Tagged: sdr radio


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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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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Quadrus SDR for DRM receiver in education

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AM and DRM broadcasts in the HF bands

Traditionally, AM modulation is used in the LW/MW/SW bands for broadcasting purposes. It is very easy to identify these the AM broadcast stations based on their Dual Side Band (DSB) shape in the spectrum. The spectrum and waterfall displays of the Quadrus SDR show such a modulation on the following pictures.

am spectr
am water

However, digital waveforms, i.e., DRM, have started to populate the HF bands, which can provide high quality content. The modulation format is optimized to the propagation behavior, and is based on the multi-carrier scheme. It is also very easy to recognize them in the band using the Quadrus SDR for DRM, because these stations have a distinct rectangular shape in the spectrum.


DRM in the telecommunication curriculum of universities

As DRM represents a significant part of broadcasting systems nowadays, most universities around the world have included this standard, or parts of it, into their curriculum on telecommunications. It is also an important part of the telecommunications program at the Budapest University of Technology and Economics as well, where we have recently introduced the Quadrus SDR for DRM by showcasing its DRM reception capability.

DSC_0478 DSC_0523

drm05 drm02



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Low-frequency reception with Quadrus

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What is low-frequency reception?

Well, it depends on your primary activity area. For regular High Frequency (HF) guys the lower end of the HF band is around 1.8 MHz or 160 m wavelength. Below the HF or ShortWave (SW) band we can find the Medium Wave (MW), the LongWave (LW), or even the very longwave bands too. These are usually called Low Freqeuncy (LF), Very Low Freqeuncy (VLF), Extra Low Frequency (ELF).  Additional information can be found here: http://en.wikipedia.org/wiki/Frequency_allocation

Low-frequency reception limit of Quadrus SDR

The DRU-244A SDR digitizer hardware of the Quadrus SDR platform has AC coupled inputs. Thus LF reception on the platform is limited by the transformer at the input stage. According to the datasheet, the lower frequency -3 dB band edge is at 60 kHz.

Practical tests

I’ve used a simple inverted-V shaped 2×20 m G5RV antenna and bypassed the usual High-Pass Filter (HPF) in the HF receivers.

First, I looked at lower frequencies than MW broadcast bands, and I’ve found some interesting signals in the 300-400 kHz band.

mw01 mw02
mw03 mw04

There are a couple of Double SideBand (DSB) AM transmitters with strong carriers modulated by simple Morse code. These can be heard with a simple AM receiver as well. It is very simple to copy them, and you can visually decode the call sign from the waterfall diagram. Later, I’ve learned on one of the forums that these are Non-Directional Beacons NDBs for navigation proposes. More info here: https://en.wikipedia.org/wiki/Non-directional_beacon

Low-frequency reception of LW broadcasts

The lower part of the band, around 150-250 kHz, contains again AM modulated LW broadcast stations.

mw05 mw06 mw07 mw08

Low-frequency reception the DFC77 transmitter

Below 100 kHz we’ve found some interesting signals. I was only familiar with the DCF77.

mw09 mw10

This is a time-frequency standard from Hamburg. http://en.wikipedia.org/wiki/DCF77 It can be received very well with the wire antenna, and decoding the message is also possible with a special decoder program SpectrumLab by Wolf, DL4YHF.



The LF reception capability of the Quadrus SDR platform was introduced. NDBs were received in the 300-400 kHz band. The LW AM broadcast stations in the 150-250 kHz band as well. The well known DCF77 reference transmitter was received and decoded at 77 kHz and some signals were detected around 50 kHz. LF reception needs some modification on the analog input stage of the receiver hardware.


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r1anr_28mhz_1501151040ut1-830x945 - feature

WSPR Quadrus SDR

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WSPR Quadrus SDR

What is WSPRNet?

In my last post I’ve introduced the WSJT receiver software and mentioned WSPRnet.
Weak Signal Propagation Reporter Network is a group of amateur radio operators using K1JT’s MEPT_JT digital mode to probe radio frequency propagation conditions using very low power (QRP/QRPp) transmissions.

