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Tracking Using a SDR

This is incomplete.

Needs antenna advice


With recent advances in software defined radio (SDR) it is in theory possible to track and listen into a payload using a sub £20 dongle and your PC. This is cutting edge and although suitable for testing and tracking the payloads of others it isn't recommended for actual tracking and recovery of your own payload. DVB-T dongles based on the Realtek RTL2832U can be used as a cheap SDR, since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation.

The RTL2832U outputs 8-bit I/Q-samples, and the highest theoretically possible sample-rate is 3.2 MS/s, however, the highest sample-rate without lost samples that has been tested so far is 2.8 MS/s. The frequency range is highly dependent of the used tuner, dongles that use the Elonics E4000 offer the widest possible range (64 - 1700 MHz with a gap from approx. 1100 - 1250 MHz).

WARNING : It is unlikely you will be able to use these devices for tracking a real flight unless you have a very good antenna. However for bench testing payloads they are more than adequate.

Note on Antennas

For testing all that is really needed is a piece of wire 164mm (1/4 the wave length of a 434Mhz signal) pushed in the end of the dongle. A small 433/434Mhz stub antenna screwed in the end will also suffice. Neither of these will allow you to track real flights unless they are extremely close.

Compatible Devices

The thing to look for is the tuner the SDR uses :

Elonics E4000 52 - 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)
Rafael Micro R820T24 - 1766 MHz
Fitipower FC001322 - 1100 MHz (FC0013B/C, FC0013G has a separate L-band input, which is unconnected on most sticks)
Fitipower FC001222 - 948.6 MHz
FCI FC2580146 - 308 MHz and 438 - 924 MHz (gap in between) NOT SUITABLE FOR HAB

Data sourced from The E4000 is hard to get hold of these days to the one you should be going for are R820T based boards. Some of the earlier boards lacked the anti static protection to allow the use of these with larger antennas.

Warning. I don't know if mine is broken but its totally useless at receiving actual in the air HABs. Ok for testing but it drifts badly too. I would appreciate anyone else who has uses these giving some feed back thanks - Upu The NEWSKY TV28T RTL 2832U / R820T is a extremely cost effective unit that comes with an SMA adaptor. Older versions of TV Dongles do drift however more recent (2015) versions are much better and are used by many people for tracking. Dedicated dongles such as Airspy are now much more common and form the basis of very good receivers.

Mac Software

Gqrx SDR receiver has been successfully used with a the ezcap USB 2.0 DVB-T/DAB/FM dongle with good results.

Windows Software Installation

Data sourced from

You will need :

1 x compatible dongle. Author has tested the ezcap USB 2.0 DVB-T/DAB/FM & a NEWSKY TV28T dongle with good results.

SDR Software Installation

The guys at SDRSharp have done a very easy script for installing the dongle. Go to :

Extract this zip and double click Install. This will create a sub directory called sdrsharp. Within this sub directory double click zadig.exe and you will see the following with an empty list :

Click on options and select “List all Devices”

Choose the one that says “Bulk-In Interface (Interface 0)”.

In the box on the right of the green arrow ensure WinUSB is chosen. Check the USBID matches one of the devices in the list above. Click the button that says “Replace Driver”.

Run sdrsharp.exe and you will see the following window:

Check WFM
Next to the PLAY button drop the box down and select RTL-SDR / USB
Amend the VFO Frequency to 98,000,000
Press Play

If you have it selected correctly you will see something like the following. Each of those large peaks on the waterfall are commercial FM radio stations. Put your red cursor over one and click. You should be able to hear the station.

The big spike that's always present in the middle is the DC Offset and can be ignored.

Listening for a Payload

Due to the huge bandwidth of the dongles you can seem pretty much the whole frequency range the payloads operate on in one fell swoop, however sometimes this does make locating the payloads in all the noise difficult.Amend the VFO frequency of the dongle to 434,500,000 and the mode to USB.

You should now see something like this :

Now turn your payload on. You should see a spike around the frequency of your payload :

Click near to this with your cursor, then zoom in slightly, the reposition your cursor over the top of the peak :

At this point you should be hearing the RTTY from your payload. You can zoom in / amend filter bandwidth to get it spot on the frequency. You can increase the resolution to make the waterfall and spectrum analyser less blocky.

Decoding the Payload

For the next step you will need to download and install Virtual Audio Cable or some other such software.

Some sound cards under Windows support “Stereo mix” which is a built in feature to perform this function for you. Enable it following these instructions:

If not, chose one of the below pieces of software.

Virtual Audio Cable is available here : Virtual Audio Cable demo send some voice over the channel saying “TRIAL” so it's pretty useless now for this use.

VB-CABLE Driver:, (21/08/18 Now moved to here: VB-Cable driver is a donationware. The configuration steps are the same than VAC. You should try this one.

Jack Audio is availble here :

Install it and just accept the defaults. Now go into Control Panel → Sound → Recording.

You should see an input called Virtual Audio Cable, click properties and rename it to SDR. Click on listen and check the Listen to This Device option :

Stop SDR# and under Audio select Output Line 1 (Virtual Audio Cable) Click start, you should now be able to hear the payload still.

Now open DL-Fldigi, click Configure → Sound Card Click Capture → SDR(Virtual Audio Cable)

You should now be able to click on the payload as normal and decode :


Installing the new driver will stop the EZCAP from being seen by the supplied radio/TV software. The quickest solution is to just plug it into a different USB socket when you want to use it for that, and re-insert in the original socket for tracking.

guides/sdr_tracker.txt · Last modified: 2018/08/21 12:57 by kevwal

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