Category: HF

Tech Minds: Reviewing the Malahit DSP1 SDR Receiver 50KHz – 2GHz

Over on the Tech Minds YouTube channel, Matt has uploaded a new review and demonstration of a Malahiteam DSP1 SDR Receiver 50KHz - 2GHz. This particular unit appears to be a Chinese clone unit which is actually called a 'Malahit SDR'. The Russian company Malahiteam makes the original units, and they come in a different enclosure and feature the full Malahiteam logo.

In the video Matt shows this version of the Malahit DSP1 in action, noting that the built-in speakers sound great and that RF performance seems to be good. He does however note that the enclosure is a bit cheap, being built out of PCB boards, and that the top encoder knob sometimes doesn't work properly. Overall Matt mentions that he probably wouldn't buy it at the current ~US$180 price point, noting that better newer models like the DSP2 and DSP3 already exist. 

Malahiteam DSP SDR Receiver 50KHz - 2GHz

Tech Minds: Review of the KiwiSDR 2

Earlier this year the KiwiSDR 2 became available for purchase and began shipping out to customers. The KiwiSDR 2 is an upgraded version of the original KiwiSDR with the main upgrades being an enhanced RF front end and the addition of a digital attenuator.

Over on the Tech Minds YouTube channel, Matt received his KiwiSDR 2 and uploaded a review and demonstration of the product. In the video, Matt shows the external ports of the KiwiSDR and discusses the differences between the KiwiSDR 2 and the original version. Matt goes on to show how to set up the KiwiSDR 2 and shows it receiving through it's web-based receiving software.

KiwiSDR is a 14-bit wideband RX-only HF software-defined radio created by John Seamons (ZL/KF6VO). The KiwiSDR has up to 32 MHz of bandwidth, so it can receive the entire 10 kHz - 30 MHz VLF/LF/MW/HF spectrum all at once. Other than the specifications, the main interesting feature about the KiwiSDR is that it is designed to be operated entirely as an online web-based SDR which is accessed over a network connection. Owners can optionally share their KiwiSDRs online with anyone who wants to access it, which also allows for interesting distributed applications, such as TDoA direction finding, which allows users to pinpoint the location of unknown HF transmissions such as numbers stations.

KiwiSDR 2 - A Standalone Software Defined HF Radio Receiver

KiwiSDR 2 Now Available For Purchase

Back in August 2023 we posted about the pre-announcement of the KiwiSDR 2, an upgraded version of the original KiwiSDR. Most of the upgrades are minor or due to some chips becoming EOL. The main upgrades are an enhanced RF front end and the addition of a digital attenuator. One change is also the manufacturing country. Instead of being manufactured in China, the KiwiSDR 2 is now manufactured in New Zealand.

The new KiwiSDR 2 can be purchased from kiwisdr.nz. Pricing is $648 NZD ($395 USD) for the full KiwiSDR 2 cape + Beaglebone and enclosure set. The cape by itself is also available for $484 NZD ($295 USD). Currently the second production run is selling, and a third production run is in progress. 

Previously the original KiwiSDR sold for $299 USD. Considering inflation, component changes and additions, and the change to a more expensive country to manufacture in, the price increase seems reasonable. 

KiwiSDR is a 14-bit wideband RX only HF software defined radio created by John Seamons (ZL/KF6VO). The KiwiSDR has up to 32 MHz of bandwidth, so it can receive the entire 10 kHz - 30 MHz VLF/LF/MW/HF spectrum all at once. Other than the specifications, the main interesting feature about the KiwiSDR is that it is designed to be operated entirely as an online web based SDR which is accessed over a network connection. Owners can optionally share their KiwiSDRs online with anyone who wants to access it, which also allows for interesting distributed applications, such as TDoA direction finding, which allows users to pinpoint the location of unknown HF transmissions such as numbers stations.

KiwiSDR 2 with BeagleBone and Enclosure Set

An HF Ham Radio SSB/AM/FM/CW Transmitter made from a Raspberry Pi Pico and not much more

Over on Hackaday we've seen a story about a Raspberry Pi Pico based software defined radio transmitter that is capable of transmitting SSB, AM, FM and CW anywhere between 0.5 - 30 MHz.

