monitor my home weather station.

A more intermediate SDR - SDR Play

SDR Play More expensive but much better performance Multiple models range from ~ $100 to $300 Low priced models are very good. Higher price models have more exotic features. 10 Mhz bandwidth Software SDRUno – complex, very powerful (Free) Most of the other software can run with these devices. Pick one you like. Connected by USB and SMA Antenna

Web. SDRs – SDR on the web

Web. SDRs Not a single “thing” Multiple websites – different user interfaces Advantages are: Totally FREE! Use remote locations to listen from elsewhere. Very handy when local noise is high or propagation is bad in your local area. Great You for listening to HF Nets. Hear more stations. can “Hop around” the world. UI can be clunky.

More and More SDRs available Transmit Tend versions to be expensive $1000 s Flex Radio Hack I RF – Cheaper, but low power. don’t have a zero experience with SDR xmit Most of the “cool” is in receivers. Hams mostly use known modes and SDR XMIT has less advantages (My opinion, Your mileage may vary)

SDR Play – DEMO TIME

73 s de KJ 6 FO@Squirrel. Enginerring. com Blog: Squirrel. Engineering. com