Category: application testing


How to receive NOAA satellite signals

Follow Quadrus SDR

NOAA Satellites – Weather maps from space

It’s so fun to track satellites. If you have never tried it, put it on your HAM bucket list. In this post, I give you some info on how to easily do it.

NOAA Satellites are some of my favorites among the best sources of up to date weather forecasts. Understanding weather maps may help you in everyday situations, like figuring out if you need a jacket, a hat, or a scarf on your way to work. The idea is simple, but the equipment needed to receive satellite signals is not trivial.

You’ll need:

The weather in one picture – step by step instructions

I have tested practically all satellite tracking software packages currently available for civilians, and my choice fell on SatPC32. It has been developed by Erich Eichmann, DK1TB, a German ham radio operator and programmer. His excellent software may be used free of charge, although having to put in your geographical coordinates before each start is somewhat uncomfortable. Download here.

After installing SatPC32, you will see the following:


Altogether 12 satellites can be chosen from the available lists – among them NASA sources. Satellite orbit data can be easily refreshed from

There are a number of editable configuration files, among them .sqf files being the most important. The file can be modified by clicking on the question mark in the menu. Notebook starts, and you can see the content of the file plus some advice at the bottom of the ASCII text. Top frequencies for new satellites look like this:




These lines contain the name of the satellite, frequency, mode, and some simple notes. After saving this config file, the software will compensate Doppler shift, and reception will be smooth and continuous.

NOAA Automatic Picture Transmission (APT) is an analogue mode. The data coming from the imaging sensors is used to amplitude modulate a 2.4 kHz sub-carrier, which is then used to frequency modulate the VHF carrier at 137.x MHz. The FM deviation is 17 kHz.

I have heard both NOAA15 and 18 this afternoon (only three NOAA satellites are working). The audio frequency was recorded by Audacity, a well-known software of its kind. A processing software, called WXtoimg, is also needed. Download it from here:


A version of WXtoimg may be used for a while, but it costs a few €.

Reception is possible using the well-known yagi antenna even in horizontal positions, although more sophisticated and expensive aerials may be employed as well. More detailed descriptions may be studied at

The final outcome of my afternoon weather satellite reception was a map like this:


If you take a fancy to try this small and smart satellite hunting project, please share your outcome maps with me and the Quadrus community!

Have fun!

HA6NN, Bandi

If you liked this post, check this out:

Share Quadrus SDR

Direct digital receiver – when HAM radio can save your life

Follow Quadrus SDR

Staying safe with SDR in a hurricane

We Europeans can not imagine how terrible a hurricane can be. Watching the news on TV or surfing the internet, I see several heart-smothering pictures of the destruction caused by storms. Collapsed houses, broken trees, people who lost their homes and all belongings due to something they can not stand up against. I feel deep sorrow for all of them.

These days Patricia - lovely name for a Category 5 hurricane – reached Mexico. According to meteorology experts, she became the strongest hurricane on record, passing both Linda in the eastern Pacific and Wilma in the Atlantic. This morning I was wondering what I could do in a dangerous situation like this.



Keyword is: up-to-date

In case of heavy wind, rain, and extreme weather, the communication infrastructure could brake down. TV, cell network, and commonly used news sources may become unavailable. Without up-to-date news one can not prepare for impending emergency situations. HAM radio has always been the last line of defense for these scenarios. It is independent of infrastructure, and can reach the other side of the globe.

The signals of the disaster recovery forces can be found somewhere around 125-135MHz in the VHF band. This information can be used to warn friends, relatives, or your local community if necessary.

Check out these pages for more useful frequencies:

If you are using a direct digital receiver equipment, like DRU-224 or Quadrus, you can receive VHF and UHF signals not only HF. Thus, you can get the latest news about the upcoming catastrophe from a fail-safe, trusted source. However, you need a pre-selector filter to receive a VHF band in direct digital receiver mode. You can learn more here:

The filter design and layout files are available from here:

The essentials for hurricane news reception

Let’s summarize the basic equipment for a state of the art radio:

  • direct digital receiver
  • pre-selector filter
  • wide band antenna

If you receive something interesting, strange, or amazing, don’t hesitate share with us on our Facebook page!

Stay safe!

