Tuesday, October 12, 2021

On ABC RN's Download This Show

This week I'm a guest on Marc Fennell's ABC RN "Download This Show".

"We’ll soon be walking around with them and flashing them to wine, dine and travel – but how easy will it be to spot a legitimate vaccine passport compared to a fake one? We discuss what could have prevented a security flaw and what’s being done about fake vaccine passports.  

Meanwhile, the Commonwealth Bank of Australia will be using an artificial intelligence tool to stem abusive messages being sent on electronic payments.

Plus, Facebook and Instagram introduce new features in an effort to protect young users from harmful content.

And would you wear a smart headband that claims to make you calmer?"

Marc was in the studio, I'm at home using an Audio-Technica USB microphone and I think it sounds as good as the studio.

uSDX tiny multi-band transceiver

The uSDX is not a great receiver or transmitter but it is usable and amazingly small. I bought mine through AliExpress. "uSDR uSDX 10/15/17/20/30/40/60/80m 8 Band SDR All Mode HF SSB QRP Transceiver Compatible with uSDX QCX-SSB".

Here's a recording of how a fairly week signal on 40m sounds:

The first unit I bought arrived with a broken screen. The AliExpress vendor provided free shipping for the return and refunded my payment.

I previously built the same circuit but this fully built version is more compact.

Manuel, DL2MAN who is the original designer of the uSDX sandwich contacted me with some comments about this (and similar) clone of his design. He has a video commentary and makes the following points:

  • His design is used but there is no credit to him at all
  • The license on the design was for non-commercial use only
  • He was never asked about a commercial license
  • The selling price is way above the actual cost (he thinks it would cost about US$40-$50) particularly as they are not supporting the developer
  • No effort was made with documentation, they've added no value for their margin
  • There are some changes to the schematic:
    • Output transistors have been changed but other parts of the circuit have not been adjusted
    • Harmonic suppression will be worse than the original design (and way below legal requirements)
    • Firmware upgrading is not easy as it was in the original design
    • The battery charging circuit is noisy
  • A physical design problem can short circuit the battery in the version with a battery
DL2MAN has now changed the license to Creative Commons but, of course, to comply manufacturers need to mention the source and re-publish their version under the same license.

So, all the materials are now available for legal manufacturing.

Manuel is clearly angry about the way he has been treated by the Chinese manufacturers who have stolen his work, without attribution and are profiting from it. There is an update of the design and Manuel feels it could be made for about $50 soon.

There's a video here that compares Manuel's latest version with one of the Chinese clones.

Friday, October 01, 2021

It's a good idea to update the Arduino IDE

There's some tribal knowledge around about Arduino IDE (and library) versions. I've heard from people that a certain version is the one that works and they don't want to update. Partly this is because they are using an old library and new code "breaks" the build.

Recently, I was talking with Paul, VK3HN, and he mentioned that he had a sketch that, when built for an Uno, was short of RAM.

Paul sent me the code, I compiled it, and didn't get the warning.

This was puzzling of course. I figured it could be one of two things:

  • One of the libraries had been improved to use less RAM
  • The gcc compiler bundled in the IDE had improved.
Here's the compile output from Paul:


Here's my output:


The figure is dynamic memory use:

Paul: 1539
Mine: 1132

Quite a big difference if you only have 2048 bytes of RAM.

It turned out that I was on a slightly later version of the IDE 1.8.15 (not even the latest) and Paul was on 1.8.12.

I tried the beta of Arduino IDE 2 and got the same memory use so I think the version of gcc bundled in it is the same. 

gcc has lots of options and, while I understand the Arduino IDE wants to keep thinks simple, it would be good if the compile options were exposed.

The lesson out of this is that the tools do get better and it's a good idea to upgrade.

Wednesday, September 29, 2021

Dallas, VK3EB's HF bush antenna

Dallas, like many of us, doesn't have much scope for a decent HF antenna at home so he has perfected the art of putting up antennas in trees. Check this out:


Excellent work!

Here's a previous video where I visited and you can hear some of the low noise reception available:



Tuesday, September 28, 2021

Facebook fake account scam promising "Mega Bonus"

This morning a friend said hello on Facebook messenger. The message said that we hadn't talked before - which was believable as we normally use other modes. I accepted the message and we were away:

"doing pretty good" was a red flag right away. "help the Old, Retired, Disable, " was another indicator. Why can't these people get basic grammar right? Or is it deliberate? I asked for more.


Of course I won't be making contact and I wonder what the next steps would be. Presumably this is a 419 scam where some fees need to be paid to clear the way for the $150,000 (which will never arrive).

