So you are in receipt of a shiny new Realtek RTL2832U+R820T SDR dongle and I understand the first thing you want to do is start decoding ADS-B, ACARS or some other exotic data format. Maybe you just want to listen in to some local comms? Well we really need to get some software loaded up.
There are two popular SDR tuning programs and both are freeware: SDR# (SDRSharp) and HDSDR. I’ve tried both, but highly recommend SDR# as its more user friendly – especially for newcomers so we’ll stick with that.
There are numerous SDR# versions available (stable/nightly builds) and a degree of experimentation is required to get the program up and running. Installation worked flawlessly on one PC but was a total nightmare on another. Eventually I got it working on both (funnily identical Windows XP platforms!). SDR# requires .NET Framework to be installed prior to running and the problems I had installing SDR# on my laptop was because I had 4.5 installed and not 3.5. To be on the safe side I ended up installing .NET Framework versions 1.0, 2.0, 3.5 and 4.5 (overkill or what?!).
I’m glad I persevered though because SDR# is really good and seems to be less CPU intensive compared directly with HDSDR.
Once installed the user interface is simple to navigate. The latest nightly build version differs from the stable version, but not in a way that will confuse so switching between the two is not a problem. In addition multiple dongles can be used with SDR# on a single PC.
Before tuning, the SDR needs to be selected from the top situated drop down menu. If installation was successful (fingers crossed!), “RTL-SDR/USB” should be available (if its not there, or just “RTL-SDR/TCP” appears, its back to the drawing board I’m afraid as (probably) some .dll files are missing or the configuration file needs tweaking).
The most common route to ensure everything is working is to tune to a known FM broadcast in the 88-108 MHz range. Select WFM from the Radio menu, Filter Bandwidth 48,000, 100kHz tuning step, check the FM Stereo box and then using your mouse scroll to find a local station. When I first tried this I thought my dongle was bit deaf as the signal was very weak. Then I noticed the “Configure” button next to the VFO.
Here you can adjust the dongles RF Gain using a slider and also change the MSPS sample rate and fix the dongles output frequency to match the VFO with Frequency correction in ppm (I have two dongles and one is set to 57, the other to 78, so the accuracy varies quite a bit). Incidentally, don’t adjust the ppm until the dongle has warmed up as the frequency oscillator has a tendency to drift until the working temperature has settled down. Configuration needs to be done before pressing the “Play” button though RF Gain can be adjusted anytime.
As default SDR# opens up the dongle in a 0dB RF Gain state so that is where my initial issue stemmed. I cranked up the RF Gain and signals started booming in.
The main display is dominated by two size selectable windows – the top is the Frequency Analyzer which can also display peaks via the Radio menu (Mark Peaks) and beneath that is a Waterfall essential for honing in on data signals. To the right of the display three vertical sliders control Zoom (frequency zoom), Contrast (resolution) and Speed (the speed with which the waterfall scrolls). Additional settings are displayed in the left situated FFT Display menu. I’ve found the default settings to be fine so far and have my resolution set to 32768 which is a good compromise for both visual appearance/usefulness and CPU loading.
SDR# also features a great Frequency Manager plugin. Here you can enter and save frequencies, modes and filter bandwidth and save them in folders for ease of use. You can also record any transmissions received with the Recording plugin.
SDR# is a really well thought out program and it works perfectly.
Of course the higher the sampling rate the more your PC will moan and groan so be careful. When tinkering with settings its a good idea to write down optimum parameters otherwise its all too easy to get confused with what works or doesn’t.
If I gave ratings I’d give SDR# a 5/5! It lacks a notch filter (HDSDR has one) but I understand that the author of SDR# is working on it. It’s not something I personally require but I know some users have requested it.
Another piece of interesting freeware that came via the SDR downloads page was ADSB#, an open source ADS-B decoder – this is a standalone interface and doesn’t require SDR# to run in the background. ADSB# doesn’t require manual tuning either as it automatically tunes to 1090.000MHz all by itself.
There are just a few settings to deal with. Set the “Confidence” level to “4″ (the higher the setting the more accurate the results) and leave the “Timeout” at 120 seconds. Port output is preset to 47806 for use in other program network settings. The RF Gain can be set manually (RTL AGC) or automatically (Tuner AGC) according to requirements. Frequency correction can be adjusted when known (ascertain this from tuning in SDR#) or leave as is, as ADS-B signals are a generous 2 MHz wide at 1090.000 MHz, (minor inaccuracy is therefore irrelevant).
ADSB# is a decent decoder giving excellent framerates and reliability. This was the first decoder I used with adsbScope and due to their (relative) simplicity ideal for beginners
Another decoder and probably the most popular is RTL1090 from rtl1090.com. There are currently two versions available at the moment Build 100 and Build 102 (recently upgraded from beta 2). Both are freeware and more advanced and developed than ADSB#. The 102 version is the more sophisticated of the two and PlanePlotter requires that all validated Ground Stations use that build due to the raw data requirements utilised for multilateration (or Mlat for short).
There are additional settings under configuration some especially for use with PlanePlotter such as Home Location and Station ID. As with ADSB# once the chosen program (e.g. PlanePlotter) is set up to receive the decoded data they are autonomous and don’t need any further attention. RTL1090 is also good for Mode-S and Mode AC, provides USB packet info and II/SI radar data.
RTL1090 (Build 102) is my go to decoder, however it does have a tendency to freeze-up randomly on my Windows XP setup. I’ve not really got to the bottom of it. I have disabled USB selective suspend on all my computers, turned off all power saving features on my laptop, but it still happens every other day or so (I run a 24/7 PlanePlotter Ground Station). Loose connections between the dongle and USB extension have caused a few hiccups and it may well just be that (insulation tape is probably the answer!). If I find out why this happens I’ll update this post.
adsbScope is the only freeware virtual radar program that gives a feel for some of the more advanced shareware models. I started using adsbScope the day I got my first dongle and highly recommend it to anyone with an interest in ADS-B – download this before progressing to premium programs. Like I say, its 100% free, no nags and works exceptionally well with either ADSB# or RTL1090. Its intuitive (up to a point) and I had mine running within an hour (that said, I did take the dog out for a walk mid way through the set-up to clear my head!).
A couple of pointers. To setup using either ADSB# or RTL1090 head to the menu: other>Network>Network setup and select the appropriate program from the RAW data client section. The port will be automatically assigned 47806 for ADSB# and 31001 for RTL1090. Then back to the main screen – click the “start raw data client” button (its the 11th from the left) which should illuminate red. The map display shoud start to populate and the table to the right duplicates what is shown graphically, but in more detail. The graphic output is customisable so spend a few hours adjusting what is shown and changing colours to suit. The data table can also be extended to view additional information about the aircraft received. The maximum range feature is useful to determine how good your antenna location is so be sure to check that out.
I really like adsbScope. It has a few short comings, you won’t see any Mode-S military aircraft (though they do appear in table format) and it doesn’t use a sophisticated database, but that said it does come with a decent starter list (text file full of current ICAO hex codes registration tie-ups). Browse through you adsbScope folders (wherever they were downloaded) to find the icao24plus.txt file and open it in notebook to add, delete or amend records. I also like the way the vector maps adjust automatically during zooming with no need to manually write a new map each time. If only it had a shared server network…
Talking of network based ADS-B… that will be covered by my next project. Having looked at what freeware has to offer the time has come to fully explore the powerful features that PlanePlotter provides. I’m sure this will be a long one (!) so hang in there while I piece it all together!