WSPR Quadrus SDR on WSPRNet

Registered user can log in to the site, and their client software will send automatic updates on the currently received radio stations to the database. The connections are visualized on a map. Again, thanks to Andy, HA6NN, we have some pictures about the stations he was receiving with the WSPR Quadrus SDR.

Connecting WSPR Quadrus SDR

I’ve used the virtual audio cable connection in this experiment as well in order to send audio samples from the SRM-3000 SDR software of the Quadrus SDR platform to the WSJT software.


In this post, you see an example of using Quadrus SDR with external software connected through a virtual audio cable. The setup received some DX stations with the DRU-244A SDR hardware, which has enough sensitivity to receive signals from around the word with a simple wire dipole antenna.

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WSJT Quadrus SDR

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WSJT Quadrus SDR

What is WSJT?

WSJT is a special waveform developed for weak signal communication by Joe Taylor, K1JT. It can be used in Earth-Moon-Earth (EME), meteor scatter, and ionospheric scatter scenarios at VHF/UHF; but skywave propagation is supported as well in the HF band. The waveform can fit in the 3 kHz bandwidth, so SSB transceivers can be used.

How to use WSJT with Quadrus SDR?

The easiest way to integrate Quadrus SDR with external signal processing software is by employing a virtual audio cable, which passes audio samples from the SDR directly to the external software. See this post for further details:


DX SWLing with WSJT Quadrus SDR station

Andy, HA6NN has kindly set up a station for a day during the 2014/15 holiday season, and has collected some good data using WSJT and the Quadrus SDR. The image gallery shows signals received from AC2PB, BA4TB, BD8XY, CO2VE, DC6CM, DL7ACA, EA3KY, HS0ZBS, JH1AWZ, K1NOX, K6ESU, LW3DJC, LY2CK, N1NU, N6DM, OH1LWZ, RK6ART, RN1BL, S5500, TF2MSN, UA9CC, VK5DG, XE2FGC, and ZP5yV.

Visualization with WSPRnet

There is a community site, where you can visualize your connections and received stations. Andy has generated some good screenshots using his WSJT Quadrus SDR receiver.


I know he is looking for a contact with R1ANR. I hope he has it on his DXCC list soon…


In this post we’ve described how to connect the WSJT wavefrom with the Quadrus SDR using a virtual audio connection in order to receive weak signals. The WSJT Quadrus SDR combo was able to detect a lot of different DX stations, and proved the reception capability of the DRU-244A SDR hardware.

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SDR pre-selector filter | Direct digital SDR

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What is direct digital SDR?

Software-Defined Radio (SDR) is a type of radio, where the analog signal is converted into the digital domain, and functionality is implemented in the digital domain employing signal processing algorithms. Conversion technology is limited in terms of bandwidth and frequency range, thus the right point for conversion has to be carefully chosen. Conversion can take place at the baseband, Intermediate Frequency (IF), or directly at the Radio Frequency (RF). In case conversion happens at the operating RF (likely after the pre-selector), we can talk about direct digital SDR.

Domain converter frequency parameters

Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs) are employed to bridge the analog and digital domains on the radio hardware platform. Converter parameters determine how we can use them in the radio implementations.

Instantaneous bandwidth

One of the most important parameters is the real-time bandwidth or instantaneous bandwidth. It is determined by the sampling frequency of the converter, and according to the Nyquist law, it is equal to the half of the sampling frequency.

Frequency range

The other very important parameter is bandwidth or frequency range of the converter itself. Usually, this is determined by the circuits involved: it starts with the analog components, and includes circuitry within the converter, like the sample-and-hold stage. The Nyquist criteria states that the bandwidth should be equal to the half of the sampling rate in order for a perfect reconstruction in both time and frequency domains. Hence, there is a possibility to generate and sample higher frequency signals too, if we keep the bandwidth inside half of the sampling rate. In other words, we can use upper half bands, called Nyquist bands. If we have a wider spectrum, we have to be sure not to alias or fold from higher Nyquist bands to the baseband. The anti-aliasing filter or SDR pre-selector is used for that propose. If we are talking about ADCs and receivers, the latter terminology is employed.

