Radio Old Timers Club AGM

The Radio Old Timers Club annual general meeting and lunch was well attended by members of MRARC. Peter VK3RV, Jen VK3WQ, Ray VK3ACR and Peter VK3TPM attended. Old friends Nigel VK3DZ and Peter VK3YPG were also there. 

First the meeting kicked off with the annual general meeting which was conducted efficiently by Jim Gordon VK3ZKK with some members on Zoom.

Next a hearty lunch was served.

Mick VK3CH gave a detailed presentation about microwave operation.

Lots of gear was on hand but unfortunately wasn't turned on.

Don VK3BIG brought along what must surely be a new disruptive technology that could spell the end of FM radio - an AM stereo receiver.

Wonders will never cease! Nigel, VK3DZ is clearly boggled by this advancement.

50 Years of G-QRP Book review

Australian QRP and home brew enthusiasts typically subscribe to two fine newsletters, the local Lo-Key from the VKQRP club and the British SPRAT from the G-QRP club. Both are A5 format newsletters packed full of interesting projects and ideas. They are of sufficient quality to stand many re-readings over the years but it’s sometimes hard to find an item that comes to mind in the pile.

Lo-Key has an index and SPRAT sells back issues on CD or USB key.

When I heard of the publication of a book to celebrate 50 years of SPRAT, I didn’t hesitate to order a copy.

The G-QRP club was founded in 1974 by Reverend George Dobbs G3RJV (SK) who commented that there might be a demand for a newsletter “if there’s enough interest”. It turns out that there is.

Ed Durrant, G8GLM, has put together a fascinating selection of articles drawn from SPRAT over time. They are clearly marked with the year of publication and show the progression of technology available to the hobbyist over the 50 years. Beginning with low valve count gear and ending with SDR technology.

The book’s selection of projects is broken down into Transmitters, Receivers, Transceivers, Antenna systems, Test equipment, and Miscellaneous topics.

Although widely available components have changed over the years there is lots of great ideas within the collection that are still relevant today. There are charming mentions of the help that writers have received from other home brewing QRP operators. 

Many of the articles mention familiar names from other writing including Doug Hendricks KI6DS, Pete N6QW, Charlie ZL2CTM, Eric ZL2BMI, Roger G3XBM, and Wes Hayward W7ZOI. There’s a good number of VKs mentioned. I haven’t spotted VK3YE, but he’s probably there somewhere.

A few of the articles are reproduced with low contrast – I guess they’ve been scanned. Early items are charmingly typeset on manual typewriters. For the 100th edition I’d like to see an index added.

The book is available via the RSGB shop for £17.99 and less for members.

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.