SDR Radio equipment – It is time for a cool Christmas gift

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A smart Xmas gift? SDR radio Equipment!

Jingle waves, jingle waves, jingle all the way, oh what fun it is to not get socks this Holiday! Your children get the cutest vampire barbies, the latest Star Wars figures, and all the flying, beeping gadgets they asked for. Your wife is happy with her new shinny earrings because her friends and colleagues will be green with envy after Christmas. But what about you? Socks and ties again? No!

This Xmas should be different! Play safe and shop smart. Forget the huge watches and drones. You need something cool. What about an SDR Radio Equipment?

Top 3 ideas if you are interested in Ham Radio:

Beginner level – It is a beginning of a beautiful friendship with the waves. Check and buy Get on the Air with Hf digital Guide to know all what you need for becoming a Ham Radio.


Advanced level – Somebody dreaming of white Christmas. Who cares about snow? All you need is a really good HF antenna, get it here.


Black belt Ham Radio fan level - Would you like to develop your Ham Radio station? Why don’t you enter the 21th century with an SDR platform like Quadrus SDR!


Have you ever heard about Black Friday? It is the day when the Christmas Shopping Season (your wife’s/girlfriends kind of madness) begins in the USA. In the last couple years, this day became known globally, so these days most everyone can make good bargains in November.

Our special offer Quadrus SDR Christmas Pack is available this Christmas only, from November 25th to December 14th.

The offer includes:

  • A DRU-244A card, which can be found in our webshop
  • 3 hours of VIP customer support from one of our seniors consultants – only available in this offer
  • Free shipping to anywhere on the globe

Hurry up, because the stock is limited, and if you order until December 6th, you are also getting a bonus:


So, do you want the socks again? Or something really smart?


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How to receive NOAA satellite signals

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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 http://celestrak.com/NORAD/elements/

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: http://www.wxtoimg.com/downloads/


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:


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Must have SDR books – part 2

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Going digital? An essential SDR book to start

This week I heard that the average age is around 60-70 years on Ham radio events. Isn’t it funny? Well, in most cases Ham radio is something grandpa does in his garage, but I hope that will change. Why? Because Ham radio is a smart hobby, and you have to be smart to make it work. Especially in the digital age with Software-Defined Radios (SDR) like QuadrusSDR. That is the real challenge, not the shinny, beeping gadgets that can not survive a day without charging, and are absolutely deadwood without internet connection. If you don’t have a grandpa at home with Ham radio knowledge, or you are a grandpa who would like to go digital, you should have the following books in your SDR book library.

Get on the air with HF digital

This book is published by the American Radio Relay League (ARRL), which is the national association for amateur radio enthusiasts in the US. Today, with more than 161,000 members, ARRL is the largest organization of radio amateurs in the world. The author – Steve Ford WB8IMY – gives clear, often step-by-step instructions on how to go about setting up an HF digital station – everything from attaching cables to configuring software. Even though software changes over time, the instructions provided in this book are likely to apply across several software versions.


The text includes instructions for configuring software programs for popular modes such as RTTY, PSK31, and JT65. You’ll also learn about other digital communication modes such as MFSK, Olivia, and PACTOR. We have already posted on some of these in connection with QuadrusSDR:

Get On the Air With HF Digital emphasizes the hands-on approach. The goal is to give you all the advice you need to take to the airwaves as quickly and easily as possible.

If you feel the superpower to develop your SDR knowledge check the next step book in this post.

While waiting for Amazon to deliver your book, read my previous post where you can find some additional info and nice pictures of my first Ham radio equipment (from my age of 17).

And if you feel stuck mastering in the ways of the Ham radio, ask us on our FB page or below this post, and we will try to help you progress.

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Direct digital receiver – when HAM radio can save your life

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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.


Source: cnn.com

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!

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SRM GUI tips and tricks series – RF record and playback

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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: http://spectrafold.com/quadrus/support/

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.

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Have your own HAM SWL radio station!

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Gadget of the past? HAM SWL radio station!

In most cases we write posts about unique designs and ides, which are useful for advanced level HAM SWL radios, e.g., this or that posts on software defined radio (SDR) technology. But what about the beginners? Well this post is for them! Ready, steady, HAM SWL Radio!

Some weeks ago I was surfing the internet looking for some new ideas for a special issue of Quadrus SDR. It was easy to find a creative idea for my problem, and to prove to my family that HF broadcasting is alive. We can access high quality radio service there based on new, digital operation mode (i.e., DRM), which has a very useful community for SDR fans. When I started to deal with HAM SWL radio, there were no opportunities such as the internet. It was ooch… 35+ years ago. We – the members of the community – talked to each other only using the radio at the club station or using our self-made radios at home, but it was an amazing experience that I never forget. I had my own HAM radio station at home – built with my own hands from scratch – with CW capability for the 80m ham radio band. Lovely, isn’t it? (and I was 17 years old when I made this…)

front internal top front

I have two sons. They are not interested in making, but they are professional in using gadgets. Like every teenager nowadays. Maybe my father said the same thing about my HAM radio equipment. Gadget.

Do or do not, there is no try

So, what about beginners? I found a very good post about how to start this kind of a hobby. Hobby? No! This is a way of life. I could not summarize this better then Gregory L. Charvat:

“The only way to get started is to build something. Start small, check out the QRP community, try making a single-conversion receiver, and move up to something with a crystal IF filter. Borrow and scale circuits from books such as these:

Or leverage complete ICs and modules like those from Mini-Circuits.  There is nothing like making that first long distance contact (DX) on radio gear you created from scratch.”

