Dremel cut PCB construction

Prototyping small circuits where it's not worth designing and etching a board can be done in many ways. I've used "ugly" (which I think is rather beautiful) where components float above the copper ground plane; MePads where small copper pads are superglued to the base plane; or strip board with track cuts.

Recently I've converged on a system that's working quite well for me.

The circuit is drawn out in pencil and the outline of the PCB rectangle is traced.

Working through what should not be connected to what, I draw the cut lines under a spaced out version of the circuit. Here's my drawing and below the final working board.

I mark up the board with the planned cuts.

To make the cuts in the copper, I lay the Dremel with a cutting wheel on the bench and lean it so that it just cuts the copper. I draw the board along the wheel, leaving the Dremel stationary. I can get pleasingly straight cuts this way. It is worth checking for non-conduction between areas with a multi-meter as sometimes a strand of copper can be left at a corner.

To hold components against the board for soldering you need some sort of "helping hands" but the one I learned about from an Adam Savage video is called Omnifixo. They are not cheap but are well worth it for all the cleverness.

For years I've been using a little, rather low power, bench soldering iron but I find that quite a lot of power is needed when soldering to large copper areas. I have switched to a 70W iron and it is a revelation.

Naturally, I first had the transistor in the wrong way around, but after that was fixed. The joy of oscillation was experienced.

I'm sure this is not news to any readers but I thought it worth documenting for some who might be getting started with home construction. It's not as compact as other techniques but lends itself to making changes.

One other thing I do these days is add an LED (and resistor) to the power line. It looks nice and I can't tell you how much time I've wasted wondering why an un-powered circuit doesn't work!

Experimenting with an SSM2167 compressor limiter board

The home brew AM transmitter on the bench at the moment has thrown up the issue of either low or over modulation from my mic audio. Some time ago, I purchased a couple of interesting boards described as "SSM2167 Preamp Compressor Limiter Noise Gate Dynamics Processing Module DC 3V-5V Microphone Preamplifier". They are under AU$5 from AliExpress and really tiny.

To aid with experimentation, I've mounted mine on a carrier board.

R1 on the board controls the noise gate, which I'm not too interested in. R2 controls compression and came with a 1k resistor in place. The data sheet has this table:

1k would give almost no compression. A strange choice given how the boards are marketed. Happily there are big through holes available on the board for both resistors.

With the un-modified board I fed a 1kHz tone in and get peak to peak voltages:

50mV -> 440mV

100mV -> 880mV

200mV -> 1.43V

Higher inputs do not give higher output. The output waveform looks pretty good, so not clipping. Gain is rather low for my dynamic mic however.

I replaced R2 with a 100k resistor and it has much more gain.

5mV -> 880mV

10mV -> 960mV

20mV -> 1.06V

Output level stops there and again gain is being reduced.

Stephen, VK2BLQ, brought this idea to my attention as it has been discussed as helping the uBitx radios.

First contact with home brew AM transmitter on 7.125

For too many weeks I've been tinkering with a small transmitter for the active AM frequency of 7.125Mhz and just now I called CQ and was kindly answered by Ross, VK3ARW. He reported good signal strength both where he is (west of Bendigo) and on the Ironstone ridge SDR in South Australia. The transmitter is home brew (although I used a Jaycar mic preamp kit).

I've been testing by listening to myself on the PKLoops SDR.

The transmitter uses an Arduino Nano that simply boots up and tells an Si5351 to put out 7.125MHz. There's an RF buffer using a 2N2222. The magic happens, the generation of AM, using a simple diode ring mixer that is set to be off balance. Mic audio, from the preamp, is fed in and out comes AM. (This technique was mentioned by Dave, VK3ASE, who also uses it). There's another 2N2222 gain stage then a low pass filter. Next I have the three stage RF power amp from Drew Diamond's 80m transmitter. Finally another low pass filter for 40m.

To answer Ross's question.. out of all this I get about 1.5W so, for the sake of getting some contacts I've fed this in to a little RF amp that gives about 25W peak.

I must say I'm astonished that I didn't get RF feedback or other instability given the construction. Despite Ross's kind words on the audio I can see that a peak limiter is needed to keep modulation up without over-modulating.

