Soldersmoke DC Receiver - excellent build-a-thon on Discord

Discord is a kind of chat board where a group of people can create topic channels and basically talk back and forth in real time - if they wish.

Bill and Dean at Soldersmoke have embraced the form and created a fantastic place where many of us are sharing our issues, if they arise, and helping each other to debug things. The "smokers" are both there but also there's a good deal of constructors helping each other out.

My receiver has been re-built a few times and currently looks like this:

Bill urges us to stick to the design but some of us have had to substitute components or, in my case, due to the lack of an audio transformer that works, add a bit of extra audio gain in the form of an LM386 module.

Several builders have found that we get less output from the VFO than Bill or Dean do and the tell-tale squared off waveform at the input to the diode ring mixer isn't there. It's hard to know what the root cause is but presumably it's component variations or perhaps the "brass" screw material, which, in my case quenches oscillator level as it goes in to the coil. (Adding a 0.1uF cap across the resistor in the source of the buffer FET helps).

The Discord is broken out into channels for the oscillator, mixer, bandpass filter and audio amplifier.

You can join via this link (which will expire in a week). After that check out the Soldersmoke blog for new info.

Congratulations to Bill and Dean for this innovation.

My receiver is working quite well, thanks in particular to VK3ZZC who gave me some NP0 capacitors that have stopped the massive thermal drift in the VFO. It is very satisfying tuning 40m listening to stations - sounding really good - on a home made receiver.

If you are new to home brew radio construction, this is a good way to get started with a community of helpful people. 

Tech Talk on ABC Radio

Nightlife Tech Guru Peter Marks, a software developer and technology commentator from Access Informatics, joined Philip Clark on Nightlife to discuss the latest news in technology. This week: China’s new AI chatbot tool, Deep Seek has launched and its capabilities have shocked the technology sector and it rocketed to the top of app stores around the world. Has American pre-eminence in artificial intelligence been obliterated? 

https://www.abc.net.au/listen/programs/nightlife/tech-talk-with-peter-marks/104869386 

Cheap Yellow Display (CYD) board

In the past I've used some of the ESP32 boards with a small OLED display on them. It's very handy having the display already there. Recently I saw mention of a "Cheap Yellow Display" (CYD) board with a large colour LCD for AU$20. 

It's a very capable board with extra GPIO available.

My first project was to build an NTP synchronised clock:

It's a resistive touch screen but I'm not sure I'll use that feature.

There's a GitHub repo with helpful software. You do need to grab the User_setup.h file from here and put it in the LCD library directory to get things to work.

A bit of FreeDV's new RADEV1 mode heard on 40m

Tuning around on 40m today just after noon I heard a digital mode and soon figured out that it was a FreeDV contact between two VK5 (South Australian) stations. I'm in VK3 so they're about 600km away.

A great thing about digital voice is the lack of band or interference noise. You can see quite dramatic selective fading but the speech is perfectly readable.

FreeDV is under active development and the new RADE mode is a big step up on past modes. It's wonderful to see quite a lot of activity at times but we have a long way to go. You can see who's on at https://qso.freedv.org/ which is also visible in the GUI app.

Here's a capture from over the weekend:

You need version 2.X to get the new RADE mode. It's available built for Windows and macOS on the releases page. 

If you're on Linux, including Ubuntu and Redhat, there is a build script by Barry Jackson which downloads all the dependencies and does the build with hardly any intervention. 

Soldersmoke Direct Conversion Challenge - revisited

I built the direct conversion receiver described on the Soldersmoke blog a while back but ran in to several problems. The audio chain was very unstable and, perhaps ironically, the audio output level was very low.

Hackaday has also been covering this receiver project.

After some very enlightening discussion on the latest podcast I went back and re-built the audio amplifier chain. 

One insight was that the gain of the three stages depends on the gain of the transistors and testing mine I get hfe of 350 which is up at the top of the range and might have helped with instability. The other insight was that there are bad 1K:8R audio transformers around and I suspect mine is causing low output audio.

Finally, I was unsure about how much drive a diode ring mixer needs. On the podcast they mentioned +7dBm which should be measured into a 50 ohm resistor and not into the mixer. I hadn't done that before. My VFO put 0.8V into 50 ohms which I calculate to be about +2dBm so too low.

