Category: HF

Monitoring FT8, JT65, JT9 on Multiple Bands with Low Cost Single Board PCs

Thank you to Michael (dg0opk) who wrote in and wanted to share details of his full SDR monitoring system for weak signal HF modes. His setup consists of nine ARM mini PCs (such as Banana Pi's, Raspberry Pi's, and Odroid's), several SDRs including multiple RTL-SDR's, an Airspy Mini, FunCube Dongle and SDR-IQ, as well as some filters and a wideband amp. For software he uses Linrad or GQRX as the receiver, and WSJTx or JTDX as the decoding software, all running on Linux.

Michael also notes that his Bananapi FT8, JT65 and JT9 SDR monitor has been up and stably running continuously for half a year now. Bananapi's are lower cost alternatives to the well known Raspberry Pi single board computers, so it's good to note that a permanent weak signal monitoring system can be set up on a very low budget. Presumably even cheaper Orange Pi's would also work well.

With his setup he is able to continuously monitor FT8, JT65 and JT9 on multiple bands simultaneously without needing to tie up more expensive ham radios. His results can be seen on PSKReporter. A video of his RTL-SDR Raspberry Pi 3 decoding FT8, JT65 and JT9 can be found here.

Weak Signal Receiver Setup
dg0opk's weak signal receiver setup

Going Portable with the Airspy HF+, Raspberry Pi and 7-Inch Touch LCD

Over on the swling blog we've seen a post where contributor 'Tudor' demonstrates his Airspy HF+ running nicely on a Raspberry Pi 3, 7-inch touchscreen LCD, and USB power bank. The video shows GQRX running very smoothly on the Pi, and how the setup is able to receive various HF signals. Tudor writes:

I bought the RPi to use it as a Spyserver for my Airspy HF+ SDR.

My main radio listening location is a small house located on a hill outside the city and there is no power grid there (it’s a radio heaven!), so everything has to run on batteries and consume as little power as possible.

My first tests showed that the Raspberry Pi works very well as a Spyserver: the CPU usage stays below 40% and the power consumption is low enough to allow it to run for several hours on a regular USB power bank. If I add a 4G internet connection there I could leave the Spyserver running and connect to it remotely from home.

Then I wondered if the Raspberry Pi would be powerful enough to run a SDR client app. All I needed was a portable screen so I bought the official 7” touchscreen for the RPi.

I installed Gqrx, which offers support for the Airspy HF+. I’m happy to say it works better than I expected, even though Gqrx wasn’t designed to work on such a small screen. The CPU usage is higher than in Spyserver mode (70-80%) but the performance is good. Using a 13000 mAh power bank I get about 3.5 hours of radio listening.

On the swling blog post comments Tudor explains some of his challenges including finding a battery that could supply enough current, finding a low voltage drop micro-USB cable, and reducing the noise emanating from the Raspberry USB bus. Check out the post comments for his full notes. 

Airspy HF+ and Gqrx running on Raspberry Pi
Airspy HF+ and Gqrx running on Raspberry Pi

GridTracker Now Available on Windows, Mac and Ubuntu (Debian)

In early February we posted news about the release of a program called GridTracker. GridTracker is a live mapping program for WSJT-X which is a software decoder for low power weak signal ham communications modes such as FT8, JT4, JT9, JT65, QRA64, ISCAT, MSK144 and WSPR. Although these are low power modes, the protocols are designed such that even weak signals can potentially be received from across the world. Mapping the received signals can be interesting as it may give you an idea of current HF propagation conditions.

Previously GridTracker was Windows only software. However recently GridTracker was updated to now include support for Mac and Ubuntu (Debian) operating systems as well. This is great news as it makes it much easier to set up a portable GridTracker screen on a portable computer like a Raspberry Pi.

GridTracker Mapping out Weak Signal Communications.
GridTracker Mapping out Weak Signal Communications.

Video Tutorial on Decoding FT-8 and RTTY with an SDRplay RSP1A

Over on YouTube radio content creator Techminds has recently started a series that shows how to decode various signals using an SDR such as the SDRplay RSP1A. The first video explains what FT-8 is and shows how to decode it using the WSJT-X software. FT-8 is a modern digital HF ham mode that is designed to be receivable even in weak signal reception. However, the amount of information sent in a FT-8 message is small, so it is not possible to have a full conversation, and you can only make contacts.

In his second video Tech Minds explains RTTY and also shows how to decode it. RTTY is another much older mode that is used by the military as well as hams. To decode it he uses Digital Master 780 which is a program included in the Ham Radio Deluxe software.

Decoding FT-8 With WSJT-X And A SDRplay RSP1A SDR Receiver
Decoding FT-8 With WSJT-X And A SDRplay RSP1A SDR Receiver

Decoding RTTY With Digital Master And A SDRplay RSP1A SDR Receiver
Decoding RTTY With Digital Master And A SDRplay RSP1A SDR Receiver

Listening to SELCAL and the HF Air Band with an RTL-SDR

Over on YouTube content creator Tech Minds continues to upload informative RTL-SDR based videos, this time discussing SELCAL and the HF Air Band. For international flights it is common for aircraft to communicate with ground controllers and the parent company via the HF bands.

As radio communications are sparse, and the pilots obviously don't want to monitor noisy HF static for the entirely journey a system is required for signalling pilots when a ground station wishes to communicate with them. The system in use today is SELCAL which simply consists of transmitting a set of tones unique to an aircraft. When a correct SELCAL tone is received the aircraft system alerts the pilots that a radio voice communication is about to come through, allowing them time to get the radio in operation. 

Tech Minds' video explains this in a bit more detail, and shows some examples of HF air comms with SELCAL tones played.

Receiving HF Air Band With An RTL SDR Receiver - SELCAL
Receiving HF Air Band With An RTL SDR Receiver - SELCAL

Identifying Noise Sources in the Shack using an SDR and an Active Receive Loop

Over on YouTube user SignalSearch has uploaded a video showing how he uses an active magnetic loop antenna indoors to identify local noise sources. Magnetic loop antennas are directional, meaning that they receive best when pointing towards a signal. This means that they also receive noise better when pointed at a noise source.  In the video SignalSearch uses a W6LVP receive loop antenna and demonstrates noise being emitted from his lightbulb, and from a plug in Ethernet over powerline adapter, which are known to be huge sources of HF noise.

If you are interested in the noise produced by these Ethernet over powerline adapters then we did a previous post on this problem over here.

Using an Active Receive Loop Indoors & utilizing Software Defined Radio to identify noise sources
Using an Active Receive Loop Indoors & utilizing Software Defined Radio to identify noise sources

Receiving WSPR with an RTL-SDR V3 and with Automatic Band Changing

RTL-SDR V3 + Raspberry Pi WSPR Receiver
RTL-SDR V3 + Raspberry Pi WSPR Receiver

WSPR (pronounced "Whisper") is short for Weak Signal Propagation Reporting, and is a HF ham mode typically run on very low power levels such as 1W. The data from WSPR reception can be used to determine how good or bad HF propagation is currently around the world as each WSPR message contains a callsign, 6-digit locator and the transmit power level used. Received messages are all reported to the internet and can be viewed on an online map at http://wsprnet.org/drupal/wsprnet/map.

With an RTL-SDR V3 running in direct sampling mode it is possible to receive and decode these messages on a Raspberry Pi 3 using the WSPRD software.

Over on his website IT9YBG has uploaded a tutorial for a method that allows the WSPRD software to automatically change bands depending on the time of day. The method simply uses the crontab in Linux to automatically run a script that stops and then restarts WSPRD on a new frequency at certain times of the day. This is useful because different WSPR bands tend to become active at different times of the day due to changing HF propagation conditions.

WSPR messages received from all over the world.
WSPR messages received by IT9YBG from all over the world.

Decoding Morse Code and Weather Faxes with an RTL-SDR

Over on the YouTube channel Tech Minds the presenter has uploaded two new RTL-SDR based tutorial videos. The first video gives a bit of background and shows how to decode Morse code with an RTL-SDR. He uses SDR-Console V3 and the Morse code decoder CwGet. With this he's able to decode a few calls from some ham radio operators.

In the second video Tech Minds shows how to decode Weather Fax with the RTL-SDR. Weather faxes are images of weather charts sent over HF frequencies. In the video he uses SDR-Console and SeaTTY to do the decoding and demonstrates reception of an example fax.

The Real Matrix - Decoding Morse Code Using An RTL SDR Receiver
The Real Matrix - Decoding Morse Code Using An RTL SDR Receiver

Receiving HF Weather FAX Using An RTL SDR Receiver
Receiving HF Weather FAX Using An RTL SDR Receiver