Tuesday, March 31, 2020

Class E PA for WSPR with home brew variometer in the antenna coupler

Ross, VK1UN and EX0AA, is a frequent traveller and likes to get on air with WSPR under challenging conditions including using stealthy end fed antennas deployed from a window from hotels or flats. Currently he’s transmitting in Bishkek, Kyrgyzstan and getting amazing results even on 160m or lower.

His current configuration is interesting in several ways, he uses an Ultimate3 Beacon from QRP-Labs to drive a very efficient home brew class E PA that is coupled to an end fed wire antenna via a coupler with a home brew variometer.

The Class E PA is designed for 12V and 10.09W which, with an IRF530, gives a MOSFET R of exactly 4 Ohms and the PI output network of exactly 4 Ohms input and output as well. 

Why not 50 Ohms?

These PAs are designed for a single series C from PI out and shunt L (variometer) to match to a long wire. Also, he has a decent 4 Ohm load that can be used to test stage one of these PA's operation at 4 Ohms. The main strategy with these PAs is that, if the antenna changes such that the input |Z| is different, he can change the series C and L on variometer very easily.


L4 is the variometer and the secret to easily tuning different end fed antennas. When Ross had a good match direct from the PA via a series L (FET match) and then series LC match to the wire with a lumped inductor, a change the the wire's |Z| required a lot of work calculating and re-winding a new toroid. A variometer is a low cost and easily adjustable alternative to a roller inductor and can be home built.


The other advantage is, that in a 4 Ohm PI out can use 50V SMD caps without exceeding ratings and can get all values unlike those available as 500V caps.

Ross has built versions for several bands but most recently a 160m version which puts out 3W at 5.75V with good results and has a near perfect D-S waveform and good looking spectrum.


DC power input is very modest and efficiency is about 95%.


Here's the PA.


Ross is well received on WSPR from his remote location. Here's the display in the new WSPR Watch for macOS.


Thanks to Ross for sharing this project with us.

Saturday, March 28, 2020

ARNSW Home Brew Group meeting via video conference

With our normal Dural meeting off this month due to the COVID-19 pandemic, we moved online and had a group meeting using Skype. It went pretty well.


Thanks to everyone who participated and we'd love to do this again in the future.


Perhaps, as we meet physically every two months, we could alternate with an online meeting?


Next Skype meeting is planned for noon on Sunday 26th of April 2020.

Tuesday, March 17, 2020

ARNSW Home Brew group & Trash and Treasure meetings suspended due to COVID-19

Today I heard from Mark Blackmore and Peter O'Connell that physical meetings at Dural NSW of the Amateur Radio NSW Home Brew Group and the Trash and Treasure events are to be suspended. Mark suspects that this may be right up until September, but it depends on how things pan out.

This is very wise as the age profile of the attendees includes some people of an age that getting the novel coronavirus could be devastating.

I am recovering from a quite unpleasant bout of flu. As I wasn't eligible for a test I have no idea if it is the flu. The symptoms all line up - headache, sore throat, temperature, dry cough. For me, it wasn't serious enough to warrant a doctor and symptomatic medication was enough, although it was rough particularly at night. It's taken about ten days so far and I'm feeling better each day.

Social contact via Ham Radio seems like an excellent option at times like this. As Bill, N2CQR, points out in the latest edition of the Soldersmoke podcast there is no evidence, at this stage, that the virus can be transmitted via amateur radio, although there is some concern about 80m.

Saturday, March 14, 2020

Radio Australia Shortwave broadcast antennas in use again!

This weekend there is a special event under the callsign VI3RA where amateurs are able to use the amazing antenna array that used to be used for Radio Australia at Shepparton.

I listened in on 40m using the VK2OB KiwiSDR at the CSIRO Australia Telescope Compact Array at Narrabri NSW. As expected, the signal was excellent.

Of course I really wish we were still broadcasting on shortwave to Australia, the Pacific and Asia from this or another facility but sadly that is not the case.

Here's a short recording.


These Web SDRs really are a fantastic development.

Thursday, March 12, 2020

Ham Radio on a Chromebook?