Python code to generate WSPR audio tones

Ross, EX0AA, is working to do WSPR on very low frequencies and asked for some help generating WSPR tones as audio directly. There are several projects around that generate WSPR via GPIO pins, Si5351s or an AD9851 DDS.

I grabbed the AD9851 code from PH0TRA, removed the DDS code, and with the help of ChatGPT, modified it to generate audio directly using pyaudio. This works both on my Mac and on a Raspberry Pi with no modification. The audio comes out of the default device, and if you plug in a USB audio dongle it comes out of there.

It seems to decode just fine with acoustic coupling.

My code is here. You'll also need genwsprcode.py modified by PH0TRA from code by the fabulous Mark VandeWettering K6HX.

You'll need to use Python 3 (of course) and install pyaudio and probably numpy.

Usage: python3 wsprgen.py CALLSIGN GRID dBPower BASE_AUDIO_FREQUENCY

Thanks Ross for the push to make this. It could be handy for others.

Installing on a raspberry Pi

Thanks for the prompt from AA7US asking how to get going on a raspberry pi.

• Grab my code from the GitHub gist. (you can download the file or copy and paste).
• Grab PH0TRA's code from here. Put it in the same directory.
• Install the needed python modules:
• sudo apt install python3-pyaudio
• sudo apt install python3-numpy
• In a terminal run the program like this:
• python3 wsprgen.py --no-delay CALLSIGN GRID4 DBM 1500

Obviously replace CALLSIGN GRID4 DBM. 1500 is the base audio output frequency in Hz.

--no-delay starts outputting right away, good for testing. Remove that to have it wait for the top of the 2 minute block. You'll get a bunch of output from the audio software but it seems to work after a few complaints. Here's my output:

python3 wsprgen.py --no-delay vk3tpm qf22 33 1500

symbols

 3,1,0,0,0,2,0,0,1,2,0,2,1,1,1,0,2,2,1,0,2,3,0,1,3,1,1,0,0,2,0,2,0,0,1,2,2,1,0,3,2,2,2,2,2,2,3,0,3,1,2,0,3,3,0,3,2,2,0,3,3,2,3,2,2,2,0,1,1,0,1,2,1,2,3,2,3,2,0,3,2,0,3,2,3,1,2,0,2,1,1,0,3,2,1,2,0,0,3,2,2,2,0,0,3,2,2,3,2,2,1,3,1,2,3,1,2,2,3,1,2,1,2,2,0,1,1,3,2,2,2,0,2,1,2,3,2,2,3,1,0,0,0,0,0,0,2,1,1,2,1,2,3,3,0,2,2,3,1,2,0,2

ALSA lib pcm_asym.c:105:(_snd_pcm_asym_open) capture slave is not defined

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.front.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM front

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround51.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround21

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround51.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround21

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround40.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround40

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround51.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround41

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround51.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround50

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround51.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround51

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.surround71.0:CARD=0'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM surround71

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM iec958

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM spdif

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.iec958.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM spdif

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

ALSA lib pcm_oss.c:397:(_snd_pcm_oss_open) Cannot open device /dev/dsp

ALSA lib pcm_oss.c:397:(_snd_pcm_oss_open) Cannot open device /dev/dsp

ALSA lib pcm_a52.c:1001:(_snd_pcm_a52_open) a52 is only for playback

ALSA lib confmisc.c:1369:(snd_func_refer) Unable to find definition 'cards.0.pcm.iec958.0:CARD=0,AES0=6,AES1=130,AES2=0,AES3=2'

ALSA lib conf.c:5180:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory

ALSA lib conf.c:5703:(snd_config_expand) Evaluate error: No such file or directory

ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM iec958:{AES0 0x6 AES1 0x82 AES2 0x0 AES3 0x2 CARD 0}

ALSA lib confmisc.c:160:(snd_config_get_card) Invalid field card

ALSA lib pcm_usb_stream.c:482:(_snd_pcm_usb_stream_open) Invalid card 'card'

ALSA lib confmisc.c:160:(snd_config_get_card) Invalid field card

ALSA lib pcm_usb_stream.c:482:(_snd_pcm_usb_stream_open) Invalid card 'card'

ALSA lib pcm_dmix.c:999:(snd_pcm_dmix_open) unable to open slave

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock

Waiting for next WSPR TX window...

