Tagged: HF

Claude VOACAP Skill: Ask Claude About Live Ionospheric Propagation Predictions to Optimize DX

Thank you to Reid Crowe for submitting his project, "voacap-skill." This skill for Claude Code AI (a frontier LLM) lets Claude access and use the latest VOACAP ionospheric propagation data in conversations.

Instead of manually filling out a form for each prediction and analyzing the results yourself, with the voacap-skill, users can ask Claude questions like, "What's the best band to reach Tokyo from Columbus, Ohio around 0300Z in October?" and Claude will run a VOACAP prediction in the background and return an answer. Reid explains:

If you've ever used VOACAP, VOACAP Online, or watched a contest DXpedition plan its band schedule, you already know the engine underneath this: it's the same NTIA/ITS point-to-point HF prediction model that's been the industry standard for propagation forecasting since the 1980s. It takes a transmitter location, a receiver location, a month, and a sunspot number, and tells you — for every hour of the day and every frequency you care about — how reliable that circuit is likely to be.

voacap-skill takes that engine (via voacapl, the modern Linux/GFortran port, on macOS/Linux, or the native NTIA/ITS Windows engine on Windows) and wires it into Claude Code as a "skill" — a capability Claude can reach for on its own.

The skill is free and open-source, with the code available on GitHub. Below, Reid provides some more examples of what you can ask Claude once it has access to VOACAP data.

Testing WSPR HF Propagation with a Raspberry Pi 3B+ and TAPR Shield Running WsprryPi

Thank you to Simone Spadino (SWL ID I8926BA), who wrote in to share his low-cost WSPR setup. WSPR (Weak Signal Propagation Reporter) is an amateur radio mode designed to test propagation paths using very low-power transmissions, with receiving stations reporting spots in real time to the WSPRnet map.

Simone's setup consists of a Raspberry Pi 3B+, which can be made to modulate a square wave RF signal on one of its GPIO pins via the WsprryPi software. Because a square wave generates many harmonics, he used the 20m WSPR shield from TAPR, which provides a low-pass filter to remove them. A dipole made from simple electrical monopole wire was connected to the shield via 50 ohm coax, and the signal was transmitted at 14.0971 MHz.

Transmitting from his rooftop in the center of Bari in southern Italy, Simone had his beacon received in England, Finland, Cyprus, and the Canary Islands, all more than 3100 km away. He repeated the experiment a week later with similar results. This is a reminder of how far low-cost hardware can transmit with a resilient protocol like WSPR.

Simone's WsprryPi Setup
Simone's WsprryPi Setup
WSPR Range with the Raspberry Pi 3
WSPR Range with the Raspberry Pi 3

Building an “HF Helper” for Improving RTL-SDR HF Reception

Over on YouTube Amateur Radio VK3YE has uploaded a video showing his 'HF Helper' project. The HF Helper is a tunable HF filter and attenuator that helps improve HF reception when in the presence of strong overloading signals. VK3YE writes:

Using an RTL-SDR.COM dongle (genuine model V4) and a computer with SDR Sharp you can get quite good reception of HF signals. However reception can sometimes be spoiled by overload from signals on or away from the desired reception frequency. The 'HF Helper' presented here can reduce these problems. And you can use it in conjunction with a QRP transmitter to form a simple transmitting station.

RTL SDR HF Helper improves reception

Also as a bonus, in a related video VK3YE also shows the RTL-SDR Blog V4 being used on SDR Touch on an Android phone for portable HF, VHF and UHF reception.

Hear HF VHF UHF on an Android phone

Tech Minds: Using the RK888 MK2 to Receive the Entire HF Band

In one of his latest videos Matt from the Tech Minds YouTube channel tests out the RX888 MK2 software defined radio at HF frequencies. Matt notes that while the bandwidth of this SDR is limited to 10 MHz at VHF/UHF, you can actually use it in direct sampling mode to achieve a massive bandwidth of 64 MHz, allowing you to receive the entire HF band at simultaneously.  

In his video, Matt uses SDR-Console V3 and he shows the entire HF band being received at once. He also shows the SDR-Console V3 matrix bands organizer, which allows you to create multiple windows of zoomed-in spectrum. That combined with the multi-receiver feature could allow you to have multiple audio outputs for digital decoding across the HF band.

Amazing! ALL HF Bands at the SAME time with the RX888 Mk2

An Atmega328 + SI5351 Based WSPR Beacon

Thank you to Ihar Yatsevich for writing in and sharing with us his open-source WSPR beacon project. The WSPR beacon consists of a custom PCB with ATMega328 microcontroller, GPS module, single transistor amplifier, and Si5351 with TCXO.

The result is a very simple, portable WSPR beacon that can be heard all over the world. However, it appears that no band filters are built into this, so you will need to add a bandpass filter for the WSPR band that you are using.

WSPR (Weak Signal Propagation Reporter) (pronounced "whisper") is an amateur radio digital HF mode designed to be decodable even if the signal is received with very low power. Because of this design, even low-power transmitters can be received from all over the world. It can also be used to help determine HF radio propagation conditions as WSPR reception reports are typically automatically uploaded to wsprnet.

If you are interested, Ihar has written about his project in more detail over on Reddit. 

Ihar's Microcontroller Based WSPR Beacon
Ihar's Microcontroller Based WSPR Beacon

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

Tech Minds: Testing a High Impedance Amplifier for Software Defined Radio

Antenna impedance matching is important for antennas and software defined radios as impedance mismatches can result in poor reception. For transmitting SDR's the situation is more dire because impedance mismatches can actually damage the transmitting hardware or at least cause high power efficiency losses.

Over on his YouTube channel Tech Minds has uploaded a video where he tests out a battery powered HF high impedance amplifier for software defined radios. The amplifier is designed to be used with long wire antennas on the HF bands as these antennas typically have high impedances which don't match the 50 Ohm impedance that most SDRs expect to see. This device is an amplified alternative to using a passive unun.

The results in his video show that the signal to noise ratio is indeed boosted when the impedance matching amplifier is used. Later the device is opened to show the battery, charging management chip and amplifier chip.

High Impedance Amplifier for Software Defined Radio

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