After a short break Frugal Radio's ongoing series of SDR beginners guide videos is back, and in the latest episode Rob provides part one of a two part overview of some software available to use with software defined radios such as the RTL-SDR.
In the video he demonstrates general Windows based receiver programs like SDR#, SDRUno, SDR-Console V3, HDSDR, as well as multiplatform software such as SDR Angel, GQRX and CubicSDR. He finishes up by explaining the options available for virtual audio cable programs, which are required to pipe audio from general receiver programs to decoders.
A few days ago we posted about Hayati and others' work in creating a new release of the librtlsdr drivers which implemented some new interesting features. However, at the time of the post there was no GUI for actually making use of the features easily. Now Hayati has released a new rtl_tcp ExtIO interface.
The interface exposes the ability to manually adjust the filtering within the R820T tuner. This is quite useful for managing out of band interference and raising overall dynamic range especially when trying to listen to a narrowband signal. It also exposes decimation controls, tcp connection features like auto reconnect and persistent connection, manual IF gain control, the ability to choose USB vs LSB tuning, and the ability to choose the highest stable sample rate of 2.56 MSPS.
The ExtIO interface is only available for SDR programs that support ExtIO, such as HDSDR. To test the ExtIO, first download and extract the latest librtlsdr release then run rtl_tcp from the command line. Extract and run the new ExtIO dll into the HDSDR folder, then run HDSDR, making sure to select the new dll when it asks on startup. You can then set the desired bandwidth and the matching decimation settings for that bandwidth.
Over on our forums Andy (M0CYP) has posted about his new meteor scatter detection program which works with HDSDR and any supported SDR like an RTL-SDR. It works in an interesting way, as instead of analyzing sound files for blips of meteor scatter activity it analyzes screenshots of the HDSDR waterfall. The software automatically grabs the screenshots and determines if a signal is present on any given frequency. You can set a preconfigured detection frequency for a far away transmitter, and if the waterfall shows a reflection it will record that as a meteor.
Meteor scatter works by receiving a distant but powerful transmitter via reflections off the trails of ionized air that meteors leave behind when they enter the atmosphere. Normally the transmitter would be too far away to receive, but if its able to bounce off the ionized trail in the sky it can reach far over the horizon to your receiver. Typically powerful broadcast FM radio stations, analog TV, and radar signals at around 140 MHz are used. Some amateur radio enthusiasts also use this phenomena as a long range VHF communications tool with their own transmitted signals. See the website www.livemeteors.com for a livestream of a permanently set up RTL-SDR meteor detector (although that site does not use Andy’s software).
Andy writes that his meteor scatter detection software is still in beta so there might be some bugs. You can write feedback on the forum post, in the comments here, or contact Andy directly via the link on his website.
The popular HDSDR software has recently been updated to version 2.76. After a three year hiatus the HDSDR developers are back in action starting with the 2.75 update which was released in early January. The 2.76 stable version released February 02, 2017 is a minor update with several bugfixes and a few new features. The 2.76 changelog is posted below:
Version 2.76 (February 02, 2017)
– switchable display mode: S-units / dBm – switchable mode for S-meter: RMS / Peak – enhanced accuracy of level indicators. New calibration required! – periodic and explicit level logging into .CSV file – switching AGC to off, sets manual gain value – oversteering/clipping audio does now reduce gain value – not volume – fixed OmniRig handling: “MuteOnTX” – deactivate AFC after frequency/mode changes for a small duration – Fast WAV file demodulation & recording – some new keyboard shortcuts – some other small improvements and fixes
RTL-SDR experimenter Hayati Ayguen (hayguen on GitHub) has released a version of rtl_tcp and an ExtIO module that allows access to normally hidden tuner settings. The ExtIO allows you to manually set the tuner bandwidth of the R820T/2 chip. It can be set almost anywhere between 350 kHz and 8000 kHz. In the standard drivers the tuner bandwidth is normally set at a size appropriate for the sample rate, but in this driver using a smaller bandwidth allows you to filter out unwanted signals whilst taking advantage of the decimation a higher sample rate gives you.
In addition to the tuner bandwidth settings, the ExtIO module also implements decimation controls. This allows you to reduce the displayed bandwidth without sacrificing the sample rate. At the same time the R820T/2 tuner bandwidth is reduced to the visible sample rate, improving filtering.
Hayati writes in the Readme file:
Tuner bandwidth is supported with E4000 and R820T tuners. Changing bandwidth with R820T looks good and shows immediate differences in spectrum. E4000 is not so nice, i can’t see any difference, for the bandwidths below 3400 kHz. I also put in the wider bandwidths, even wider than the samplerate, which will produce aliasing! These might be interesting for wide amplitude modulated signals, e.g. ADS-B.