Frequency parameters of the DRU-244A SDR hardware

We’ve used 80 MHz as sampling frequency for our hardware platform, so, the instantaneous bandwidth is 40 MHz. We can tune to radio channels within this band using on-board hardware DDCs. The input bandwidth of the ADC itself is 650 MHz. This is the -3 dB point of the input stage, and it has no brick wall slope.

bandwidth response

This means that we can use not only the 0-40 MHz first Nyquist band, but upper bands, like 160-180 MHz, too using an SDR per-selector filter. However, the bandwidth is degraded, because we have to use some other input analog circuits, like input low-noise preamplifiers and leveling attenuators. Still, it is possible to receive with good results up to 500 MHz. See this post about satellite signal reception at 435 MHz:
For more information, please see AN-835 application note from Analog Devices:

Designing SDR pre-selector filter

You can find a lot of different filter design tool kits on the net, which will approximate your requirements, and determine the right components for different realizations. I think, the best practice, – which I’ve used in the last decades – is to cascade a separate high-pass and  a low-pass filter if the relative bandwidth is high. On the other hand, the band-pass approach will work for narrow band (<10%) filters. I always like to use standard components. E12 or E24 1% components will do good job for anti-aliasing and pre-selection filter implementations. Usually, the capacitors are the easier part, inductors may have to be manually wound and tuned.

Bandpass filter for VHF bands

Using the Dyonusos filter design software, I’ve designed a band-pass SDR pre-selector filters utilizing the capacitive coupled resonator structure, which is my favorite. The relative bandwidth is higher than 10%. During the approximation phase, I like to see ~40 dB attenuation at the Nyquist band corner. However, only 30 dB could be achieved by the high-pass filter at the lower band edge frequency if the insertion bandwidth was kept at 20 MHz. You can see the calculated filter response, the filter values, and the measured response after having very careful fine tuned the inductors in the circuits. Seems easy enough, but you need some practice to reach such results with a 5th order resonator filter. For beginners interested in designing and implementing filters, let me suggest to start with 3rd order structures and standard complements as close as possible to the calculated component values.


SDR pre-selector BPF 160-200 SDR pre-selector BPF 120-160


SDR pre-selector BPF 120-160 SDR pre-selector BPF 160-200


SDR pre-selector BPF 160-200 SDR pre-selector BPF 160-200


SDR pre-selector BPF 160-200 SDR pre-selector BPF 120-160

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CW Skimmer – Quadrus SDR

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What is a CW Skimmer?

A CW Skimmer is multi-channel CW decoder and analyzer by Alex, VE3NEA. You can read about this great tool and his other works on his website: http://www.dxatlas.com/CwSkimmer/

A great tutorial is available from Pete, N4ZR as well: http://www.dxatlas.com/CwSkimmer/Files/Skimmerintro.pdf

Go ahead, and look at the links if you are not familiar with the topic.

How to connect the CW Skimmer and the Quadrus SDR ?

The CW Skimmer is accepting signals from radio receivers. The traditional hardware radio can be connected through a sound card audio input to the software, and the CW Skimmer software can remote control the receiver on CAT. The bandwidth, in this case, is limited to the usual 3 kHz of typical HF radios.

However, the CW Skimmer software can handle a couple of SDRs too, and can accept higher bandwidth signals from them. Some of the SDRs on the market can also be controlled from software trough their APIs.

Today the CW Skimmer – Quadrus SDR connection is not supported directly by the CW Skimmer. Thus, we have to use the simple audio interface connection. This limits the analysis bandwidth to 3 kHz. Because the SRM-3000 SDR receiver is software too, we can use a virtual audio cable to connect to the CW Skimmer. I’ve used the VB-Cable A&B from VB-Audio Software for my tests. A single connection is free for non-commercial use.