You can read the whole article on Hackaday.

But if you are more of a computer geek, you can switch to software implemented radio and start with less complex and less expensive SDRs or a professional one like Quadrus SDR from our webshop. Even I experienced that old fashioned radio moment Gregory mentioned above, when I first received a DRM station from Mubay, which was a very nice feeling for my radio infected heart. You can see the report on this reception here in the Quadrus SDR blog:

Further reading on DRM, the new digital HF broadcast technology:

And don’t forget to share your success stories or questions regarding SDR issues with us on our Facebook pageTwitter page, or G+ community page. Be social; whatever is your preferred platform, we are there !

Bertalan, HA6QU

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DIY SIGINT platform not only for James Bond

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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.


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Hunting for FM repeater frequency?

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Ways to easily find FM repeater frequencies

Version 1 – The USA is not that far away

The lowest FM repeater band for ham radio can be found in HF between 29.6 and 29.7 MHz with channels 10 kHz apart and with a frequency shift of 100 kHz.
The advantage of this exciting HF band is it’s long distance communication capability when propagation conditions are at least fair, i.e. Solar Flux Index (SFI) is high enough, and the geomagnetic Kp index converges to zero – or at least not greater than two.
HF frequency propagation is tricky, and solar flares may produce X-rays as well, but the ten meter band is not so vulnerable, which is why it was chosen for repeaters.
In practice I have often heard 29 MHz repeaters from the USA.

Version 2 – World wide waves

Another widely used band is allocated around 145 MHz with 12.5 kHz channel spacing and a 600 kHz frequency shift. There are a great number of FM repeaters all over the world employing it.

A detailed list can be found here:

Somewhere on the high mountains

Some popular repeaters are sited on high mountains, and can cover a rather large geographical area. An example is the Királyhegy (Králova Hola) repeater near Poprad, Slovakia transmitting (downlink) on 145750 kHz. It’s a bit old styled, because one must use a short 1750 Hz tone burst to start communication. Beside this, you can use it without CTCSS code. A transmission from this repeater can be seen on the waterfall display of the SRM-3000 software receiver running on the Quadrus SDR platform in direct digital VHF mode.

Screen Shot 01-02-15 at 08.09 PM

According to a recent International Amateur Radio Union (IARU) recommendation, 145 and 432 MHz FM repeaters are mostly equipped with CTCSS encoding. Without that code one can not communicate through these repeaters.

Learn more about CTCSS encoding.

One can see the locations and callsigns of repeaters in Google Earth using the file waypoints.kmz.

This is an example from the Carpathian Basin:


Callsign dictionary

Those callsigns with a letter V in the suffix are 145 MHz FM repeaters, and those with letter U in them are UHF repeaters. UHF repeaters have been more popular recently, which is partly due to the small sized antennas used mainly with hand held radio sets. Channel spacing is usually 25 kHz, and the frequency shift is 7.6 MHz in the 435 MHz FM repeater band.
CTCSS codes are generally used on almost all 70 cm repeaters.
The perhaps best Hungarian UHF FM repeater, HG7RUE, is sited on Szechenyi Hill in Budapest in the old building of the first TV broadcast transmitter. Its downlink frequency is 438775 kHz and the CTCSS code is 114.8 Hz. As the DRU-244A SDR digitizer hardware in the Quadrus SDR platform has no input frequency limitation, one can use the receiver in direct digital mode even up to the 70cm HAM radio band.

An interesting link of the Hungarian repeater map:

Special thanks for the info and content to HA6NN, Bandi.

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Must have books for SDR fans

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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.

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HF preselector filter

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Direct digital HF receiver

Earlier we’ve introduced the concept of direct digital receivers in this blog.


Furthermore, VHF/UHF direct digital filters discussed:



In this operation mode the ADC input has to be kept clean from various spectrum components in other Nyquist bands. The input preselector filter helps in selecting the right part of the given Nyquist band.

The HF preselector filter

In case of high performance reception of HF signals, the main challenge is to prevent interference from higher frequency VHF/UHF signals. This may be achieved with a Low-Pass Filter (LPF) cutting the components above say 30-32 MHz, but that depends on the reception requirements. We have to carefully construct the filter such that it provides sufficient attenuation in the 88-108 MHz FM band, where the highest level signals may be found usually. The input bandwidth of the DRU-244A hardware is up to 440 MHz, thus the input filter should attenuation in the upper VHF/UHF band as well. This can be ensured with careful design and implementation using small, surface-mounted components. If we are concentrating on real HF signals, and are not interested in lower band mid- or long-wave reception, the input should be clean from high level AM broadcast signals as well, usually present in the spectrum below 1.6 MHz. For this purpose, a High-Pass Filter (HPF) should be inserted in the signal path with a 1.6 MHz corner frequency.

HF preselector filter design and realization

To satisfy the requirements of the HF input preselector filter described above, we’ve designed an input filter block with a cascaded HPF and LPF using a professional filter design software. The approximation is elliptic, ensuring a cutoff at 40 MHz. The implementation is a small PCB containing the HPF and LPF sections with SMA connectors at the ends and a place for an optional choke for remote powering capabilities of an active receiver antenna.

The photo of the finished HF preselector filters:
The measurement results up to 500MHz:


The full design package of the HF preselector filter, including the schematic and layout design in Protel (Altium Designer) file format, are available for download.

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