Share Quadrus SDR

SRM GUI tips and tricks series – RF record and playback

Follow Quadrus SDR

Hi Everyone,

We at Spectrafold thought it would be helpful for the community if we provided some tips on how to use SRM – even the simpler functions. This is the first piece of this “tips and tricks” or “best practices” series. We are going to look into record and playback this time. Playback and recording will be essential for both amateur and professional SRM use.

For testing purposes I am always using the latest stable release of our software (release 20150415 at this point), which you may get from our support site:

RF Record and playback

Looking into the RF record and playback functionality, one will quickly realize that most of the time we deal with .DSRS binary files (essentially saved samples), which are unique to SRM as an IF file type. I will cover audio recording in a separate post.


We have recorded and shared some IF spectra in a prior blogpost. Feel free to download any of them -  I have chosen 14100+-100KHz-20140316-111835-0984.DSRS, because it has a 200 kHz bandwidth.

You may open and load such a file in SRM by selecting FILE as an input method, then choosing the appropriate file from your hard drive or other location. Start playing it by clicking on ‘Start’.


The user may freely change a number of functions while listening, for example:



You may choose from the following demodulation types:

  1. AM – amplitude demodulation
  2. USB – upper sideband (single sideband) demodulation
  3. LSB – lower sideband (single sideband) demodulation
  4. ISB – independent sideband (or Kahn method) demodulation
  5. FM – frequency demodulation
  6. CW – continuous wave demodulation
  7. IQ – ‘I’nphase ‘Q’uadrature demodulation

If you are using the IF spectrogram (or ‘Waterfall’ as it’s colloquially called), you may want to understand the use of Reference signal strength and the AutoMax/AutoMin functions. You may re-shape the appearance of your waterfall with these, which is very useful to find weaker signals and to separate them from noise more effectively.


Please note that recorded files will be played back continuously and restart unlimited times.


SRM will record into the same DSRS files, which we have discussed at Playback. Firstly, I would recommend to set up a proper folder to save into, which may be done on a per channel basis.


Then you choose the spectrum type in Control -> Recording as shown.

SRM_tips_01_setting_IF_capture_settings_01Recording will start as soon as any source starts feeding data to SRM – just hit the start button. In my case, seen below, I have been generating a known signal with the Internal Generator, to make sure I get the exact same result back.


Saving a spectrum is quite storage intensive: a 1 minute long recording will be approximately 30 MiB with 100 kHz bandwidth. Also, note that due to longer buffering times, your file will appear somewhat later after recording. In my case, it was some 30 seconds after recording stopped. You may close SRM to ensure your file is saved.

The files follow a naming convention:


{filetype IF/AF_channel number-/YYYYMMDD/-/HHMMSS/-/code/}


Feel free to download the SRM-3000 SDR software receiver from the support page and some recorded IF files with different bandwidths from the 20 m and the 15 m HAM radio bands. Using the recordings feels like having actual receiver hardware under your SDR.

Share Quadrus SDR

DIY SIGINT platform not only for James Bond

Follow Quadrus SDR

Using a SIGINT platform at home? Why not!

If I say signal intelligence (SIGINT), you probably imagine something secret, smart, and serious. In most cases you would right, this signal detection approach is associated with war and secret services – but not all the time. Technological developments can be used for benevolent and nefarious purposes alike, like nuclear fission or SIGINT.


Fly like an eagle… sorry, like a balloon

Some very creative guys at The Frank-Ratchye STUDIO started a project to build and test a low cost SIGINT platform. The Project is called “The Deep Sweep”. The aim was to build a receiver to intercept out-of-reach signals between the ground and the stratosphere. Yes, you would be right in your assumption: these are HAM radios.


Maybe the developers read that part of Winnie the Pooh too many times, when he flew up with a blue balloon to steal the honey from the bees. They did something like this. They stocked together a big, fat weather forecast balloon with a small embedded computer and some RF equipment. And here you go: a DIY SIGINT platform.  And it works!


The signal ranges currently captured are:

LF/HF: 10 kHz – 30 MHz (long range comms in transport, military, marine)
UHF: 650 MHz – 1650 MHz (military, weather, marine)
SHF: 10 GHz – 12 GHz (satellite communications, drones/UAVs

The equipment was tested twice in Europe. They launched the balloon in Germany, and it landed first in Poland, and a second flight ended in Belarus. Unfortunately, the first flight was not so successful due to a battery fault, but the second was unexpectedly long, and prosperous. The developers are planning to continue the tests in Europe and in the USA in the next couple of years.