Decoding calls in the 20 m band

Yesterday, I had a chance to use one of the remote stations with TeamViewer. It is located in the country side with a simple inverted-V shaped G5RV wire antenna. I found a spot around 14.025 MHz in the CW band. There were a lot of stations in the 3 kHz bandwidth. The outcome of only a couple of minutes of recording can be seen below with the call signs collected by the CW Skimmer.


Further improvements with server version CW Skimmer

There is another software from Alex called CW Skimmer Server. This application can handle up to 192 kHz bandwidth in seven ham radio bands. The SDRs can be connected with a 3rd party driver. We are looking for interested programmers to provide a driver to CW Skimmer Server based on the TCP/IP remote control interface of the SRM-3000 SDR software receiver.

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Using Quadrus SDR with a laptop

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Why a laptop?

Even until fairly recently, the resources offered by an average laptop were insufficient to run wide-band, multi-channel SDR applications. Thus, the original SDR hardware was designed with more capable desktop computers in mind. However, with increasing laptop performances, it is now finally possible to run even the more challenging applications. The obvious advantages are flexibility and mobility, and by now they are omnipresent in our everyday lives.

Connecting Quadrus SDR to a laptop

The Quadrus SDR platform’s phase-coherent SDR hardware digitizer board is a standard PCI slot card. This form factor does not allow us to connect it directly to a laptop. Fortunately, we have the possibility to use an external PCI slot extender, and place the DRU-244A card into one of the external slots. There are several products in the market, they differ mainly in the number of slots and connections. One of the most well known suppliers is Magma, who offers different solutions, like the one slot PCI extension. They also offer products with different interfaces to the laptop: ExpressCard 34mm and 54mm versions, and CardBus/PCMCIA card with 1 m or 1.5 m cable length.

1slotB_xl_0 1SlotPCI_connection

Beyond this well known and proven supplier, we’ve just found another very cost-effective external PCI solution. Polotek offers a solution based on the ExpressCard interface. It essentially contains one PCIe and one USB interface. Their idea is very simple: use the PCIe connection with a high-speed extender cable and add a PCIe-PCI brige chip on the external slot card. Their other approach is to use a standard USB3 cable manufactured in high volume. However, the connection itself is not following the USB3 protocol, they simply utilize the high-speed differential wire pair within the cable to connect the PCIe slot to the extender card, which has the PCIe-PCI bridge.

polotek2 polotek

Testing the DRU-244A phase-cohernet SDR hardware digitizer with a laptop

You can place low volume orders at several places:
I’ve ordered from Aliexpress, and received the package with the components as shown on the web.

dru ext1 dru ext2

Setting up the hardware and installing the DRU driver was trivial. The single issue, I’ve noticed, is that the Plug-and-Play functionality is somehow not working properly in all cases. Sometimes I’ve lost connection to the card after some sleep or screen saving actions. In these cases, I just removed and reconnected the ExpressCard and re-initiated the Plug-and-Play cycle. I had no chance to test it with any other computer than my Dell power notebook with an i7 processor.

dru driver machine

driver1 driver2 driver3



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SDR hardware manufacturing batch arrived

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Design and preparation of manufacturing

The DRU-244A digitizer SDR hardware went trough some design polishing and preparation for mass production without close interaction with the original design team.


Verification and testing

Before releasing the SDR hardware, the manufacturing plant is responsible for the full verification and testing of all functionality. They need to program the clock chip that provides the different sampling clocks and other miscellaneous clocks of the architecture as well. After that, the initial EEPROM content of the PCI interface should be loaded. If the card is working fine with external power supply at this point, it can be placed into a PC for further testing using its test software. In this phase, the RF parameters are tested.

dru-sample-app dru-sample-fequ

Beta testing with selected users

After all the cards were tested in the factory, we’ve immediately shipped some of them to our beta testers. They have the latest version of the SRM-3000 receiver SDR software available to use with the card. We are looking for the initial responses from them, and appreciate any suggestions for further improvements.


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