Meanwhile, I viewed the account page and could see a fake Facebook account with Richard's profile picture on it and no other content.


I was really hoping the scammer would answer my video call but no such luck.

This happened to me a decade ago and I know Facebook has a mechanism to report fake accounts. You go to the profile page, click the "..." under the profile picture and choose "Find support or report profile". There is an item there for fake accounts.


The instant I reported the account I started getting "query error" on it so I suspect others had also reported it. Facebook did act quickly in this case.

To create the fake page they must have been able to see Richard's page and copy his profile image. The scammers must be able to see his friends list too - which is concerning.

I looked at my privacy settings but they seem to change frequently and I'm really not sure if I'm still vulnerable. There should be one big switch that defaults to private but there's not.

The Facebook platform seems to be a major location for scams including all the posts designed to go viral that gather engaged users or capture information that could be used for identity theft.

Tuesday, September 21, 2021

Resistive tap built with sharpie PCB etch

I'm keen not to burn out the input to the spectrum analyser. It's 50 ohms in with a maximum of +30dBm. The solution is to transmit into a dummy load and sample the signal with a resistive tap.

A good candidate for a simple PCB and I used Paul Taylor, VK3HN's, technique of drawing resist on the board with a sharpie. Components are all soldered on to the top of the board so laying them out to figure out where the tracks go is easy.

Here's the circuit and the components for the board:


I cleaned the board to remove fingerprints with Isopropyl Alcohol - is that the best thing to use? Using components to lay out the board, tracks were drawn with a standard sharpie. I didn't go to much trouble and could probably have filled in more of the board with earth plane to minimise the amount of copper to be etched.


In to a small bath of Ferric Chloride. While gently rocking we had a magnitude 6 earthquake which was fun. It took about 20 minutes to clear the copper.


After washing under water the etch looks great.


Steel wool was used to rub off the sharpie ink. 


Here's the completed board. 


I've got some more of the nice board edge mounting SMA sockets coming so had to make do with a panel mount for the tap output.

What should I use to protect the copper? I think Paul just tins the whole board but maybe there's a spray lacquer that would still allow solder modifications but prevent oxidation.

Sunday, September 12, 2021

An OWON XSA815-TG Spectrum Analyser for the bench

I've wanted to try a spectrum analyser for many years but they've been prohibitively expensive. Just as oscilloscopes have come down in price, spectrum analysers are also getting cheaper. I bought an OWON XSA815-TG Spectrum Analyser from Banggood for just under US$1,000.

This one is good to 1.5GHz which should be plenty for my use.

So far, I'm really impressed. It's very easy to use - easier than many CROs. Certainly easier than the TinySA. Here it is showing the local FM broadcast band:


Here is a signal from a 2m FM hand held (received off air):


Here is the tracking generator in operation showing a 9MHz low pass filter:

There is lots to learn but I feel that after a CRO, a spectrum analyser is a wonderful piece of test equipment that is now within financial range of some of us lucky hobbyists.

The terrible interference I often see on 40m has just returned. Here's how it looks on the IC-7300:


I tried plugging the antenna into the spectrum analyser in the hope of seeing the overall noise but I'm not:


I think I need to play with attenuation and gain to see what's going on. Much to learn!

Here's the output of my recent Si5351 WSPR transmitter with a fairly poor low pass filter after it. Those second and particularly third harmonics look pretty big.



Tuesday, September 07, 2021

Simple WSPR Beacon using Si5351 and ESP8266 NTP for time sync

Wanting to play with a simple WSPR Beacon in the house where I can't receive GPS for time synchronisation, I've hacked together a beacon using an Si5351 oscillator and an ESP8266 board that joins my Wifi and gets the time from an NTP server.

Here's the rig:


It starts off by joining Wifi, then requests the time from time.nist.gov. Next it figures out how many seconds to wait before the next 2 minute slot and delays that long. The WSPR signal is transmitted followed by a 10 second delay before requesting the time again. Assuming the NTP server replies, WSPR transmission is every second 2 minute slot.

The Si5351 generates a square wave into 5cm of wire and there's massive hum on the signal presumably due to the USB power. Here's how it looks decoding off air:

I got this going using a WeMos D1 R2 board which is basically an ESP8266 on an Arduino style board. I tried to use an ESP32 but for some reason (possibly power voltage) I couldn't get it to talk to the Si5351 although it could see it on the I2C bus.

Just a toy really but might be useful for something. The source code is here.

I'm using Arduino 1.8.15 and the following libraries are installed:

  • Etherkit JTEncode 1.3.1
  • Adafruit Si5351 1.2.1
  • Other libraries for UDP were bundled with the board, in my case LOLIN(WeMos) D1 R1