The Radio Spectrum Processor (RSP) by SDRPlay is a receive only software defined radio with a 100 kHz to 2 GHz range (with a small gap at 380 MHz to 430 MHz), a 12-bit analogue to digital converter (ADC) (~10.4 ENOB), 8 MHz bandwidth and a bank of several switched front end filters.
Previously the SDRPlay RSP was priced at $299 USD, however they have just halved this price down to $149 USD plus tax and shipping. At this price point we think the SDRPlay is a very good competitor to the Airspy SDR which seems to be the more popular option priced at $199 USD, especially if you are interested in listening to the HF bands without the need for an upconverter.
Recently we posted about some SDRPlay reviews which are all favourable.
Over on YouTube user max30max31 aka IZ5RZR has uploaded a video that shows a faster method for decoding Meteor M2 weather satellite images on a Windows system. The Meteor-M N2 is a Russian weather satellite that transmits images using the LRPT protocol at around 137.1 MHz with can be received with an RTL-SDR. Compared to NOAA satellite APT images, LRPT images are much higher in resolution.
Normally, decoding Meteor M2 LRPT images requires a post processing step which involves the use of Audacity, an audio editing suite to reduce the recorded IQ files sample rate. However, with the recently released decimation SDR# drivers the Audacity step can be avoided by using a an appropriate decimation factor (8 at 1.024 MSPS) when recording the LRPT signals IQ data.
Over on YouTube user Frederik De Bleser has uploaded a video showing his new open source toolkit called Frequensea which can be used for visualizing the electromagnetic spectrum with an RTL-SDR or HackRF. The software allows you to visualize the output as an FFT spectrum in various 3D display modes and is even compatible with the Oculus Rift, a virtual reality headset.
Frequensea can be downloaded from https://github.com/fdb/frequensea, and it currently has installation instructions available for OSX, Ubuntu and the Raspberry Pi.
Visualizing the electromagnetic spectrum with Frequensea
Android app programmer Nikos recently wrote in to let us know about his new app called “Track your flight Europe”. His app can be used together with an RTL-SDR and USB OTG cable to track aircraft via ADS-B. The difference between Nikos’ app and other similar ADS-B apps is that his app is specifically designed for tracking the aircraft you are flying in by providing an offline map which does not require an internet connection to display.
By using an RTL-SDR dongle together with a low cost noise source it is possible to measure the response of an RF filter. Also, with an additional piece of hardware called a directional coupler the standing wave ratio (SWR) of antennas can also be measured. Measuring the response of a filter can be very useful for those designing their own, or for those who just want to check the performance and characteristics of a filter they have purchased. The SWR of an antenna determines where the antenna is resonant and is important for tuning it for the frequency you are interested in listening to.
Using just a noise source and RTL-SDR dongle it is possible to determine the properties of an RF filter. In our experiments we used the following equipment:
The BG7TBL noise source is a wideband noise source that can provide strong noise over the entire frequency range of the RTL-SDR. It requires power from a 12V source which can be obtained from a common plug in power supply. It also uses an SMA female connector, so you may need some adapters to connect it to your filter under test (adapters can be found cheaply on Ebay). Finally a quick warning: be careful when handling the circuit board after it has been powered for some time as some of the components can get very hot. Note that if the Ebay store runs out of these there is also a seller on Aliexpress with some available, just type "noise source" in the search bar.
Peters first results show that the R820T2 has better reception and less spurious features at frequencies above about 1.45 GHz and improved frequency stability (with the newer R820T2 dongles that use the SMD oscillator). His second set of results explore issues that are more closely relevant to radio astronomy including observed spectra, Allan variance (frequency stability) tests and determining the shape of the R820T/2 internal bandpass filter.
In the conclusion of the paper Peter writes:
Two Newsky RTL2838U dongles were tested, the R820T2 device against the R820T. The evaluation results in a clear preference for the new RTL2838U/R820T2 dongle. In the L-band the new dongle is at least 2.7 dB more sensitive. According to the radiometer equation the effective system temperature is reduced by almost 50%. Most important for reliable radio astronomical observations are stability issues. Allan variance tests have shown that the R820T2 dongle is far better then the older version. The stability is comparable to that of professional radio astronomical devices. The tests have shown that using the full bandwidth of the RTL-SDR devices results in spurious baseline ripples. For a good performance it is recommended to use the dongles at reduced bandwidth. rtl power with the crop option -c 0.5 appears to be a good choice.
Broad band performance of the R820T dongle (top) and R820T2 (bottom)
Recently amateur radio astronomer Jim Brown used an RTL-SDR dongle together with a Ham-it-up upconverter and preamp to capture noise bursts from the planet Jupiter. Not much information about his observations are available yet as he has not yet made a write up, but he has given the image of the noise burst shown below to Jim Sky, programmer of RTL Bridge and Radio-Sky Spectograph which is some of the software used to capture the noise bursts. We will make another post in the future if Jim Brown does a write up.
Jim Sky has also updated his RTL Bridge software to use Oliver Jowetts patched drivers, which allow the RTL-SDR to receive below its usual 24 MHz limit.
Upconverters are often used to extend the RTL-SDR dongles minimum receivable range down to the HF, MF and LF bands. They are available for purchase commercially, or you can build your own, which is what Tomasz of mightydevices.com has done.
By using a low cost mixer IC chip called the NE612 and some passive components Tomasz was able to build a low cost upconverter for his RTL-SDR. His upconverter uses a 100 MHz crystal oscillator that brings frequencies between 0-30 MHz up to a range of 100 – 130 MHz, which is in the receivable range of the RTL-SDR. The upconverter circuit was also designed to be able to provide inline power for a active (powered) Miniwhip antenna. Tomasz’s post explains the design choices and theory behind his circuit design.