Start of transmission on: 03:20:04

Frequency: 1,500 Hz

symbol = 3, out_frequency = 1504.39453125

symbol = 1, out_frequency = 1501.46484375

symbol = 0, out_frequency = 1500.0

symbol = 0, out_frequency = 1500.0

symbol = 0, out_frequency = 1500.0

symbol = 2, out_frequency = 1502.9296875

symbol = 0, out_frequency = 1500.0

You'll hear the tone on the default output. In my case I plugged in a USB audio dongle.

The Secret Life of the Radio

Thanks to Lindsay, VK3GX, for bringing this wonderful BBC program to my attention. The team shows the development of radio and makes various transmitters and receivers. They build a coherer and demonstrate it for example.

Keep watching after the end credits for some comments from the presenter.

Incidentally, the cartoon depiction of Marconi's home are quite accurate. I visited it some years ago.

Tech news spot on ABC Radio

How do you remember your passwords? Making up and remembering unique, complex passwords is a struggle for many of us. Those days are ending. What are PassKeys and how will they help? Plus, Modern cars have many "driver assist" features. Things like lane following and emergency braking. Car speed-warning devices are spreading, all cars sold after 2030 in California will be equipped with either GPS or a front-facing camera that will give warnings if a driver is travelling more than 10 miles over the limit. Tech Guru Peter Marks, software developer and technology commentator from Access Informatics with Philip Clark on Nightlife with all the latest news and issues in technology. 

You can listen here.

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.

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.

QRP operation from a motel room

This year I fulfilled a long term ambition of visiting Uluru in the centre of Australia and I couldn’t help thinking how spots from there might look on a WSPR map. Here's a spoiler (plotted in WSPR Watch):

Operating QRP from a motel room is a challenge in several respects. From past experience I knew that receive noise would be high and while it’s possible to hang an antenna up inside the room, getting it out on a balcony would work much better. The motel at Yalara (where the accomodation is near Uluru) had a decent but all metal balcony.

The first attempt had the wire antenna on the outside face of the balcony. Reception and transmission was not good. Our room was on the second floor and there was a small tree just across a path so a sugar packet was tied to the end of the wire for a bit of weight and I threw it out to the tree. This worked much better.

The end fed wire was cut randomly and is about 4m in length (very short for the 20m band). A small counter-poise of about 1.5m was just laid out on the floor. A QRP Z-match antenna tuner was used and a NanoVNA was used for initial tuning. The Z-match was able to provide a very good match, no external Unun was needed. No doubt there are losses but my signal was received around the world so they can't be too bad.

The Z-match has an SWR indicating LED (you tune for minimum brightness) but I also experimented with a simple RF current detector and found that brightness is maximum close to when the SWR is at a minimum.

There’s promise in this simple RF current detector and in an absolute miniature equipment setup I might opt for one of these combined with receive noise peaking to indicate antenna resonance.

Having said that, the NanoVNA is a remarkable piece of pocket sized test equipment, smaller than any antenna analyser and very capable.

Weak signal operation in a poor location begs for WSPR operation and the rig of choice for me is the QRP-Labs QDX which has many advantages including being pocket sized. I powered it from a block of 8 AA NiMH batteries which were able to run it from about 6pm until 3am local time with 10% transmission. 

WSJT-X was run on an M2 MacBook Air prevented from sleeping with the Caffeinated app. One of the benefits of using the QDX is that rather than mixing WSPR audio tones up to SSB audio, Hans cleverly measures the period of the audio cycle and directly sets the RF oscillator to the right frequency. This makes for a very pure transmitted signal and I’m convinced that WSPR transmitted by one of Hans’ recent transceivers is more easily decoded than the same power from a sideband transmitter.

One 2 minute transmission was reported by 41 stations which is pretty good going given my remote location and compromise antenna.

In this case my end fed wire antenna was black insulated hookup wire. It was not easy to spot from outside and I know that some stations use wire-wrap wire which is virtually invisible even close by.

If you ever get the chance to visit Uluru, go for it. It’s a remarkable feature of the landscape.

If you will be in a motel anywhere in the world consider digital QRP operation.

Tech news spot on ABC Nightlife

Billboards are said to be one kind of advertising that can't be blocked or skipped. That's all about to change with a revolution in outdoor advertising in Switzerland. 

Also, the devastating Windows CrowdStrike raised many questions, but it looks like Microsoft is working to make Windows more robust in the face of software bugs that could bring it down. 