Chromebooks are generally low cost, low spec laptops that run a simpler operating system than Windows, Macs or Linux machines. As there’s less going on, the battery life can be excellent, sometimes ten hours or more. The Chrome browser runs really well and if you live in the cloud, and do everything through a web browser, a Chromebook is a great choice.

Chrome OS is very secure and updates itself regularly. The Google suite, which includes all of the office apps you might want, can be set to cache a copy of docs locally so you can work on them offline.

Under the hood, Chrome OS is a locked down version of Linux. There have been ways in the past to turn off this security so that other Linux apps could be installed but that was risky. In 2019, Google announced proper Linux support for Chrome OS.

To maintain the secure environment, the official Linux environment runs in a virtual machine. There’s a handy way to copy files over to your Linux home directory right in the Files app but the Linux environment can’t access the Chrome OS files unless you explicitly choose “share with Linux” in the Files app.

What you get is a terminal and a pretty standard Debian 9 world with a few things installed such as git, vim and ssh. Using apt you can install many popular ham radio packages such as fldigi and wsjt-x. Here is fldigi running next to an Android app on Chrome OS:


The virtual Linux environment has access to networking, USB ports and the ability to draw windows on screen and it seems to run quite well. The bad news, at the time of writing, is that sound doesn’t seem to work. I can see likely looking sound devices listed in the PortAudio device popups but no sound seems to come in or get out.

There’s a ticket open about audio capture, it appears to be an issue that the Linux VM needs a way to be given permission to access audio devices on Chrome OS. Work needs to be done both by Google on Chrome OS and by the Linux kernel maintainers on Linux.

Note that running the Linux virtual machine is said to cut battery life by about two hours.

Modern Chromebooks can also install and run many Android apps by simply using the Google Play store. Android apps seem to run in a phone sized window and work pretty well. The first ham radio app I went looking for was SDR Touch but unfortunately it’s not listed. My guess is that the special access it needs to talk to an RTL-SDR is not possible on the Chrome OS platform.

Chrome OS Observations


The micro SD card seems like a good way to expand the small built-in storage (64GB in my case). I inserted a card with music on it but when the Chromebook wakes from sleep it complained that I hadn’t unmounted the card before ejecting it. Battery power had drained much more than usual during this sleep as well, perhaps it was waking to check the card or something?

I find the icon for settings, a cog, is visually similar to the icon for screen brightness, a sun circle. Several times I’ve clicked the brightness hoping to get to settings.

The “shelf”, which is like the dock on macOS, can be used to launch applications including those in the Google suite. It took me a while to figure out how to put website launch buttons there. The trick is to go to the site, click the three vertical dot menu top right, open “more tools…”, choose “create shortcut…” and then make a shortcut to the site. These shortcuts appear on the “desktop” which can be accessed from the search key. Show the desktop and drag the icon to the shelf. This should be easier.

Lenovo Chromebook S340-14


I purchased this 14 inch Chromebook for $397. The main reason, apart from learning about Chrome OS, is to use it for reading mail and news in the morning while having breakfast. The morning routine is exclusively looking at web sites in a web browser so a web only machine is a perfect choice.

This Chromebook has a high resolution screen for the money. 1920x1080 with a matt surface. It’s said to be 220 nits in brightness but I find the contrast quite low. Many Chromebooks, and in fact surprisingly many low cost Windows laptops have screens that are just 768 lines high and this is not enough for viewing web sites that increasingly overlay the page with annoying requests to agree to cookies, sign up for newsletters, or have you watch floating videos.

The chiclet keyboard is good and the trackpad works very well - not to Apple standard - but responsive.

This laptop has USB-C ports on both sides, something I wish Apple would do on all laptops, so you can charge from either side with minimum cord crossing. It comes with a 45W USB-C charger but charges just fine from various USB-C chargers I have around the house. Other ports are two USB-A ports, headset, microSD slot.

CPU is Intel Celeron N4000 (2C / 2T, 1.1 / 2.6GHz, 4MB). 4GB RAM and 64GB eMMC storage. If you use Google’s cloud storage, this is perfectly fine. The camera is pretty bad. Sound from the speaker is tinny.

