Tagged: sdr radio software


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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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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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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BD8XY_IF_Rec_150113114300-830x990 - feature

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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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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Sensitive SDR receiver

Sensitive SDR receiver for sensitive information

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[Sensitive SDR receiver for sensitive information]

Sensitive SDR receiver based on the DRU-244A digitizer SDR hardware platform

The DRU-244A digitizer board was designed and implemented for building radio receivers. It contains a 16 bit resolution low-noise Analog-to-Digital Converter (ADC). It has a low-noise input preamplifier and an input attenuator in front of the ADC. The low-noise preamp provides input sensitivity as low as -111 dBm in SSB reception mode with 2.1 kHz bandwidth and 10 dB SNR. With external preamplifier it could be as low as -122 dB. If you would like to see more detailed test results on SDR receiver sensitivity click here:

Practical results for receiving weak signals

I’ve already made some practical tests with my very simple inverted-V shaped wire dipole antenna. It was used in the country side, so there was less human made noise than in the crowded city or urban area.

Sensitive SDR receiver as long range DRM SDR

If you are not a professional radio enthusiast with a vast knowledge of exact broadcasting carrier frequencies, one of the easiest ways to find some DRM radio stations is to just look for its unique spectrum in the HF band. The DRM spectrum is a very typical, noise like, wide band signal. This is exactly what I did; I simply connected the antenna to my receiver through a 30 MHz low-pass input pre-selection filter, and started visually looking for DRM radio signals in the spectrum. I was really surprised when one of the first signal received turned out to be be coming from India and the next one was from South Africa. Not bad. The SDR receiver seems to be real sensitive if I am able to decode these signals in the middle of Europe.

drm01 drm02

If you are interested in how the SDR receiver was connected to the Dream DRM decoder software, please read these posts:



Sensitive SDR receiver for secret transmissions

One of my other favorite signals in the HF spectrum is the UVB-76 Buzzer on 4555KHz.




As the frequency is well known, I could simply dial it in to the SDR receiver software, and immediately see the transmission on my screen and hear the famous “Buzzer” tone on the speaker with very high Signal-to-Noise Ratio (SNR).

Receiving the UVB-76 Buzzer on 4625KHz with sensitive SDR receiver

There are a lot of mysterious signals in the HF spectrum. The sensitivity of our receiver – especially with an external, low-noise per-amplifier and a good antenna – makes it possible to listen to even the most remote signals.

listener Contact014

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