A Demonstration of RSPDuo Diversity Being used to Cancel Local Interference

SDRPlay have recently published a video demonstrating how the new RSPduo diversity feature in SDRUno can be used to cancel local interference.  The SDRplay RSPDuo is a 14-bit dual tuner software defined radio capable of tuning between 1 kHz - 2 GHz. It's defining feature is that it has two receivers in one radio, which should allow for interesting phase coherent applications such as diversity. The RSPDuo's diversity feature allows us to either combine two antenna signals together for an up to 3 dB increase, or for removal of an unwanted noise source via subtraction of signals.

In the video they show a broadcast AM signal that has it's SNR reduced by being on top of a local electrical noise source. The use a Bonito Mega-dipole on tuner 1, and a Bonito Mini-whip on tuner 2. The Mini-whip appears to receive the local interference stronger, so can be subtracted away from the Mega-dipole's signal with the diversity function. The result is improved SNR, and the noise is almost entirely cancelled.

There are 2 very practical applications for diversity software. The first is MRC (Maximum Ratio Combination) Diversity which, in order to be effective, needs two antennas presenting the same signal with some degree of diversity. Then there is this second impressive application which is becoming more and more useful due to the growing number of domestic sources of interference.

This is possible in an RSPduo, due to the coherent nature of the combined tuner streams being presented to the computer for processing.

Using Diversity in SDRplay's SDRuno to Cancel Local Interference

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Weather Satellite NOAA 15 Appears to have Failed (Again)

Back in April 2018 we posted how the NOAA-15 APT weather satellite that many RTL-SDR users enjoy receiving images from was having problems with it's scan motor resulting in image errors. The satellite recovered from that problem, but today the problem appears to be back and in a much worse way now.

Users on Reddit and Twitter have reported bad images coming in from NOAA 15. Over on Reddit u/rtlsdr_is_fun has provided a post showing an example of a corrupted image, and also provided an IQ and Audio file. On his blog [Karsey] has also posted some interesting looking corrupted images that he's received.

Corrupted NOAA-15 Image Received by [Karsey]
Corrupted NOAA-15 Image Received by [Karsey] (See his post for the full sized images)

NASA have put out a statement indicating that yet again it is a problem with the scan motor, and the problem could be permanent.

The NOAA-15 AVHRR Scan Motor current began showing signs of instability at approximately 0400Z on July 23, 2019. At about 0435Z the current rose sharply to about 302mA where it has remained. Scan motor temperature began rising about the same time and is currently steady at ~26M-0C. Black body temperatures dropped sharply at about the same time. The instrument appears to no longer be producing data.
This behavior is consistent with a scan motor stall, but requires further investigation. Options for recovery are limited.

Having been launched in 1998 with a minimum spec of 2 years operation, NOAA-15 has already well outlived it's time and may finally be failing for real. We hope it will recover, but if not we should be thankful that Russian weather satellite Meteor M2-2 is now fully operational and transmitting beautiful high resolution images.

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Atomic Radio: Quantum Laser Based Radio Reception

Software defined radio (SDR) is a relatively new technology that has impacted the world of radio technology in many ways. But beyond SDR, there are still some other very interesting radio technologies being worked on, such as "Atomic Radio" a.k.a "Quantum Radio".

Atomic radio is essentially an idea that makes use of how special "Rydberg" atoms can modulate a laser beam when radio waves pass through them. A photo diode is then used to optically detect the radio wave from the modulated laser. This way of receiving requires no traditional radio circuits like amplifiers, mixers, and of course no antenna, so in theory the radio signal could be received with significantly less noise and with the highest possible SNR.

If you're interested in learning more about Atomic Radio, Hackaday recently ran an excellent article where they describe the concept and science behind it in more depth. They also go into some recent studies where scientists showed that they were able to receive two signals at once, and mention how one paper describes an extremely wideband Atomic Radio that can receive from the C-Band to the Q-band (4 GHz to 50 GHz).

Hackaday's Article is a Great Introduction to Atomic Radio
Hackaday's Article is a Great Introduction to Atomic Radio
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Slow Scan Moon Bounce Event for 50th Anniversary of the Moon landing

Fifty years ago Neil Armstrong became the first man to step foot on the moon. This weekend on June 20th and 21st 2019 Amateur Radio operators at the [PI9CAM] team have been transmitting Slow-Scan Television images in commemoration of this historic event at the Dwingeloo radio astronomy station in the Netherlands. This station is the oldest rotatable 25-meter radio telescope in the world. 

Dwingeloo radio astronomy station
Dwingeloo radio astronomy station
An EME SSTV Image
An EME SSTV Image

Slow-Scan Television is a method often employed by ham radio operators to send photos over radio waves. You may be familiar with this from some of our previous articles on the SSTV event held by ARISS for the International Space Station.

Station [S1NDP] has previously sent slow-scan EME images between the PI9CAM team and himself. These images can potentially be heard by anyone within line-of-site with the moon during the operation of this event.

The team transmit in the 23cm band at a frequency of 1296.11 MHz, according to the ARRL even a 2.5 to 3meter dish should be enough for reception assuming you have a 23cm feed for your dish. It will be interesting to see what photos are heard by the end of this event.

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Weather Satellite Meteor M2-2 Now Transmitting Images

Reports from Reddit and Twitter are in that the recently launched Meteor M2-2 weather satellite is now functional and broadcasting images at 137.9 MHz. A few people have noted that the reception quality appears to be better than the older satellite.