Sounds nice? Why don’t you DIY?

To get more details on The Deep Sweep Project, visit their site. You can get a list of the employed hardware and software components, and you may download the captured signals. If you take a fancy to do an own SIGINT platform at home, don’t hesitate to share it with us on our FB page, or send us the whole story with pictures, and we will share it in our blog as a guest post!

Do you need something professional to receive all interesting signals on your sky? Learn more about Quadrus SDR platform.

Would you like to have HF signals with the best performance? Get a HF preselector filter – FREE design and layout.


Share Quadrus SDR


Must have books for SDR fans

Follow Quadrus SDR

Stay tuned with SDR, the wireless revolution is just the beginning

Are you up to date in SDR literary? Let us help you with some recommendation of new or not enough well known book of this topic. This is the first part of our new series.

In the middle of September 2015 one of UK’s leading technical campuses University of Strathclyde Glasgow published a pretty good book about SDR device usage.


SDR using MATLAB & Simulink and the RTL-SDR

In this book they introduce readers to SDR methods by viewing and analyzing down converted RF signals in the time and frequency domains, and then provide extensive DSP enabled SDR design exercises which the reader can learn from.

The hands-on SDR design examples begin with simple AM and FM receivers, and move on to the more challenging aspects of PHY layer DSP, where receive filter chains, real-time channelisers, and advanced concepts such as carrier synchronisers, digital PLL designs and QPSK timing and phase synchronisers are implemented.

In the book they will also show how the RTL-SDR can be used with Software Design transmitters to develop complete communication systems, capable of transmitting payloads such as simple text strings, images and audio across the lab desktop.

Quadrus SDR with MATLAB & Simulink

The text book examples are based on the well known RTL SDR hw, however for high performance HF receiver implementation the DRU-244A based Quadrus SDR platform provide better performance.
One of the way how you cam connect the Quadrus SDR to Matlab or LabVIEW or other signal processing software package is using standard windows based .wav files.
We used this method too for proving the performance of synchronized multi-channel receiver capability as you can find it in the following post in the Quadrus SDR Blog:

In the post you can find the download link for the Matlab script for reading the .wav files generated by the SRM-3000 receiver software of the Quadrus SDR platform.

Would you like to buy it now? If you don’t find an available copy on Amazon, try this source.

Share Quadrus SDR


MAP65 Quadrus SDR connection

Follow Quadrus SDR

Setting up MAP65 Quadrus SDR connection with virtual audio cables

In order to implement the MAP65 – Quadrus SDR connection, the output audio stream of the channel should be routed to the installed virtual audio devices in Windows. In case you have virtual audio cables installed, it is possible to select one for each channel as you can see it in the picture below.


The standard, speaker output device is used to monitor the channels in this example. The four channels of the receiver are connected to four different virtual audio cables.
We have to select one other virtual audio cable – like VAC line 5 in our example – in the MAP65 software. Finally, the streaming software can be started to connect the receiver and the decoder software.

inp   stream

MAP65 Quadrus SDR connection testing

We can find a strong signal in the receiver window, and the same signal will appear through the virtual cable in the MAP65 wideband spectrum display too.


Please note that the output sample rate of the SRM SDR receiver is only 48 kHz, but the input sample rate of the MAP65 is 96KHz. The VAC software makes the interpolation between the two different sample rates. Thus, the inner +/- 24 kHz part of the MAP65 display will contain valid spectrum components.  The interpolation is done without any filtering, so we will see the image spectrum beyond the 24 kHz limit. If we set up a 15 kHz filter in the SRM SDR receiver, we can see the noise level in the spectrum accordingly and mirrored to 24 kHz as well.


In the picture above, you can see the signals from the generators which was set +/- 4 kHz around the nominal frequency. As you can see, the signal was positioned beyond and below the center using the IQ streams from the receiver. The same kind of signal tuning can be seen in the screen recording below.



Successful MAP65 – Quadrus SDR connection via virtual audio cables was proven using the IQ demodulator of the SRM SDR software. Virtual audio cables were used during the test, and the streaming software of the VAC package was employed for connection and to implement re-sampling between the different audio sampling rates of the two software.

Share Quadrus SDR

Multi-channel SDR production system

Follow Quadrus SDR

Mult-channel SDR receiver

I’ve already published some posts on the multi-channel decoder capability of the Quadrus SDR fairly recently. However, I ended up doing some new tests with the MULTIPSK decoder, because some questions were raised.
As we’ve described it already, the DRU-244A based Quadrus SDR platform has multi-channel capability. It can be used to deliver up to 16 channels to the decoder system. Thus, it can be used very well in a production environment too.

