Recently an RTL-SDR.com reader named Jon wrote in and wanted to share his project called FPGA-TX. FPGA-TX is software that provides low-cost SDR transmit capabilities on an FPGA. It works in a similar way to RPiTX which is by simply turning the GPIO pins on and off very quickly in such as way that it generates any desired AM/FM/SSB transmission. These methods are crude and require external analog filtering, but can be used for creating almost any sort of RF transmission at a wide range of frequencies extremely cheaply. These sorts of cheap transmitters are great companions to low cost SDR dongles like the RTL-SDR.
Jon’s project runs on FPGA boards and currently supports the Digilent Nexys 4 and Digilent CMOD A7 ($75) FPGA boards. An FPGA is an integrated circuit that can be easily reconfigured to implement various different digital circuits.
FPGA-TX can transmit at frequencies of up to 400 MHz and current supports AM, FM, LSB, USB, Wideband FM and Wideband FM Stereo transmission modes. It runs on Linux. The FPGA transmitter has been tested combined together with an amplifier and filter. It can also interface with a GPS unit for clock calibration.
An FPGA Based Transmitter. In the photo: FPGA, Amplifier, Filter, Attenuator, TX/RX Switch.The FPGA-TX Ubuntu Interface.
Over on YouTube user Tomi Simola has uploaded a video showing his servo based Outernet satellite antenna tracker. Outernet uses L-band geostationary satellites which means that they are at a fixed position in the sky. Optimal reception of the Outernet and other L-Band satellite signals can be obtained by pointing the patch antenna towards the satellite.
Tomi wanted an easy way to remotely switch the antenna to point at one of two geostationary satellites, Alphasat at 25E which has the Outernet signal and Inmarsat at 64E which has more services like AERO and STD-C. Another potential use of his tracker might be for tracking L-Band satellite while in a moving vehicle such as a car or boat.
To automatically point the Outernet L-band patch antenna Tomi used a commonly found Pan-Tilt servo mounted inside an waterproof enclosure. On the servo is a 3D printed mount which the patch antenna is attached on. An Arduino Nano with Bluetooth module allows control of the servo.
Last week the Airpsy team gave us the opportunity to give away some prizes, so we started a comment competition. The prizes were an Airspy R2 + SpyVerter, Airspy Mini + SpyVerter and SpyVerter. The competition closed yesterday with over 500 entries, and the winners have now been selected via random.org. Congratulations to the winners below:
Larry (Airspy R2 + SV) If I am going to win something from this one stuff, me build internet remote receiver on hill in central Europe (CZ) for all readers and fans of rtl-sdr.com website, generally for all RTL SDR enthusiasts….. :-))) Pour Felicitér 2017 Larry (Ladislav)
kevin (Airspy Mini + SV) been a ham a couple years now. their are so many uses for sdr’s ! it’s so cool. just looking down the list of others comments, i was like ‘oh ya’ forgot about that idea. awhile back we did a demo at our ham club with a el cheapo sdr and it sparked some interest , would like to play around with some of the newest toys, worlds of diff in capabilities. ultimate goal is to find the right one for the clubs emergency trailer. seeing the bands and whats going on, is priceless
Josh (SpyVerter) I’d love to finally get into the HF band!
If you’re a winner please check your email address for the competition winner email.
The competition produced some very interesting comments that show the diversity in projects that can be performed with a SDR receiver and we strongly encourage you to read through the comments if you are looking for project ideas.
If you didn’t win, sorry! Better luck next time. But please continue to follow us on Facebook and Twitter as we will have more competitions and more prizes to give away later in 2017!
Over on YouTube user Mile Kokotov has uploaded two new videos that show both the SDRplay RSP1 and RSP2 receiving VLF, LF and AM BC signals. The SDRplay RSP1 is a 12-bit SDR that can receive from about 10 kHz – 2 GHz. Recently the RSP2 was released which is an upgrade over the RSP1 with additional filters and features. On this blog we did an initial review of the RSP2 and found mostly improved performance over the RSP1.
Mile writes about the signals he receives:
Antenna on RSP2 is connected to its Hi-Z port.
Here are some information about signals in this video:
60 kHz Time signal from NPL is a radio signal broadcast from the Anthorn Radio Station near Anthorn, UK. The signal, also known as the MSF signal is broadcast at a highly accurate frequency of 60 kHz and can be received throughout the UK, and in much of northern and western Europe. (But I am receiving it in Macedonia) The signal’s carrier frequency is maintained at 60 kHz controlled by caesium atomic clocks at the radio station.