Adding a 0.1uF capacitor in parallel with the resistor in the FET's source raised output a bit and I'm now getting the desired squared off waveform at the input to the mixer. I have struggled to get enough drive out of the oscillator and have tried a variety of tricks including adding extra gain stages.

I've just had a tune around 40m and can hear stations from all up the east coast quite well. Distances over 1,000km. (Although the lack of AGC means my ears hurt sometimes).

VFO tuning is very sensitive but I know things can be done about that. Actually, I love this VFO with the PTO tuning.

Note that while I have built the band pass filter I don't find it is needed at my home so I've left it out for now.

Thanks again to Bill, Dean, Pete and Hackaday for the prompt to have another go at this amazing home brew project.

Update: NP0 Capacitors and now it is very stable

My PTO drifted badly with ceramic capacitors. I went looking for NP0 caps and found a little bag given to me by Ralph VK3ZZC at some point. These have made all the difference as you can see from this video.

Tuning is very sensitive but when I stop touching it all is very stable.

For reasons I can't understand my VFO puts out less power to the mixer than Bill's so I've added an amplifier stage which has done the trick.

Tech talk on ABC Radio

Nightlife Tech Guru Peter Marks, a software developer and technology commentator from Access Informatics, joined Philip Clark on Nightlife to discuss the latest news in technology. This week: the annual Consumer Electronics show has just wrapped up with all sorts of amazing new gadgets they want us to buy, a fridge that will end the need for door magnets, a vacuum cleaner that tidies up, and new TVs with AI.  

You can listen here: https://www.abc.net.au/listen/programs/nightlife/tech-talk-with-peter-marks/104817498

Visited Australia's first computer CSIRAC with VK3ZZC

There's a terrific series of videos covering Australia's history in computing I noted in this post. After watching the episode on CSIRAC, I demanded that Ralph, VK3ZZC, join me in a visit to Spotswood to see it. (Click to enlarge).

The display is not well lit I'm afraid but Ralph was able to point out the features of it to me.

"Physicist and mathematician Trevor Pearcey and electrical/mechanical engineer Maston Beard led the design team for this computer, the first in Australia, and it was built by the CSIRO Division of Radiophysics. CSIRAC demonstrates how Australian designers, working largely in isolation, could successfully build one of the world's first computers. SIRAC ran its first program in 1949 and operated until 1964, performing computations for scientific, engineering and commercial projects.

It is now the only intact first generation computer."

The pumping station is also a wonderful thing to see.

Some images deserve to be black & white.

Also there is restoration work being done on the Melbourne Telescope in a wonderful workshop that I plan to use as a videoconference background in future.

ScienceWorks is a good thing to visit although it seems targeted at toddlers. I thought it would be difficult to get to but it's walking distance from Spotswood station which is very well connected.

Built a switched inductor L match antenna tuner

Peter, VK3YE, has a very neat portable setup that includes a nicely beaten up FT817 and a pocket sized L-Match antenna tuner that seems to work very well for him. He described it on his site and in a video and there are many descriptions of this simple circuit. I built one for QRP use in a small plastic box.

My version allows the capacitance to be switched between the input and output. (Click to enlarge).

So far I've tested with a MiniVNA plugged in to my (currently half down) off centre fed dipole and it certainly changes the reactance wildly when adjusted.

What are all those squiggly lines on the 10m band?

The 10m, 28MHz, band seems rather lively today. I have just a low height wire dipole and am using an AirSpy HF+ but just look at all the visible activity:

(Click to enlarge).

I've often wondered what all those squiggly lines are. They usually, but not always, start and then sweep up in frequency. People have said either that they're high energy particles hitting the upper atmosphere or that they are distant welding machines that can be heard because of good propagation conditions.

It's wonderful to be able to see large parts of the spectrum like this.

Bulk convert MOBI to ePub (or other eBook formats)

I've just switched from a Kindle to a Kobo book reader. I have a collection of old MOBI format books that I wanted to bring over the the Kobo. It does read MOBI books but I see some weird erros like this:

I've found that converting to ePub in Calibre avoids these problems but I have a folder full of files to convert. Calibre has a command line tool called ebook-convert that can convert a file and seems to work well. Based on past work by others I've created this script to convert a directory of ebooks over to ePub in a directory named "converted".