Plus, flying cars were one of the features of the Jetsons cartoon vision of the future, and now it seems like regulators are preparing for this new world happening soon. Nightlife Tech Guru Peter Marks joined Philip Clark to discuss the latest news in technology. Listen here. 

Eyeglasses in Australia are hugely over priced

A recent podcast from Freakonomics titled Why do your Eyeglasses cost $1,000? explains the EssilorLuxottica monopoly we face here in Australia as well as the US.  Their markups are described by one analyst as "obscene". They mention Warby Parker as a possible monopoly breaker but sadly they don't seem to have come to Australia.

My prescription is relatively complex with astigmatism and I've paid $800 for progressive lenses and $300 for computer distance reading glasses.

Despite efforts by eye testers I've been able to get a copy of my prescription and recently ordered some new reading glasses from Zenottic in China for $55 (plus $10 shipping). They are perfect and the frames seem as good as any in the local shops.

I think it's a scandal that we pay 5 times the price, or more, to buy locally. It does take some care to get the prescription down correctly as well as inter-ocular distance but once I got it right I'm able to cheaply get additional pairs.

Note that EssilorLuxottica owns Sunglass Hut, OPSM, Oakley, Ray-Ban, LensCrafters and many more.

Tech news spot on ABC Radio Nightlife

This week on ABC Radio Nightlife, we talked about Samsung's product updates and how much they look like Apple products, a new way to migrate your photos from Google to Apple's cloud, future cars that won't let you speed, Android's coming desktop mode, some old technology (8 inch floppy disks) that are finally being retired and the US ban on Kaspersky Anti-Virus. Listen here. 

Alternative fan control for a Saxon wood heater

Our home came with a Saxon wood heater but the advertised automatic fan control circuit has never worked and I must get down on the floor to turn the fan on or off manually.

The heater works by heating a cement plate at the top of the firebox and a fan runs air over the top of it which warms the room. If the fan isn't on the heat goes up the flu. If the fan is on when the fire isn't going well it cools the firebox and may extinguish the fire. 

I enquired at the company about getting this fixed or getting a replacement board and they referred me to our local agent who basically said they knew nothing.

The circuit certainly looks quite simple although the markings on the IC have been cleaned off.

My solution was to purchase a temperature controller XH-W3001 that can be used either in heating mode or cooling mode. I've set it to come on when the sensor is over 30C indicating that the fire is hot inside.

The sensor range is only up to 120C so I've put the sensor at the back above the heater. The XH-W3001 was AU$5.98 which seems very reasonable. The mains wires are rather flimsy but should be OK for switching a fan.

The way it works is a little counter-intuitive. It has a "heating mode" and a "cooling mode". I'm using it in cooling mode where the output comes on when the temperature exceeds the left hand value and goes off when the temperature drops below the right hand value.

I've set left to 34C and right to 30C. The sensor is at the back just poked in to the top cavity. It seems to be working well and the cat is very impressed.

Broadband RF generator (AKA eBike charger)

My new eBike came with a charger. Even though it's about 10m away from my ham shack the radiated noise level is impressive. 

Here's the "transmitter":

Here's the inside view:

Even with external clip-on ferrites on the mains and output cable there is little difference. How can it be legal to sell noise makers like this? Are all the certifications fake or just incredibly poor standards?

As Ralph, VK3ZZC, suggested I have added 0.1uF silver mica capacitors across the large electrolytic smoothing capacitors on the output and this has made a noticable improvement on the radio.

Talked tech on ABC Radio Nightlife

I joined Philip Clark on ABC Radio's Nightlife program to talk about technology news including new legislation to combat faked sender IDs on scam text messages, YouTube live stream hacks to promote crypto scams and a look at the new ARM based Microsoft Surface laptops that are challenging Apple.

Audio here.

In the story I talked about trying out the new Microsoft Surface laptop powered by ARM. It's a nice looking and feeling laptop, quite similar to the M2 MacBook Air which I imagine it is competing with. Fit and finish is excellent. More ports than Apple and slightly better value in terms of price per GB of storage and RAM.

There's a new Microsoft only key on the right hand side for summoning Copilot AI features.

I pushed the key and not a lot seemed to happen but I guess, like Apple these new features are being rolled out over time.