77.5 kHz Time signal is German DCF77 longwave time signal and standard-frequency radio station. The highly accurate 77.5 kHz carrier signal is generated from local atomic clocks that are linked with the German master clocks.
On 295 kHz there is NDB (Non directional Beacon) from Alexander The Great Airport near Skopje (about 80 km from my home)
On AM Broadcast Band (530 kHz – 1620 kHz) you can see how many AM stations are on the spectrum display (with 9 kHz raster) receiving here at my home with Mini-Whip antenna which is only 10 cm long!
The first video shows reception with a Mini-Whip, and the second with a Delta Loop. We don’t see much difference in reception between the RSP1 and RSP2 in these videos but viewers with more sensitive ears may be able to tell us if they notice any differences.
SDRplay RSP1 and RSP2 receiving VLF LF and AM BC with Mini-Whip
SDRplay RSP1 and RSP2 receiving 60 kHz and 77.5 kHz Time signals in Macedonia
A downconverter is a circuit that allows the RTL-SDR to receive frequencies above its maximum frequency range of about 1.8 GHz. It works by converting all higher frequencies down into a lower frequency which can be received by the RTL-SDR. It is the opposite of an upconverter which is used to receive HF frequencies on an RTL-SDR. In the past the Outernet project was working on a commercial downconverter product for the RTL-SDR, but they had to unfortunately put an end to that project as the costs were not economical.
But now over on GitHub Raziel Einhorn has uploaded plans for his open hardware 1.5 – 3 GHz downconverter which is code named Nigun (Melody). Currently the design has just about been completed, and he is planning to order the first prototype this January. The main component appears to be the ADRF6612 RF mixer which is controlled by an ATSAMD21E18A ARM microcontroller. On the GitHub page he explains the main properties as:
Dynamic LO – LO will be determined by the user and programmed by the MCU
Almost no filtering – will leave this challenge outside of this project scope
Power up and programming via micro-usb connector. Should be able to power up from a USB power-pack (but probably not from a computer port)
Highest RF frequency will be 3GHz
Product also features a VCO for signal-generation purposes. VCO support should be 200-2700MHz
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.
BY70-1 is a Chinese amateur Cubesat satellite which was recently launched on December 29, 2016. It is expected to stay in orbit for only 1 – 2 months due to a partial failure with the satellite releasing into an incorrect orbit. The purpose of the satellite is for education in schools and for amateur radio use. The receivable signals include an FM repeater and BPSK telemetry beacon both of which can be received at 436.2 MHz. The telemetry beacon is interesting because it also transmits images from an on board visible light camera. These signals can easily be received with an RTL-SDR or other SDR with an appropriate antenna.
Over on his blog Daneil Estevez has been posting about decoding these telemetry images. He’s been using telemetry data collected by other listeners, and the gr-satellites GNU Radio decoder which is capable of decoding the telemetry beacons on many amateur radio satellites. So far the decoded images haven’t been great, they’re just mostly black with nothing really discernible. Hopefully future decodes will show better images.
If you want to track the satellite and attempt a decode, the Satellite AR Android app has the satellite in its database.
Not many people seem to have gotten telemetry decodes or images yet, but below we show an image decoded by @bg2bhc on Twitter.
Vivaldi’s are linearly polarized broadband antennas that have a directional radiation pattern at higher frequencies. The high end SDR manufacturer RF Space produces their own Vivaldi antennas made from PCB boards which they sell online. The larger the antenna, the lower its receiving frequency, and ones that go down to about 200 MHz are almost the size of a full adult person. But all sizes receive up to 6 GHz maximum. Typically smaller versions of Vivald antennas have been used in the past for L-Band satellite reception.
Over on his blog KD0CQ noted that he always had trouble trying to purchase a Vivaldi from RF Space because they were too popular and always out of stock. So he decided to try and build his own out of PCB boards. On this page he’s collected a bunch of Vivaldi cutout or transfer images. On his second page he shows a Vivaldi antenna that he built out of PCB material, just by using scissors and semi-rigid coax. With the Vivaldi placed outdoors he’s been able to successfully receive and decode L-Band AERO on his Airspy Mini even without an LNA.
KD0CQ writes that he’ll update his blog soon with more results.
Simple Vivaldi antenna by KD0CQ cut out of PCB board.