MULTIPSK decoder software

This software stack was developed and is maintained by Patrick, F6CTE, and can be used to run different digital modes in the RF bands. In the SWL and UDX operation modes, we can use its receiver decoder capability. It contains a lot of HAM radio and professional digital modes, as you can see below.


Some of them are available in the free version, and some of the professional functionality is only available in the licensed version, which has a reasonable price.

Connecting Quadrus multi-channel SDR and MULTIPSK decoders

The easiest and most convenient way to build a multi-channel SDR production system is by using virtual audio cables (VACs) to connect the audio output of the Quadrus multi-channel SDR to the decoder software. In case we’d like to use the full capacity of the receiver, we need some cables and some instance of the decoder running on the computer. To do that I just needed to understand the audio settings of the decoder software. After a short email exchange with Patrick, I understood that the MULTIPSK stores the audio and other settings in config files located in the program folder of the application. So, I just needed to make four different copies of the program in four different folders, and set up the audio input to the different VACs accordingly. I’ve made shortcuts on my desktop too. I assigned the VAC 1..4 to the four channels of my receiver, and I used the same set up with the decoder too.


Testing multi-channel SDR production system

I tuned to the different frequencies – used by meteo stations from Hamburg – as follows: DDK2 4583 kHz, DDH7 7646 kHz, DDK9 10100.8 kHz.,templateId=raw,property=publicationFile.pdf/Schedule_rtty_01.pdf
Then I tuned the fourth channel to the 20 m amateur band. As you can see from the receiver screen, the reception in the late morning time is pretty poor at 4.5 MHz, however, the upper bands have strong signals. At the output screen of the decoder, we can see the meteo messages and the ham radio calls in the 20 m band.




If your decoder software has the capability to run multiple instances at the same time on the same computer, you can integrate a very powerful multi-channel SDR production system. The connections between the receiver and the different decoder software can be implemented as virtual audio cables.

Share Quadrus SDR

Multi-channel SDR decoder

Follow Quadrus SDR

What is a Multi-channel SDR decoder receiver?

As I’ve described in my earlier posts, the DRU-244A SDR digitizer hardware contains up 16 radio channels as hardware Digital Down Converters (DDCs). These can be distributed in 4 channel blocks between different antenna inputs. One signal processor contains 4 channels and supports one input, which presents a limitation when pairing antenna inputs and receiver channels.

Integrating the multi-channel SDR receiver with external decoder software

There are several ways to integrate the DRU-244A based Quadrus SDR platform with external software packages.

  • direct programming of the DRU-244A SDR hardware employing its API
  • programming the SRM-3000 SDR software using its API
  • and simple audio connection with virtual audio cables

All the API descriptions can be found in the documentations of the muti-channel SDR hardware and SDR software. They can be downloaded from the support page on the Quadrus SDR site:
The first two methods requires some programming, however, the third one does not. It is very similar to connecting  your old hardware receiver to a decoder software. But in this case, the receiver itself is a software too. So, we just need a virtual audio cable.

Setting up the audio outputs

In the options menu you can assign an audio out device for all of the SDR receiver channels. Also, you can select the monitor sound device as well.

audio settings2

If you start each channel, the sound output of the demodulator will be routed to the selected audio device. It will be a mono channel in case of CW/AM/FM/USB/LSB demodulation, and stereo in case of IQ demodulation.
The monitor channel is usually employed to monitor the given channel, and has the audio routed to the loud speakers or head phones connected to your machine. If you touch one of the controls of a given channel or press the Monitor button, the channel will be automatically monitored, and you will hear its demodulator output.

Testing multi-channel SDR decoders

After setting up the system with different virtual audio cables, I’ve tested it with some well-known digital decoders, like MultiPSK, MMVari, Digipan. All of the multi-channel SDR decoders worked fine without any problem. Even several copies can be run on different channels and operating modes depending on the available computer resources.

mpsk01 mmvari02 psk31a


It is possible to connect the audio output of each channel of the multi-channel SDR decoder to an external software with virtual audio cables. It was proven to work with several digital post-pocessors, like MultiPSK, MMVari, and Digipan.

Share Quadrus SDR