Decimation of Samplerate is an option for very old and slow computers: Before decimation, a very simple and fast low-quality filter (sum) is applied: y(k) = sum over x( k * (1..decimation) ) ; x() = input samples from rtl_tcp ; y() = output samples to SDR app (HDSDR) The sum produces values requiring more than 8 bit. In addition to this soft-filter, minimize the tuner-bandwidth! You will still receive aliases!!!, but a bit damped compared to directly sampling at the slower speed. The reception’s center frequency (LO) is the most alias-free region.
We tested out the tuner bandwidth functions and it appears to work well. For instance in the following image there is a strong pager signal near 157.9 MHz. At first the RTL-SDR is overloaded by the strong signal causing multiple images to appear on the spectrum. But after reducing the tuner bandwidth to 350 kHz the left side of the spectrum is attenuated, and the interfering pager signal is no longer too strong.
The modified rtl_tcp software (and rtl_(adsb|fm|power|tcp)) also support access to the software activated bias tee on our V3 dongles via the -T flag.
Hayati has also uploaded some slides which show some of the effects of using various different tuner bandwidths.
The beta 2.75 version of HDSDR was released about two months ago. Now the stable version has just been released. HDSDR is a free general purpose SDR receiver, similar in nature to other programs like SDR# and SDR-Console. HDSDR can be downloaded from hdsdr.de.
The author of HDSDR emailed us with the following release information:
this morning we released the final version 2.75. Here’s the changelog:
Version 2.75 (January 01, 2017) – more recording options – support for 8bit sampling format – ideal for RTLSDR, halving RF recording size – display level / clipping for RF and AF – additive noise generator for hiding aliases – Highpass Filter for AM/FM deactivatable – useful for slow digimodes – configurable gain for I/Q output – useful for digimode decoding weak signals of SDRs with >16 Bit dynamic range – Uniform “Calibration” dialog for Frequency/S-Meter/DC Removal/Channel Skew – “Custom color palette” to customize colors of Waterfall/Spectrum and some more – output soundcard no longer necessary (e.g. for recording or monitoring) – support for 8k display resolution (7680×4320) – some new keyboard shortcuts (see ) – extended ExtIO capabilities – experimental transmit capability through ExtIO API interface – many fixes and improvements
Some of the new features were introduced especially for the RTLSDR Dongles:
Especially for decoding this kind of signals (AM/FM) , deactivating the Highpass filter (Ctrl-H) will make the demodulated Audio clearer: long periods of positive or negative levels will not fade towards zero. Find attached recordings and screenshots with active and deactivated highpass filter of a garage door opener demodulated in AM.
– additive noise generator (Ctrl-N) is for hiding some alias carriers in scenarios where the ADC does not see real noise from the antenna. The noise generators level has to be configured carefully for not hiding real signals. A level between -25 to -10 looked fine for me. But that should be measured in a lab.
Below are the mentioned attached images and .wav files.
A new beta version of HDSDR has recently been released. HDSDR hasn’t been updated since 2013, so it is good to see that the author is back in action. HDSDR is a free general purpose SDR receiver, similar in nature to other programs like SDR# and SDR-Console. It was one of the first programs to work with the RTL-SDR dongle and despite a lack of recent updates is still a very solid piece of software.
The new HDSDR is version 2.75 Beta1 and the changes include:
more recording options
support for 8bit sampling format
HDSDR runs without output soundcard
support for 8k display resolution (7680×4320)
extended ExtIO capabilities
many fixes and improvements
The main visual difference we’ve noticed so far is the addition of a text dBM meter under the S-Units meter. We also discovered some new color palettes.
Over on YouTube Jon from SDRplay has uploaded a video showing how he’s used the knobs and interface from a 75 year old Marconi CR100 analogue radio to completely control an SDRplay SDR. This allows you have the feeling of tuning a vintage radio with the old fashioned knobs, whilst enjoying the features of a modern SDR.
Within the old radio enclosure they’ve managed to fit in a full Acer mini computer which runs the RSP on HDSDR. To allow the main tuning knob on the Marconi to tune the SDRplay they’ve used an Arduino controller, and an optical shaft encoder. As they intend for their hybrid to be completely keyboard-less, they’ve also added two UP/DOWN buttons to jump up and down the spectrum, buttons to choose the demodulation mode, and a new knob to control the zoom setting in HDSDR.
The project was sponsored by RS components and is intended to be used in the November 2016 Electronica event in Munich as an exhibit that celebrates the 80th anniversary of the expo. The idea is that the SDRplay-Marconi hybrid combines radio technology which would have been around during the first Electronica expo’s as well today’s modern SDR technology. There is a write up of the project available on the RS components designspark website.