Tech news spot on ABC Radio

I appeared on ABC radio last night discussing the tech news with Philip Clark. "Google's new "pixel 9" phones were revealed last month, and this morning, Apple hit back with new products, including a new iPhone. Tech Guru Peter Marks, software developer and technology commentator from Access Informatics with Philip Clark on Nightlife and the latest news and issues in technology."

You can listen here.

High quality AM exciter using a diode ring mixer with DC offset

There is a very active AM net here on 7.125Mhz and quite a few of the stations come up with home brew transmitters. (There's also a few using IC-7300s which do sound good on AM).

Dave, VK3ASE, mentioned recently that a good way to generate high quality AM is by using a diode ring mixer (which would normally produce double sideband with suppressed carrier) but with a DC offset added to the audio input.

My build is being prototyped on a literal bread board:

In place of a 7.125 crystal I'm using an Arduino Nano that simply boots up and puts an Si5351 on 7.125. That signal is buffered with a 2N2222 before being fed into a TUF-1 mixer. (I did build my own diode ring mixer but it doesn't work as well as the pre-built ones). I buffer the output and then amplify it through a few DB139s.

Only a few watts out so far and I'm keenly aware that AM transmitters like to provide RF feedback.

The Arduino sketch is quite simple and has bits of code primarily from Paul VK3HN.

/*

Single frequency oscillator

Si5351

Based on code from Paul, VK3HN

https://github.com/prt459/Arduino_si5351_VFO_Controller_Keyer

Don't forget:

* Arduino Nano 328p

* Old bootloader

* 115200 baud

*/

const unsigned long int FREQ_DEFAULT = 7125000ULL;

const unsigned long int FREQ_CALIBRATION = 370ULL;

#include <si5351.h> // Etherkit Si3531 library Jason Mildrum, V2.1.4

// https://github.com/etherkit/Si5351Arduino

#include <Wire.h> // built in

// Global objects

Si5351 si5351; // I2C address defaults to x60 in the NT7S lib

unsigned long int gFrequency = FREQ_DEFAULT + FREQ_CALIBRATION;

void setup() {

Serial.begin(115200);

Wire.begin();

Serial.println("Starting");

setupOscillator();

delay(500);

si5351.set_freq(gFrequency * SI5351_FREQ_MULT, SI5351_CLK0);

si5351.output_enable(SI5351_CLK0, 1);

Serial.println("Output enabled");

}

void loop() {

}

void setupOscillator() {

bool i2c_found = si5351.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0);

Serial.print("si5351: ");

Serial.println(i2c_found ? "Found" : "Missing");

si5351.set_correction(135000, SI5351_PLL_INPUT_XO); // Library update 26/4/2020: requires destination register address ... si5351.set_correction(19100, SI5351_PLL_INPUT_XO);

si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);

si5351.set_freq(500000000ULL, SI5351_CLK0);

si5351.drive_strength(SI5351_CLK0, SI5351_DRIVE_4MA);

si5351.output_enable(SI5351_CLK0, 1); // turn VFO on

printSi5351Status();

}

/*

The nominal status for each of those flags is a 0. When the program indicates 1,

there may be a reference clock problem, tuning problem, or some kind of other issue.

(Note that it may take the Si5351 a bit of time to return the proper status flags,

so in program initialization issue update_status() and then give the Si5351 a

few hundred milliseconds to initialize before querying the status flags again.)

*/

void printSi5351Status(){

si5351.update_status();

delay(500);

Serial.print("SYS_INIT: ");

Serial.print(si5351.dev_status.SYS_INIT);

Serial.print(" LOL_A: ");

Serial.print(si5351.dev_status.LOL_A);

Serial.print(" LOL_B: ");

Serial.print(si5351.dev_status.LOL_B);

Serial.print(" LOS: ");

Serial.print(si5351.dev_status.LOS);

Serial.print(" REVID: ");

Serial.println(si5351.dev_status.REVID);

}

Tim Bowden has died

ABC Radio legend and beloved presenter of ABC TV's BackChat program, Tim Bowden has died. He was a wonderful broadcaster, producer, writer and man.

