Tracking High Altitude Balloons using SDR

After the talk last night I took a moment to mention my friend Sam Sully, who is running a club at Monmouth School to launch 8 High Altitude Balloon’s (HAB) into the upper atmosphere. The club is involving 42 students from the ages of 12-18 who have been working in teams to build payloads for their balloons.


The payloads used by the club are based around a Raspberry Pi Zero single board computer, Raspberry Pi Camera V2Radiometrix UHF transmitters (each payload on a different frequency between 434.0MHz and 434.8MHz) and GPS Module. The raspberry pi is responsible for getting the location of the balloon from the GPS and sending the coordinates over the radio using the RTTY protocol.

Receiving Setup

There are a few ways of receiving the radio down-link from the balloons. The easiest method for radio amateurs is to use either a 70cm radio with a computer interface or a software defined radio, such as an RTLSDR dongle which many of the club members already have.

In terms of antennas, the clear line of sight provides a relatively easy job. For a tracking vehicle a standard mag-mount 70cm mobile antenna will be sufficient, or even a 1/4 wave ground plane ghetto mounted to the roof of your car! For a base station a high gain 70cm yagi would be more suitable to get better range and pick up the balloon from lower altitudes.

A simple ground plane antenna made from some stripped-back RG-117 strengthened with straws. Works a treat!

An 868MHz antenna built from welding rods and 25mm^2 trunking (this was used for experimental 2-way comms with the balloon and not for tracking)

Software Used

In order to decode the packets from the balloon, the following software is required:

  • SDR# – The first piece of software that I used is called SDR# (SDR-Sharp). It is used to control a SDR dongle, and tune into the frequency transmitted by the balloon payliads. A full guide to installing and setting up the software can be found in one of my previous posts. Download Link
  • VB-Cable – This is a virtual audio cable, used to send the audio from SDR# to the packet decoding software. Download Link
  • DL-FLDIGI – This is the software that decodes the RTTY packets. Download Link

Software Setup

First of all you need to download and install SDR#. Clear instructions on how to do this are provided here

Then you need to set up VB-Cable to send the audio output of SDR# to the RTTY Decoder.

  • Download VB-Cable from the above linkVB-Cable Download
  • Extract the .zip file
  • Run “VBCABLE_Setup_x64.exe” as an administrator (don’t use x64 version if you are using 32bit windows)Running as admin
  • Click on “Install Driver”Install Driver
  • Accept the unverified driver warningUnverified Driver Warning
  • Restart when prompted
  • Go into the sound settings (right click on volume icon, click “sound”)Sound Settings
  • Click on “CABLE Input”, and click on “Set Default”

Now that the virtual audio cable is setup, you will need to is set up SDR#. Tune the radio to the frequency of the payload you plan to receive (these will be posted at a later date), and set the mode to USB. You can adjust the squelch control but that is not required. Set the bandwidth to around 10khz.

Now, your SDR# window should look something like this (except tuned into the 70cm band):

SDR# Windows

Finally, open dl-fldigi (HAB Mode), which decodes the RTTY packets.

You will need to do several things:

  • Select the appropriate audio input (“Virtual Audio Cable” or “CABLE Input“)
  • Move the red markers until they are overlapping the two RTTY signals. After you have done this once the software will automatically track the signals.
  • Select “Op Mode” from the toolbar at the top, then hover over “RTTY” and click “Custom

In this window you must alter these settings:

Carrier Shift => Custom

Custom Shift => 450

Baud Rate => 75

Bits per character => 8 (ascii)

Parity => none

Stop bits => 2

A window showing the RTTY Configuration

RTTY Settings

Now go into the “Configure” menu and setup your callsign. This will be displayed on with every upload you submit.

Now the software is setup you should now see text on your screen. dl-fldigi parses this data and uploads it to habhub. Well done you are now contributing to the tracking!




Tracking a balloon

Now that you are picking up telemetry, the habhub tracker will predict the flight path and landing site for the balloon. The chase vehicles will try and get to the landing site to recover the balloon. Please note this is not as easy as it sounds and takes some practice! Laptops are essential and a minimum of two people per vehicle is recommended.