The design generates an oscillator signal using the Pico's Programmable IO. For AM/SSB it uses the PWM output pins to generate an RF envelope which gets mixed together with the oscillator using an analog multiplexor. A small microphone is also connected to the Pico for voice transmissions. The designer notes that the output power is far too low to be used on the air, but adding an output amplifier would help.

The software is all open source and provided on GitHub, and more information about the design can be found on the designer's '101things' website.

The Raspberry Pi Pico is a low cost microcontroller board, and we note it cannot run Linux like standard Raspberry Pi boards. This means that software like RpiTX cannot be used.

Build a Ham Transmitter with a Raspberry Pi Pico

A WSPR Monitor Running on an old Android TV Box with OpenWebRX and RTL-SDR

Thank you to Joseph IT9YBG for writing in and sharing with us his experience in getting Armbian and OpenWebRX running with an RTl-SDR V3 smoothly on an old A95X Android TV Box. These TV Boxes have an AMlogic S805 chip and Joseph writes that he is quite impressed by the performance of the chip.

To install the Armbian Linux operating system Joseph used the instructions from i12bretro and installed OpenWebRX after. Then together with his RTL-SDR Blog V3 dongle he turned the device into a cheap dedicated WSPR (Weak Signal Propagation Reporter) monitor allowing him to free up his Raspberry Pi 3 which was used for the task previously.

IT9YBG's Android TV Box converted into a WSPR monitor with an RTL-SDR Blog V3 and OpenWebRX
IT9YBG's Android TV Box converted into a WSPR monitor with an RTL-SDR Blog V3 and OpenWebRX

TechMinds: Demonstrating OpenWebRX Plus

In one of his videos from a few days ago Matt from the Tech Minds YouTube channel tests out OpenWebRX+, an unofficial fork of OpenWebRX. OpenWebRX is open source software which enables users to put software defined radios like RTL-SDRs on the internet, allowing people from all over the world to access the receiver if desired, or just letting yourself access it remotely if you want to keep it private.

OpenWebRX+ adds several additional decoders and features on top of the official version. In the video Matt demonstrates OpenWebRX+ running on a Raspberry Pi 4, with an SDRPlay RSPdx. He demonstrates the web GUI in action and shows decoding examples of the various decoders that OpenWebRX+ comes with.

OpenWebRX Plus - The ULTIMATE Web SDR Application

A Tape Measure Antenna for Receiving HF Numbers Stations

In his Hackaday.io post (and a post on the main Hackaday blog), Tom Farnell explains how he used two 10-meter tape measures combined with an RTL-SDR Blog V3 software defined radio to receive numbers stations in the HF bands. We want to add that this antenna isn't restricted to just numbers stations, and could receive many different types of shortwave and amateur stations on HF.

In his post Tom explains what numbers stations are and why they are interesting. In brief, a numbers station is a radio broadcast of a voice saying a bunch of numbers continuously. These stations are known to be espionage related, containing some sort of coded message for international spies to decode.

Tom goes on to show how the antenna is constructed. As HF antennas need to be long to get the best reception, Tom uses the long metal tape measure and attached it to the included dipole assembly that comes with the RTL-SDR to increase them to an appropriate length. 

Intercepting Spy Radio Messages With A Tape Measure

Testing the ATS25 Max-Decoder Receiver

Thank you for Manuel Lausmann for submitting his videos where he tests out and upgrades an ATS25 Max-decoder receiver. The ATS25 Max-decoder is a low cost portable HF receiver which has a large number of decoders built in such as RTTY, Hell, FT8 and FT4. Manuel notes that more decoders are still to come, such as SSTV. The built in decoders make it superior to it's predecessors the x1 and x2.

We note that the ATS25 Max appears to be around US$75 on Aliexpress, but these appear to be Max units without the "-decoder" add on. So if you are looking at purchasing one, please make sure to check that you are getting one with the text "max-decoder".

Manuel also notes that older models of the ATS25 can be retrofitted with a decoder PCB and converted into an ATS25 Max-decoder with a firmware update written by Bernhard Binns.

Note that Manuel's videos below are narrated in German, however the YouTube subtitle auto-translate feature works well enough to understand what is being said. In the first video Manuel demonstrates and reviews the ATS25 Max-Decoder, showing off some of the decoding features.

In the second video Manuel shows how to update an old model ATS25 in to the ATS25 Max by soldering on the decoder board.

Alter ATS25 umbauen zum max Decoder Teil 1 Die Hardware