Here he is with his wife Ros (who died a while ago).

We became friends when I was working for the ABC in Sydney. Mostly around Apple technical topics.

I vividly remember listening to his radio series Taim Bilong Master about the Australian involvement with Papua New Guinea. I own several of his books including Changi Photographer.

Here he is perched in the back of my van on the way to lunch a few years ago.

He has requested that there not be a funeral but I'm sure we can look forward to some well deserved tributes.

Contestia - faster, not better

Looking at digital modes for talking with people with high local receive noise I noticed Contestia in Fldigi. It's derived from Olivia but has a smaller character set. It only sends upper case letters. 

Stephen, VK2BLQ, has fairly high local noise. He's about 700km from me. To check if we have a suitable path for a QSO we both ran WSPR on 40m. He received my 2W at +3dB SNR so we switched to Contestia.

I received him perfectly but he wasn't copying me. It turned out Fldigi defaults to having the squelch turned on. Turning that off and he was able to copy me running down to 5W and probably lower.

My, incorrect, assumption was that Contestia used the extra bits compared to Olivia for better error correction. 

Reading from the Fldigi documentation page on Contestia.

"Contestia is a digital mode directly derived from Olivia that is not quite as robust - but more of a compromise between speed and performance. It was developed by Nick Fedoseev, UT2UZ, in 2005. It sounds almost identical to Olivia, can be configured in as many ways, but has essentially twice the speed.

… 

Contestia performs very well under weak signal conditions. It handles QRM, QRN, and QSB very well also. It decodes below the noise level but Olivia still outperforms it in this area by about 1.5 - 3db depending on configuration.”

It seems the objective was faster typing speed which I don’t really think is important.

So… thanks for the experiment but I think we should use Olivia in future.

Now, looking at the Olivia page in Fldigi.

The first tip they give is to turn off (or down as much as possible) the squelch.

There’s a bit of talk about different sub-modes but it seems to be about getting faster speed. They say if you’re on 250/8 and want faster (in good signal conditions) go to 500/8. 

My question is "what is the best keyboard to keyboard chat mode for low signal to noise radio channels?".

Gear for a remote radio guest - Mix minus

Regular readers will know that I'm one of those commentators you hear on the radio. I've always been keen to have my audio sound as close to the studio as possible and I think I'm getting close.

Without a noise dampened studio I need to get close to the microphone to avoid reverberation but I have a tendency to "pop" the mic so I need to monitor my local audio as well as hearing the host. We used to call this "mix minus" where the guest hears a mix of the other speakers and themselves but just the guest's mic would be sent back to the main studio. I've been hunting for how to do this on a computer.

Richard, VK3LRJ, had just the device I needed. It's a Behringer Xenyx 302USB. These aren't new but have the ability to let me hear the mix while sending just the mic up the line. It's also a USB sound card so plugs in to the computer and is powered from that USB port.

One interesting note is that it says the XLR mic socket has phantom power but my Rode mic didn't work. Turns out the phantom power is about 14V rather than the 48V norm so some microphones work but others don't. I'm using a Sure dynamic mic, similar to the studio. These mics have quite low output but this mixer has enough gain.

Anyhow, here's the latest appearance:

Telegram is just one of many messaging apps, being targeted in France over secure messaging, but just how secure is it? AI is the biggest development in technology, and it seems it's also the job that pays the best. Plus, growth in the PC and Phone markets has been slowing, and the next big thing that may stimulate people to upgrade their PC and phone is new AI features that the old models don't offer. Tech Guru Peter Marks, software developer and technology commentator from Access Informatics, with Philip Clark on Nightlife and the latest news and issues in technology. 

You can listen here.