I hope this is an informative article and perhaps enlightens some of you to the world of high altitude ballooning. Please check out which will have some better instructions on it to help get you set up. If you are having issues don’t hesitate to comment below or send me an email.

Hopefully we’ll see some of you at the launch next weekend! I’ll let everyone know on Wednesday which day we’ll be launching.

-Peter Barnes (2E0UAR)

(edit: i’m sorry everyone I clearly can’t spell balloon)

Antenna Maintanance

Yesterday myself, Andrew, Graham, Rex, John and John spent the day at the Chantry renovating the club’s antenna systems.

Our plan for the day was to inspect the existing antenna systems, replace a section of coax between the attic and balun and to install and tune the new 40m dipole.

Condition of existing antenna systems

Existing 40m dipole balun

Existing 40m dipole balun

The overall condition of the existing HF antenna was good, but clearly the self-amalgamating tape has suffered from UV degradation. This doesn’t appear to be a major problem however the antenna has only been up roughly 4 years, so the problem would get worse over time.

A photo of the existing co-linear VHF antenna

Existing VHF Co-linear

While on the roof we also inspected the existing VHF antenna. It is clear that it is not ideally placed, being blocked by the chimney stack as well as the Chantry’s satellite dish.

Replacing the coaxial cable

One of the jobs for the day was to replace the RG-58 coax run between the attic space and the existing balun with some superior Westflex 103. In order to do this, Andrew and myself had to climb into the attic in order to cut the existing cable and solder new UHF connectors onto it. This allowed us to replace the cable between the attic and the antenna. On completion we measured the loss through the cable using a 50Ω dummy load and power meter.

new cable run

New Westflex 103 cable run

We measured the loss at just under 3dB at 7mHz. We measured 60W at the end of the cable with a 100W input. Currently we plan to improve this loss further by replacing the rest of the cable to the shack

Andrew holding a dummy load and power meter

Andrew getting ready to test the loss through the new cable

Installing and tuning the new 40m dipole

With the new coax installed, we now set to work installing the new antenna. Before we could putt the new dipole in place we had to let down the existing antenna. As the two ends were attached to trees, I volunteered to put my tree-climbing skills to use and lower the existing elements

Rex at the foot of a ladder

Rex giving us a hand getting up the trees

With the antenna on the ground we attached the new dipole and hoisted it into the air. Following some tests with Andrew’s MFJ antenna analyser we deduced that the elements were too long. Following several rounds of tuning we reached a state where everyone was happy with the performance of the antenna.

New 40m dipole balun

New balun installed

We sealed the connections with self amalgamating tape and headed to the shack to have a listen to the band.

40m dipole



Frequency (mHz) Resistance (Ω) Reactance (Ω) SWR
7.0 60 8 1.2
7.1 78 0
7.2 112 0 1.5

We also tested the SWR in the shack and measured an SWR of 1.4 at 7.2mHz. A quick sweep of the band picked up some loud and clear Morse, although this may be due to a contest that was running at the time.


We hope that the new 40m dipole continues to deliver excellent results. There are still improvements that need to be made to the club’s antenna systems, including:

  • Adding the two other elements (30m and 20m) to the fan dipole array
  • Replacing the coax run between the attic and the shack with lower loss cable
  • Deciding on an effective way to relocate and improve the VHF antenna system.

I’d like to thank Andrew G0RVM, Graham, Rex G4RAE, John M3EQQ and John M0HFH for giving up their time yesterday to help the club. I had a great day and learned a lot throughout the process.

Peter Barnes

JOTA 2016 Announcement

This weekend the club is excited to be hosting another Jamboree On The Air (JOTA) event. We will be based at the 1st Olveston Scout hall from Friday through to Sunday. We plan to set up stations covering VHF, HF, SDR, Morse, 3D Printing and more. Over the weekend we are expecting to receive visits from groups of scouts so that we can share our knowledge and experience with them.

We will be operating under the special even callsign GB1OSG for the weekend.