Running Chrome OS means that the laptop boots quickly, wakes instantly, and runs the Chrome browser better, I think, than any other platform.

Battery life is good. In my use as a breakfast news consumer, I charge it every few days (perhaps 4) and don’t feel panic as the battery level drops. It does seem to run down rapidly towards the end though.

I'm a big fan of USB-C, I know it's not cool to say so. Plugging a 4k monitor in via a USB-C cable worked perfectly and a second desktop appeared with plenty of space. It defaulted to tiny text but that's easily changed in device settings.


As expected, this single cable not only passes video and audio but also charges the laptop.

Conclusions


If you’re looking for a low cost laptop for browsing the web, particularly if you use Google’s mail and other cloud tools, a Chromebook is a great choice. I would recommend one to a non tech savvy user just as I would suggest an iPad.

The recent feature of being able to run Linux apps is interesting and means that as a unix user I can install power tools like Visual Studio Code, python, even graphical Linux apps.

Ham Radio on a Chromebook?


At the time of writing, the main missing piece for Ham Radio applications is access to sound. Devices are listed and I’m sure one day soon this will be solved. So, ham radio on a Chromebook? No. Not quite yet.

This conclusion is in line with Betteridge's Law.

Monday, March 09, 2020

Enjoyed the 48th Model Railway Exhibition at Forestville

One thing I'll definitely miss as we move away from this area is the annual model rail exhibition that is just up the road. Here's a few impressions:






WifiTrax is a good idea but it didn't work very well in a busy environment with lots of hot spots.



Hearty congratulations to the North Shore Radio Modellers Association Inc. who run this fantastic event.

Tiny toaster ovens are the best ovens

As part of the downsizing project here we threw out or sold a lot of things. Our old toaster oven had been damaged by me cleaning it with oven cleaner. Big mistake on aluminium walls!

I really missed the toaster oven. The small internal volume means that it gets up to temperature in seconds and the heat is very even.

After struggling with the big oven in the kitchen for a few months I decided to lash out and purchase a replacement. The Sunbeam 9 litre shown here at Myer was available at The Good Guys for $59 so that's where I purchased it.

The signature dish in one of these is a ham, cheese and tomato toastie, but tonight we had little quiches. Very nice.


Wednesday, March 04, 2020

How to see LoRa on an RTL-SDR waterfall

I've tried to see the LoRa chirps in the past but they were always too quick. John, VK2ASU, has figured out how to slow down the chirps and spread the spectrum enough to see this:


Here's the settings used:

LoRa.setSpreadingFactor(20);
LoRa.setSignalBandwidth(62.5E3);

Thanks John!

Decoding a Digitech Wireless LCD Thermometer

Just picked up a AU$20 indoor/outdoor wireless thermometer from Jaycar. It mentions on the back that it uses 433.9MHz so I connected an RTL-SDR and ran the omni decoding rtl_433 command line tool. Simply installed using apt on Ubuntu.


The remote FT-004-b temperature sensor sends a reading once every 60 seconds. There's a little LED that blinks just before it sends. Here's the setup.



rtl_433 can output decoded data in a variety of formats: kv|json|csv|mqtt|influx|syslog,  so this could be handy for logging temperatures. rtl_433 can decode about 150 different devices and there is documentation on how to add more.

It supports the following modulation types:

OOK_MC_ZEROBIT :  Manchester Code with fixed leading zero bit
OOK_PCM :         Pulse Code Modulation (RZ or NRZ)
OOK_PPM :         Pulse Position Modulation
OOK_PWM :         Pulse Width Modulation
OOK_DMC :         Differential Manchester Code
OOK_PIWM_RAW :    Raw Pulse Interval and Width Modulation
OOK_PIWM_DC :     Differential Pulse Interval and Width Modulation
OOK_MC_OSV1 :     Manchester Code for OSv1 devices
FSK_PCM :         FSK Pulse Code Modulation
FSK_PWM :         FSK Pulse Width Modulation
FSK_MC_ZEROBIT :  Manchester Code with fixed leading zero bit



Thanks to John, VK2ASU, for the nifty 433MHz SMA antenna.