Tech news spot on ABC Radio

A new ID system for Australians. At a speech at the National Press Club today, Government Services Minister Bill Shorten announced the trial of a new way for us to identify ourselves that is more secure than things like our driver's license but will require a phone. Also, have you ever got to the checkout to find that the price is different to what it was on the shelf? Have you ever looked at a price online again and found it has changed? These are examples of "dynamic pricing". Plus, in recent years, particularly in rural Australia, a new internet provider has quietly been gaining market share and now they've grown significant enough to attract the attention of the ACCC. How big of a provider is Starlink today? 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.   Listen here.

As an aside, I'm pretty happy now that my audio quality matches the studio quite well despite me joining the program from my home office.

ePaper solar power monitor with Lilygo T5

The house here has 6KW of solar power, when the sun is shining and hitting the panels. I like to watch what's being generated so I can use power from the sun if available so some time ago I reverse engineered the Envoy inverter's web display and made some M5 Stack devices that display the info. They have an ESP-32 for Wifi built in. 

Sometimes the sun also shines on the LCD making it hard to see so I've just ported my code to a Lilygo T5-2.13 E-Paper board also with an ESP32.

E-paper is highly visible although refreshing is a bit slow and ugly. The Arduino compatible libraries are available here. Things didn't quite compile as given but I was able to work through it.

The E-Paper board uses negligible power when sleeping, and the display remains visible, so these could be run from a small battery if desired.

Building a quadcopter drone from parts

It's been many years since I've built a quadcopter from parts. What triggered this project was stumbling across the SpeedyBee flight controllers which have a powerful STM32 F405 and bluetooth so they can be configured wirelessly from a smartphone app. The controller has the motor controller (ESC) board mounted under it which makes for a much neater arrangement than the last time I did this which involved have ESCs on each arm of the drone.

Here's a closeup of the flight controller with ESC board under it.

The SpeedyBee uses a version of Betaflight. It arrived with the latest version. I've added a GPS module and was hoping to get a GPS Hold mode but that doesn't seem to be available in Betaflight. There are comments that even if it were available it doesn't work very well due to the poor accuracy of GPS position.

Here's my list of parts:

Frame

FPVDrone 5 inch frame Mark4 225mm FPV Racing Drone Frame Carbon Fiber 5inch Quadcopter Freestyle Frame Kit with Lipo Battery Strap $79.67 Amazon

https://www.amazon.com.au/dp/B082SPT5D9

Receiver

FLYSKY FS-A8S V2 2.4G 8CH Mini Receiver PPM I-BUS SBUS Output for Flysky FS-i6 FS-i6S Airplane FPV Racing Drone Transmitter

https://www.aliexpress.com/item/1005005699957173.html $12.87

Transmitter

Flysky FS-i6X 10CH 2.4GHz AFHDS 2A $$57.01

Buzzer

5V buzzer $2

https://www.aliexpress.com/item/32996116481.html

Motors 2300KV

RS2205 2205 2300KV CW CCW Brushless Motor for FPV RC QAV250 X210 Racing Drone Multicopter $24.78

GPS

GPS BN220 $12.26

https://www.aliexpress.com/item/1005006319024804.html

Flight controller and ESC

SpeedyBee F405 V3 30x30 Flight controller + 50A BLS 4 in 1 ESC

$109.88

https://www.aliexpress.com/item/1005005486457877.html

Flight controller:

https://www.speedybee.com/speedybee-f405-v3-bls-50a-30x30-fc-esc-stack/

5-inch propellers

5x4x3 5040 three blade ebay.

I already had a transmitter but it's rather bashed up and getting unreliable. I also have batteries in stock.

All up about AU$250.

Once I got the propellors turning the right way and enabled Horizon mode it flys quite well. Next step is to add a camera and transmitter. This will be a good "knockabout" drone for hoisting antennas and other such activities.

Betaflight?

I was surprised to see that the SpeedyBee flight controller runs Betaflight as when I last played with this stuff the Cleanflight fork was the leading software. It turns out the modern Betaflight is now a fork of Cleanflight and is the most popular and up to date. This is explained on the excellent documentation wiki.