We hope to see plenty of scouts and a club members over the weekend, and i’m sure as usual a lot of experiments (successful or otherwise) will take place during our free time!



Electromagnetic Field 2016

As some of you may be aware, last weekend I went to Guildford to attend this year’s EMF camp. Electromagnetic Field is a camping festival geared towards hackers and makers. The weekend is filled with interesting talks, demonstrations and crazy projects.EMF Sign

Arriving on Camp


My idea of a camping trip!

I arrived on site with a reasonable idea of what to expect, but this was reinforced when someone whizzed past me in a Sinclair C5. This turned out to be only a taster of what was to come.

I was to be joining a group of amateur radio enthusiasts who were running the EMF hams village. There were 16 of us and we had all come with a variety of equipment. Using the special event callsign GB4EMF, we operated using the following stations:

  • HF Station – Yaesu FT-1000, Mosley Mini-33-aw beam, SCAM-12 mast
  • VHF/UHF Station – Icom 706, 2/70 Beam, telescopic mast
  • Satellite Station – Yaesu FT-847, 2 & 70 ZL Specials on G-5500 Az/El rotator, tripod
  • Local Comms – Crossband repeater, Yaesu FT8900, X-50, 5.4m Clansman mast

EMFhams Setup

This was all made easier by the network of datenklos (data-toilets). These were power and networks hubs being kept dry using porta-loos. Over the weekend we maxed out at over 100kW pulled off two generators, 66  Wi-Fi access points, 4500 networked devices and 3.5TB of data going between our network and the internet.


Things to see

There was a lot of ‘stuff’ at EMF this year. A few honourable mentions go to the high altitude ballooning village, fire pong, just add sharks laser cutters, blacksmithing tent, lockpicking tent giant guitar hero, the music powered quadruple flamethrowerretro arcade tent and the amateur radio village of course.

JustAddSharks Laser Cutter

HABville's weather balloon tracking station

HABville’s weather balloon tracking station

Pub sign!

Pub sign!

Overall EMF camp this year was a fantastic event, full of technology and ideas. The talks I attended were very interesting, and all available of the EMF Youtube account. I’m definitely signing up for the event when it next runs in 2018. For more info see,, and for more photos see

View of site

PS: I’ve got my new callsign, 2E0UAR


-Peter Barnes (M6KVA, 2E0UAR)

Receiving Packets from the ISS

One of my main interests in amateur radio involves picking up radio signals from satellites and (one day) talking to astronauts on the space station. Getting a contact with the ISS may be difficult, but there is an easier thing to have a go at first. The space station is fitted with an AX.25 APRS (Automated Packet Reporting System) repeater which transmits on VHF. The repeater is nearly always activated, and sends out packets roughly every couple of seconds.

Hardware Setup

There are several types of hardware setups you can use to pick up the space station’s packet repeater. Handheld yagi antennas are a common choice, and omnidirectional antennas can also be used. Personally I use the following setup:

  • RTL-SDR Dongle (wideband receiver)
  • Crossed Dipole Satellite Antenna

Satellite Antenna


This is the antenna I have been using. It is a 2-element crossed yagi tuned to 137mhz. Originally it was designed to pick up signals from weather satellites, but it receives a good signal from the ISS packet repeater (145.825mhz).

I believe it is also possible to receiving packets from the space station using an omnidirectional antenna. My Kenwood VHF radio was also picking up data packets on a good pass, using a 2m Slim Jim.

The antenna is fed with about 10m of RG-58 coax into the radio shack window. The cable is then plugged into my Realtek Software Defined Radio (discussed in my earlier post) using a MCX to SO259 pigtail adapter.

SDR Setup


Software Used

  • SDR# – The first piece of software that I used is called SDR# (SDR-Sharp). It is used to control my SDR dongle, and tune into the frequency transmitted by the ISS’ APRS repeater (145.825mhz). A full guide to installing and setting up the software can be found in my previous post. Download Link
  • VB-Cable – This is a virtual audio cable, used to send the audio from SDR# to the packet decoding software. Download Link
  • QTMM APRS Decoder – This is the software that decodes the APRS packets. Download Link

Software Setup

First you need to set up VB-Cable to send the audio output of SDR# to the AX.25 Decoder.