Thank you to Happysat whose also provided the following information that can be used to receive the images. It appears that a slightly modified version of LRPTDecoder is required:

This version of LRPTDecoder was used to test/debug OQPSK with Meteor M-N2-1 in 2014, it will work on Meteor M-N2-2.
The ini file attached in the archive is processed manually from s files.
Buttons 72K and 80K respectively for the modes “without interleaving” and “with interleaving”.
Also in the archive there are examples for other modes.

Transmissions on LRPT with a OQPSK Modulation are expected tomorrow on most probably 137.900MHz.

Make sure you have version 1.9 of the Meteor QPSK Plugin running in SDRSharp.
http://rtl-sdr.ru/uploads/download/meteor.zip

Changelog:
Optimized QPSK demodulator, OQPSK signal for receiving current and future Meteor.

For people running Tracking DDE Client Plugin make sure you have the following entries in the scheduler:

METEOR-M2_2

radio_Start
radio_modulation_type<wfm>
radio_center_frequency_Hz<138380050>
radio_frequency_Hz<137900000>
radio_bandwidth_Hz<90000>
OQPSK_demodulator_Start
send_tracking_frequency_On

Edit to your path! for MeteorGIS Custom ini file start_programm_Path<C:\Meteor\MeteorGIS\MeteorGIS.exe>

Edit to your path! for MeteorGIS Custom ini file start_programm_Path<C:\Meteor\MeteorGIS\MeteorGIS_M_N2-2.bat>

Edit to your path! Without MeteorGIS start_programm_Path<C:\AMIGOS\run.bat>

send_Tracking_Frequency_Off
OQPSK_demodulator_Stop
radio_Stop

Download:

https://cloud.mail.ru/public/2Se9/9bj36m6AP

Mirror:

http://happysat.nl/2015.3.20.15.zip

Спасибо Олегу, Нцомз и Роскосмосу!

Happysat

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PICTOR: An Open Source Low Cost Radio Telescope based on RTL-SDR

PICTOR is an open source and open hardware radio telescope that aims to promote radio astronomy on a budget. It consists of a 1.5 meter parabolic dish antenna, 1420 MHz feedhorn, a two stage low noise amplifier (LNA), high pass filter, and from what we gather, an RTL-SDR. Future designs may also use higher bandwidth SDRs. Currently there doesn't seem to be much information about the build and exact components used in their design, but we're hoping that those details will come in time.

The radio telescope allows a user to measure hydrogen line emissions from our galaxy. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). The emissions themselves are very rare, but since our galaxy is full of hydrogen atoms the aggregate effect is that a radio telescope can detect a power spike at 21cm. If the telescope points to within the plane of our galaxy (the milky way), the spike becomes significantly more powerful since our galaxy contains more hydrogen than the space between galaxies. Radio astronomers are able to use this information to determine the shape and rotational speed of our own galaxy.

PICTOR also has a very interesting web based interface which can be used to let users from anywhere in the world access the telescope and log an observation. The first PICTOR telescope is currently online and observations can be created simply by going to their website, and clicking on the "Observe" link. Users can then enter the frequency and other parameters for their observation, and the resulting graph will be emailed to you after the observation. The software source is available on their GitHub page, and is based on a GNU Radio flowgraph and Python plot script.

For more information about PICTOR, logging an observation, and radio astronomy in general, we recommend checking out their PDF guide. We test ran a short observation at the hydrogen line frequency, and we received a graph with the hydrogen line peak clearly visible (spliced in to the photo below). We note that the wavy shape is due the to shape of the filters they used.

PICTOR Radio Telescope
PICTOR Radio Telescope
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A Low Cost 2.4 GHz Downconverter from off the Shelf Dev Boards

Over on GitHub Ian Wraith has released his design and microcontroller code for a low cost 2.4 GHz downconverter circuit. A downconverter is a hardware device that shifts the signals that it receives into a lower frequency band. This is useful in the case of RTL-SDRs and Airspy SDRs, as their maximum frequency range is only 1.7 GHz. Ian's 2.4 GHz downconverter reduces those 2.4 GHz signals down to 1 GHz, which can then be received with his Airspy.

Rather than designing a circuit from scratch, Ian's design makes use of several very cheap Chinese evaluation/development boards that he found on eBay. It costs of a mixer board, oscillator board, and an STM32 development board for controlling the oscillator board via SPI. The whole set of hardware cost him less than £30 (~37 USD).

After spending some time working through the difficulties in programming the SPI interface on the STM32 board, he was able to get the downconverter circuit fully working. He notes that he's been able to receive WiFi, Zigbee, Bluetooth and ISM band signals at 2.4 GHz, as well as 3G and 4G cellular signals at 2.6 GHz.

Ian Wraith's Downconverter consisting of three off the shelf cheap Chinese eBay boards.
Ian Wraith's Downconverter consisting of three off the shelf cheap Chinese eBay boards.
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SignalsEverywhere: Improving HF Reception with Impedance Matching

This week on the SignalsEverywhere YouTube channel host Corrosive explores why impedance matching matters when trying to obtain the best reception possible. To do this he reviews the NooElec 1:9 Balun, which is designed to convert the (roughly) 450 Ohm impedance of a long wire antenna or ladder line dipole back down to 50 Ohms, which is the standard impedance that an SDR expects. Small amounts of impedance mismatch are negligible for RX, but larger mismatches can result in poor reception.

SDR Nooelec 1:9 Balun | Why Impedance Matters in Radio

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