DBK
LIFE MEMBER
In this thread
https://www.motorhomefun.co.uk/foru...rcraft-with-a-raspberry-pi-and-an-sdr.219017/
I mentioned that I'd only got involved with tracking aircraft because I was having a few teething troubles with what I was really trying to do which was to receive weak radio signals from as far away as possible. Well, it fills in a bit of Lockdown time.
The technology I was trying to get to work is called WSPR which stands for Weak Signal Propagation Reporting and it is pronounced "whisper" which seems appropriate as these signals can be incredibly weak. I'm not sure what the record is but transmissions of just a few mW can be heard thousands of miles away - if you have the right antenna - more of which later.
The system was invented by a very bright bloke in the US who had previously won a Nobel Prize - although not for WSPR I think. The transmissions operate in the HF band and consume a tiny amount of bandwidth. A popular frequency is in the 20m band and operates at 14.095,600 MHz and occupies at that frequency just 200Hz of bandwidth. Each transmission takes up even less as it changes up and down over just 6Hz over a two minute period to send the packets of data.
Here is the equipment I am using.
The silver thing in the upper right is a software defined radio (SDR) dongle which plugs into my PC with a USB cable. The blue box was what I needed to get this to work. Many have been able to do this without one but I think because of where I live and the difficulties of raising a good antenna here I found it essential to pick up any signals. The problem is the £30 SDR isn't designed for HF frequencies, they are too low. What the blue box does is adds 125 MHz to the signal so it falls into the range the SDR can work with. You can buy SDR dongles which will work directly in the HF band but they are £150 upwards. The blue box is called an up-converter and is powered from a USB battery pack as this apparently gives less noise than using a normal mains powered phone charge.
In the upper left is a thing call a Balun to which are attached two 5m long wires. These are the antenna and form a dipole. Others have got results just attaching a long wire directly to the SDR but this didn't work for me but I will try it in a week or so when another bit of kit called an "Unun" arrives which is specifically designed for long wire antenna.
This is how I'm using this.
The up-converter and SDR are just inside the window the Balun pokes outside.
One wire goes to an upstairs window.
Probably a bit hard to see but it runs from a third of the way down the right hand side of the photo to the open window. The other wire is at right angles to it and runs to the top of a wooden fence.
The clever stuff is on the PC. The SDR is controlled by a free program called SDR# although there are others available. Here's shot of it working.
The large blue part of the image is known as the waterfall and it shows what signals are being received. If you look carefully you may see a white streak running from top to bottom. This is a WSPR signal and it is barely discernible from the background noise.
The really clever stuff is the program which takes this noise saturated signal and separates out the WSPR data. The free program which does this is called WSJT-X and it was written by the Nobel Prize winning bloke. When you launch it two windows open up. One shows the WSPR signals.
Each of those vertical bands are examples of the two minute long WSPR signals. They are not all vertical because my cheap SDR drifts a bit, especially when first switched on until it has warmed up. If you look at the top of this image you may see a feint green line between 1400 and 1600. This is the 200 Hz wide window the WSPR signals need to be in. By tweaking SDR# the signals can be moved into this band. If you look at the SDR# screenshot you can see a ticked box called Shift and opposite this you enter the Up-converter's addition of 125 MHz but it is possible to slightly alter this to bring the WSPR signals into the sweet spot they need to be, which is why it shows -124,999,940 and not -125,000,000. This is arrived at by trial and error. SDR# has another way of doing this but the jumps were too big. Altering the Shift was more gradual.
The other window WSJT-X displays has the decoded WSPR signals.
In the bottom right is a green bar showing 34/120 this bar moves during each two minute window and in the last few seconds decodes any transmissions received. It can handle multiple signals at the same time. The text which fills the main part of the window are the WSPR signals and for an beginner like me the main bits of data of interest are the last one, which is the distance the signal has come from in kilometres and the Call sign and Grid of the sender. You can feed any of these into a website and it will show you with varying degrees of accuracy where the signal originated. Near the bottom is one from 1779 Km away and entering the call sign of HA6QL into this website shows it came from east of Budapest.