#!/bin/bash

# bulk-convert

# based on https://github.com/captaincouch/lame-bulk-convert

# Set the $SAVEIFS variable as the global Internal Field Separator character.

# This preserves the original global $IFS variable to change it back later.

SAVEIFS=$IFS

# Set the $IFS variable to a space character using substitution escape sequence 

# for the space character.

IFS=$(echo -en "\n\b")

# Create a new directory for the newly-converted files, if not already existing.

mkdir -p ./converted

# Loop and convert each file "i" to mp3. Quotation marks are used to account for

# spaces and illegal characters. The files are placed in ./converted-mp3/filename.mp3.

for i in $(ls)

do

# Set a variable "c" containing the filename with the ".ext" extension removed.

# For example, "sound.wav" would become "sound", and "sound.foo.wav" would

# become "sound.foo".

c="${i%.*}"

ebook-convert "$i" "./converted/$c.epub"

done

# Set the $IFS variable back to previous value, using the value stored in $SAVEIFS

# for safekeeping.

IFS=$SAVEIFS

Switched from Kindle to Kobo ebook reader to borrow from the Library

I love reading books on a small eInk reader. A friend recently lent me a printed book (War by Bob Woodward) and I was enjoying reading it but not enjoying carrying it around so I purchased the book from the Kindle store.

My local library in Kyneton is part of the Goldfields Library Corporation and they have agreements with several eBook lending systems including BorrowBox and Libby. The Kindle does not support eBook borrowing - they want you to buy from their store. 

Another thing the Kindle doesn't support is the Pocket read it later service. (There is some sort of workaround that uses the email to Kindle service).

I've purchased a Kobo Clara BW. (I have little interest in a lower contrast colour eInk device).

The Kobo is a bit smaller than the Kindle I have and the screen is set in from the face unlike the Kindle. It charges and connects with USB-C. Setup was quite easy, I gave it the Wifi credentials and it did a software update.

The first thing I tried was plugging it in to my Mac. It mounts as a disk. I copied over an old MOBI format book and it appeared in the library. MOBI is an old Kindle format that they still support but don't recommend. (I think the DRM has been well and truly cracked). Kobo supports a range of formats natively including ePub, PDF, FlePub, TXT, HTML, RTF and also MOBI.

The MOBI file I copied over works well enough on the Kobo but I noticed some visible formatting incantations in the text. Perhaps their MOBI implementation isn't complete?

I favour ePub and while you can put them on a Kindle you must email them to get them converted.

eBooks from the Library

Setting up the Kobo to be able to browse and download loan eBooks from my library account was a bit of a puzzle. I went to the Discover tab and selected OverDrive (which is the way one accesses BorrowBox). It asked me to add my library. I tried Kyneton without luck, next I tried Goldfields. Finally I found a library in Ballarat and, guessing that it might be in the Goldfields group, chose that. Next I entered my library card number and PIN and it worked!

I am able to scroll through or search for books they have available. They do make it look like you need to purchase the book but tapping the three dot button shows an option to "Borrow with OverDrive". I sucessfully borrowed a book which quickly downloaded. It expires in 14 days.

The option to borrow rather than buy is well hidden. Dark pattern there from someone...

Pocket

Pocket is a service from the FireFox folks where you click a button in your web browser while viewing a story you want to read later and it magically gets cleaned up and sent to your reader. On the Kobo, this is in the More tab and they call it "My Articles" (although the pocket logo is easily recognised.

I had a bit of trouble getting the autentication to work and the Kobo said at one point they were having trouble too and are working on it. I tried again and it went through.

After sending an article to Pocket on my desktop computer I found that I need to tell Pocket on the Kobo to "refresh" (in the ... menu) in order to get what's new. I do like the fact that Pocket documents are separate to books rather than being mingled as they were on the Kindle.

Borrowing eBooks from a library is rediculously confusing. Things have different names, authentication seems unreliable, and I doubt that normal library users would figure it out. Perhaps Libraries are not motivated to make it easy?

Conclusion

So far I like the Kobo. I notice a bug where it seems to think I'm just 1% through books in the main listing even though I'm much more than that. Long tap to show the dictionary definition of a word doesn't work with MOBI books so perhaps that's also why the MOBI book I'm reading doesn't show progress.