  • Download VB-Cable from the above linkVB-Cable Download
  • Extract the .zip file
  • Run “VBCABLE_Setup_x64.exe” as an administrator (don’t use x64 version if you are using 32bit windows)Running as admin
  • Click on “Install Driver”Install Driver
  • Accept the unverified driver warningUnverified Driver Warning
  • Restart when prompted
  • Go into the sound settings (right click on volume icon, click “sound”)Sound Settings
  • Click on “CABLE Input”, and click on “Set Default”

Now that the virtual audio cable is setup, you will need to is set up SDR#. Tune the radio to 145.825mhz, and set the mode to NFM. You can adjust the squelch control but that is not required. Set the bandwidth to around 10khz.

Remember, due to the Doppler Effect, the signal will move as the satellite moves across the sky. You will need to adjust the frequency regularly to compensate for this.

Now, your SDR# window should look something like this:

SDR# Windows

Finally, extract and open qtmm, which decodes the APRS packets. The file that runs the program is called “afsk1200dec.exe

You will need to do two things:

  • Select the appropriate audio input (“Virtual Audio Cable” or “CABLE Input“)
  • Hit the play button

The program should be displaying “Decoder Running” in the bottom corner, like this:


That’s it, all you need to do now is wait for the space station to fly past.

Orbit Tracking

In order to receive data from the ISS, you need to wait until it flies overhead. Enter your locator into Amsat’s Pass Predictor to get a list of passes. You’re looking for something with a maximum elevation as close to 90° possible. At my QTH I get a couple of good passes a day, and have had as close as 89° of elevation.

There is also orbit prediction software available, such as Orbitron, which I have found useful.

I also recommend keeping an eye on an ISS tracker, so you know the exact position of the ISS. The space station also has a high definition camera streaming live, which you  can view from here.

What To Expect

When the ISS flies overhead, you should expect up to about 10 minutes of data reception. On my best attempt, I’ve received data between Cork, Ireland and Frankfurt, Germany. The signals will appear as bursts of digital data, repeating every few seconds or so.

SDR Setup

The decoded data is the raw form of the APRS packets. Some will contain GPS co-ordinates, whereas others will just be CQ calls or messages. Every now and again the ISS will transmit it’s ID, which will appear as “ARISS – International Space Station.”

Here an example of some decoded messages from the ISS repeater:

18:42:27$ fm RS0ISS-0 to CQ-0 UIv PID=F0
>ARISS – International Space Station

18:42:44$ fm EI8ETB-0 to CQ-0 via RS0ISS-0 UI PID=F0
=5151.51N/00826.55W-Thomas IO51SU Cork {UISS54}

Make sure to also listen out on 145.800mhz, the voice downlink used by the ISS. I haven’t heard anything yet, but if the astronauts do use their amateur radio set, it will be on this frequency (145.200mhz uplink / 145.800mhz downlink).


I hope that you have as much luck as myself when trying to receive data from the ISS. If you have any questions then please leave a comment below, or catch me on a club night. I always have my laptop and SDR with me, if you want to have a look.

-Peter Barnes (M6KVA)

Software Defined Radio

The RTL-SDR is an inexpensive software defined radio dongle based on the RTL2832u chipset. The dongle was designed to be used as a digital video and radio receiver, but with some custom firmware can be re-purposed as a wideband software defined radio receiver.

Effectively this means that for under £10, you can get a radio scanner capable of receiving between around 22mhz and 1.8ghz. I started playing around with my SDR long before I became interested in amateur radio, and here are some of my favorite uses:

These are just a few of the capabilities of the dongle. A longer list can be found on the RTLSDR website.

Where to get a dongle

The SDR dongle is available all over the internet, and in a few different versions. The most common one I’ve seen (and the one I use) is listed as RTL2832u + R820T. I bought itfrom Ebay, and it cost me just under £10 at the time.