It is possible to receive WSPR signals in Europe from North and even South America but that needs a better antenna than I've got at the moment.
https://www.motorhomefun.co.uk/foru...rcraft-with-a-raspberry-pi-and-an-sdr.219017/
I mentioned that I'd only got involved with tracking aircraft because I was having a few teething troubles with what I was really trying to do which was to receive weak radio signals from as far away as possible. Well, it fills in a bit of Lockdown time.
The technology I was trying to get to work is called WSPR which stands for Weak Signal Propagation Reporting and it is pronounced "whisper" which seems appropriate as these signals can be incredibly weak. I'm not sure what the record is but transmissions of just a few mW can be heard thousands of miles away - if you have the right antenna - more of which later.
The system was invented by a very bright bloke in the US who had previously won a Nobel Prize - although not for WSPR I think. The transmissions operate in the HF band and consume a tiny amount of bandwidth. A popular frequency is in the 20m band and operates at 14.095,600 MHz and occupies at that frequency just 200Hz of bandwidth. Each transmission takes up even less as it changes up and down over just 6Hz over a two minute period to send the packets of data.
Here is the equipment I am using.
The silver thing in the upper right is a software defined radio (SDR) dongle which plugs into my PC with a USB cable. The blue box was what I needed to get this to work. Many have been able to do this without one but I think because of where I live and the difficulties of raising a good antenna here I found it essential to pick up any signals. The problem is the £30 SDR isn't designed for HF frequencies, they are too low. What the blue box does is adds 125 MHz to the signal so it falls into the range the SDR can work with. You can buy SDR dongles which will work directly in the HF band but they are £150 upwards.
The blue box is called an up-converter and is powered from a USB battery pack as this apparently gives less noise than using a normal mains powered phone charge.In the upper left is a thing call a Balun to which are attached two 5m long wires. These are the antenna and form a dipole. Others have got results just attaching a long wire directly to the SDR but this didn't work for me but I will try it in a week or so when another bit of kit called an "Unun" arrives which is specifically designed for long wire antenna.
This is how I'm using this.
The up-converter and SDR are just inside the window the Balun pokes outside.
One wire goes to an upstairs window.
Probably a bit hard to see but it runs from a third of the way down the right hand side of the photo to the open window. The other wire is at right angles to it and runs to the top of a wooden fence.
The clever stuff is on the PC. The SDR is controlled by a free program called SDR# although there are others available. Here's shot of it working.
The large blue part of the image is known as the waterfall and it shows what signals are being received. If you look carefully you may see a white streak running from top to bottom. This is a WSPR signal and it is barely discernible from the background noise.
The really clever stuff is the program which takes this noise saturated signal and separates out the WSPR data. The free program which does this is called WSJT-X and it was written by the Nobel Prize winning bloke. When you launch it two windows open up. One shows the WSPR signals.
Each of those vertical bands are examples of the two minute long WSPR signals. They are not all vertical because my cheap SDR drifts a bit, especially when first switched on until it has warmed up. If you look at the top of this image you may see a feint green line between 1400 and 1600. This is the 200 Hz wide window the WSPR signals need to be in. By tweaking SDR# the signals can be moved into this band. If you look at the SDR# screenshot you can see a ticked box called Shift and opposite this you enter the Up-converter's addition of 125 MHz but it is possible to slightly alter this to bring the WSPR signals into the sweet spot they need to be, which is why it shows -124,999,940 and not -125,000,000. This is arrived at by trial and error. SDR# has another way of doing this but the jumps were too big. Altering the Shift was more gradual.
The other window WSJT-X displays has the decoded WSPR signals.
In the bottom right is a green bar showing 34/120 this bar moves during each two minute window and in the last few seconds decodes any transmissions received. It can handle multiple signals at the same time. The text which fills the main part of the window are the WSPR signals and for an beginner like me the main bits of data of interest are the last one, which is the distance the signal has come from in kilometres and the Call sign and Grid of the sender. You can feed any of these into a website and it will show you with varying degrees of accuracy where the signal originated. Near the bottom is one from 1779 Km away and entering the call sign of HA6QL into this website shows it came from east of Budapest.
It is possible to receive WSPR signals in Europe from North and even South America but that needs a better antenna than I've got at the moment.
Last edited:
