JTTY - new mode for keyboard short message chat on HF

There's an interesting new mode coming in WSJT-X 3.2 that support short text messages over HF with the weak-signal performance of FT8 but without the need for time synchronisation. 

At the time of writing it's not quite out yet but it's in the release candidate of WSJT-X 3.2 so it won't be long.

Stephen, VK2BLQ, drew my attention to it and we had a chat between Melbourne and Sydney (714km {for Americans, sorry, I don't know how many football fields that is}).

We both reduced power to 1W and were able to talk without any problem.

Leaving it running on 40m I can see quite a bit of activity (click the image at left to see more).

It's great to have modes that work without the need for second accurate time synchronisation as this open the door to portable operation without internet.

Recently I've also been playing with RattleGram which is a similar idea of short messages over radio. There are apps for Android and iOS. It seems to be mostly used on VHF/UHF FM radios and probably isn't ideal for HF conditions.

I do miss the days of PSK31 when I used to have fascinating long form text contacts.

Phase nulling direction finder for fox hunting

Our club is holding a fox hunt in a few months. We have a few portable UHF beam antennas but I thought I'd try a simple design that uses the phase difference between two sense antennas. It's called a HANDI-Finder and was described in QST in 1993.

It uses a CD4047 oscillator divider to make a nice square wave and two diodes to mix the incoming signals. In my case the oscillator is at around 600Hz. When the phase is equal no tone is heard, otherwise you hear the tone in a receiver tuned to the frequency you're hunting. Here's the board:

To try it out I used a NanoVNA to generate a CW signal. Here's a demo:

It's available as a kit but they kindly make the circuit easy to find here. See https://handi-finder.com/ for full information.

Cleaned the work bench - why is it so damn hard?

My electronics work bench seems to descend in to entropy of its own accord faster than I can deal with it. Part of the problem is my short attention span - I start new projects before finishing the current ones.

I've had "clean shack bench" on my daily Reminder list, haunting me for months. Finally, over two days, I've taken drastic action.

Part of the problem is all those components, plugs, sockets, adapters, and bits of wire fall between not useful enough to have a proper box to go in and not useless enough to go in the bin.

My radio shack is quite small - probably a good thing - like a gas, junk expands to fill the available volume.

Cleaning up also triggers the mind and it's hard not to see something and start tinkering with it again.

Anyhow, I'm pleased that it looks good enough to work on again.

Built another NE602/LM386 Direct Conversion Receiver

In recent months I've been off in the land of software development and have been sadly ignoring the electronics workbench. To get me back in the mood I built another instance of the simple direct conversion receiver using two ICs described in Experimental Methods in RF Design.

NE602 mixer chips are a bit hard to find and the only ones I have are surface mount so you can see it on a little carrier board above. This design uses the on-chip oscillator. My tuning is extremely sensitive and will need some padding to give me band spread of just the 40m band. At this point I haven't tuned the front end and it's undoubtably way off so the receiver is quite deaf.

In the past I've built the, all discrete component, Soldersmoke Direct Conversion Receiver. That project is much more challenging than this little one but each has it's good ideas. I'm thinking of bringing over the PTO from Soldersmoke to this design just for fun (or perhaps over-thinking it and adding an Si5351 VFO!).

Here's the schematic.

(Click to enlarge).

Tech Talk on ABC Radio - AI dangers and opportunities

AI is moving beyond being a tool we use into systems that can make decisions and act autonomously. There are growing questions about how much control we have over them. 

Prime Minister Anthony Albanese in the US talking AI at the United Nations, and Nightlife looks at where this technology is heading and what it could mean for all of us. 

Peter Marks, software developer and technology commentator from Access Informatics, joined Philip Clark and listeners to Nightlife with the latest tech news and information. You can listen here.

Some terrific club events

I've been a bit quiet here on the blog recently, in part due to some excellent club events I've been involved with.

The Macedon Ranges Amateur Radio Club had a great meeting with two fascinating talks.

Beekeeping Meets Radio: Building a LoRa Network for the Apiary

Bouncing Light Off Clouds: 357 km Across Bass Strait on 730 nm

The Radio Amateurs Old Timers Club had:

Melbourne ATV Repeater VK3RTV A Brief History – the journey from Analogue AM to High Definition Television by Peter Cossins, VK3BFG.

We are lucky to have so many excellent speakers and events here in Victoria, Australia.

My longest distance FreeDV RADEV1 contact 14,342km

There have been reports recently of 20m openings so I left WSPR receiving and noticed the US was coming in. Switched over to FreeDV RADEV1 using my macOS version of the software called FreeDVNeo. Keyed down and on Reporter I could see that Dudley WA5QPZ in Austin Texas was receiving me. Not perfect copy, but not bad either.

Also, I'm running the release candidate of macOS 27 Golden Gate which will be out in a few days. So far it seems stable and fast.