Here is a link to a search on Ebay, which should come up with the right thing. Ebay search link

The product image should look something like this:

RTL SDR Dongle - Product Image


The SDR dongle usually comes with an included whip antenna for picking up FM radio signals. The dongle has a MCX (Micro Coaxial) connector on it, which can be easily adapted to a SO259 connector (link). Personally I use my dongle with a discone antenna in the loft for general wideband reception, and with a crossed dipole satellite antenna for receiving data from satellites. More information about my antenna setup can be found on my QRZ profile.

Software Setup

The most commonly used SDR software is called SDR# (SDR-Sharp). The installation process is relatively simple, and includes drivers for the dongle. Do not install any of the included software that comes with the dongle.

  1. Download the software from Page
  2. Extract the zip file
  3. Run the “install-rtlsdr.bat” which will download the latest driversinstall-rtlsdr.bat screenshot
  4. Plug in the SDR dongle, and wait for Windows to attempt to install drivers.
  5. In the sdrsharp folder, right click on the file called “Zadig.exe” and select “Run as Administrator”
  6. When the Zadig application opens, click “Options” and select “List All Devices”List All Devices Screenshot
  7. Select “Bulk-In, Interface (Interface 0)” from the drop down list. If RTL2832U or RTL2832UHIDIR show as options, these are also fine to use.Bulk-In sreenshot
  8. Check that WinUSB is shown in the box above “Replace Driver” and then click “Replace Driver.” Your computer may warn you about using unverified drivers, but it is safe to install the drivers regardless.Driver Warning
  9. Run “SDRSharp.exe”
  10. Press the settings button in the top-left corner, and set the gain (requires some experimentation to be set correctly)
  11. Press the play button in the top-left corner

Now SDR# should be set up and functioning correctly. If you have any issues, have a look at the Quick Start Guide, or leave a comment below.

SDR Sharp Guide


This is the SDR# User Interface. In the middle is the Spectrum Analyser and Waterfall, and on the left are all the settings for the program.

Firstly you’ll need to correctly set the gain. To do this, hit the play button in the top left and tune the radio to a frequency with some signals (such as 99.5mhz). Then open the settings menu (cogwheel in the top-left corner) and have a play with the gain control. The correct settings varies from dongle to dongle, but the general advice is to set it as high as you can without noticing an increase in the noise floor.

Using SDR#

SDR# ControlThis is the Radio control panel. It contains the most commonly used settings.

At the top, there is a list of modes that you can select.

Below this are bandwidth, squelch, step size controls.

More information on SDR# can be found on the SDR# quick start guide



I hope this provides you with some useful information about the RTL SDR dongle. It was money well spent for me, as I have used my SDR for loads of different applications, and it was probably the main thing that got me interested in amateur radio. Hopefully you find this guide useful, and if anyone has any questions, just post them in the comments below.

-Peter Barnes (M6KVA)

DIY Wouxun Programming Cable

I use a Wouxun KG-UVD1P handheld radio for all my operations. A few extra features can be used with the addition of a programming cable. These include:

  • Expanding the Tx and Rx range of the radio
  • Programming HAM repeaters into the memory
  • Changing some advanced settings

The cable required currently costs £5.69 from Ebay (link). Looking at the specification of the cable, I decided to look into the option of making one myself.

Parts List


The build process is very simple. Three connections need to be made, as shown in the below diagram.

Circuit Diagram

As I used a 2.5mm to 3.5mm cable, I simply cut it in half, and used a multimeter to match the wires up to the correct connections on the plug. I used some heat-shrink to make everything look nice, and then I was finished. I made sure to check the connections before using the cable.

Image of the cable I madeUsage

In order to use the cable, you need to install a driver, and Wouxun programming software.

  • Download and extract the Windows 8/8.1/10 driver from Prolific’s website (link).
  • Open “Device Manager”
  • You should see “Prolific USB-to-Serial Comm Port” under the “Ports” submenu
  • Right click on the device, and click “Properties”

Screenshot of Device Manager

  • Go to the “Driver” tab and click “Update Driver…”
  • Click “Browse my computer for driver software”
  • Choose “Let me pick from a list of device drivers on my computer”
  • Click “Have Disk”
  • Navigate to the driver that you downloaded earlier, and choose the “ser2pl.inf” file
  • Click “OK” to install the driver

Once that is done, you should be set to go. You can download the Wouxun programming software from their website (link). To program the radio, plug in both headphone jacks, and turn the radio on. Wouxun’s programming software will work automatically and is fairly easy to use.


Despite being slightly harder to set up than the official cable, this DIY option is much cheaper and does the job. Hopefully you find this guide useful, and if anyone has any questions, just post them in the comments below.

-Peter Barnes

Fox Hunting with a TDOA Antenna

In preparation for the pedestrian fox-hunt that happened a couple of weeks ago, I decided to take a look around for some antenna designs that I could build at home. I came across a blog post which showed off a Time Difference of Arrival (TDOA) antenna that someone had designed and built.

TDOA Antenna

A simple and effective fox-hunting antenna

How it works

The antenna relies on a timer, in my case a 555 timer, to generate an audible signal. I have mine calibrated to a frequency of 1kHz. This signal is level-shifted so that it goes between -4.5V and 4.5V. The use of a set of diodes causes the circuit to quickly switch between the two dipole antennas mounted to the unit (tuned to 145mHz). When the signal received by the two dipoles is out of phase, the receiver emits a tone. When the RF source is equidistant from both antennas (when you are pointing at the “fox”) the signals are in phase, causing the tone to disappear.

This design is fully functional regardless of how close you are to the source, providing an advantage over other antenna designs. The audible tone also provides a clear indicator of direction. However, the main issue is the fact that you get two readings, at 180° to each other.

Parts List

The list of components required is quite simple, so I had most of them laying around.

  • 555 Timer
  • 4.7K  Resistor
  • 100K Resistor
  • 2x 470Ω Resistor
  • 2x 0.01uF, 50V Capacitor
  • 10uF, 25V Capacitor
  • 0.001uF, 50V Capacitor
  • 4x 1N4007 RF Pin Diode
  • 2x 10uH Inductor Coil
  • RF Choke, 8 turns (salvaged from a motherboard)
  • SPST Switch
  • 9V Battery
  • 9V Battery Clip
  • Antenna wire (single core) or 4x Telescopic Antennas
  • 1.5M of RG-58 Coax


When building the antenna, I used two blog posts for reference. You can find them here(pdf) and here. For some reason I ended up combining both of the designs, using the design for the dipole circuits, and the design for the rest of the circuit. This probably isn’t advisable, but it worked for me. Here is the circuit I used:

You can test the 555 timer circuit by hooking the output pin up to a speaker. You should hear a tone when power is supplied to the circuit. I started by breadboarding the timer circuit, and then moved it to veroboard for the final build. Once the circuit was complete, I zip tied the PTT button down on my PMR446 Walkie-Talkie, plugged the antenna into my Wouxun KG-UVD1P reciever, and tuned into the 446mHz signal. The antenna worked perfectly first time, providing a clear tone that faded out when I pointed the antenna at the radio.

For the physical construction of the antenna, I used some thick, single core, cable to make the dipole antennas, and mounted the whole thing on a 60cm long piece of wood. Lots of glue gun was used as I couldn’t be bothered to find some screws. I also drilled holes in the ends of the wood to poke the coax through. The dipole elements were attached using screws, and can be bent between a folded and deployed position.


I took the antenna out for the pedestrian fox-hunt that happened a few weeks ago. The antenna picked up the first signal very well, and the audio tone allowed me to find the direction of the transmission to quite a high accuracy. Unfortunately for me, I headed off into the wrong direction, as the antenna will give you two readings at 180° to each other. I had it running all evening, without the battery flattening. The RF choke fell off quite quickly, as I had not done a very good job with the soldering. I was also worried that the connection between the RX input coax and the board would break, so I would consider using a small connector in the future (such as an SMA socket). Overall the antenna worked very well, albeit sending us in the wrong direction! In terms of improvements, I would also like to mount the circuit board properly, and put it in an enclosure.

If anyone has any questions, or wants me to bring mine with me on a club night, just let me know.

-Peter Barnes