Wednesday, March 29, 2017

Decoding pagers with rtl-sdr

This works.

$ rtl_fm -o 4 -A lut -s 22050 -f 148.137M - | multimon-ng -t raw -a POCSAG512 -a POCSAG1200 -a POCSAG2400 -f alpha /dev/stdin
Warning: -o is very buggy
multimon-ng  (C) 1996/1997 by Tom Sailer HB9JNX/AE4WA
             (C) 2012-2014 by Elias Oenal
Enabled demodulators: POCSAG512 POCSAG1200 POCSAG2400
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Tuner gain set to automatic.
Tuned to 148401600 Hz.
Oversampling input by: 12x.
Oversampling output by: 4x.
Buffer size: 7.74ms
Exact sample rate is: 1058400.010094 Hz
Sampling at 1058400 S/s.
Output at 22050 Hz.
POCSAG512: Address:  158460  Function: 0  Alpha:   57973-1 
POCSAG512: Address: 2007607  Function: 1 
POCSAG512: Address: 1741522  Function: 0 
POCSAG512: Address: 1705329  Function: 0  Alpha:   69u'2-88

multimon-ng comes from here. I found the frequency by running CubicSDR.

This post is a note to future me.

Wednesday, March 22, 2017

Logitech Brio 4K Pro Webcam review

USB-C is clearly the future of desktop peripheral connection and it's great to see products appearing that leverage this new plug.

I plugged the new Logitech Brio 4K Pro Webcam into a 12" Macbook via the USB-C cable that came with the laptop for charging, it's the first time I've used it for anything more interesting. Here's how it looks (I hadn't removed the protective plastic at this point).

The camera itself is 27mm high and 102mm wide. There's an "on" light, the lens, a microphone and presumably a flash along the middle. Below are left and right microphones.

Note that I did not go and download any extra software before plugging it in so that I could see how the device works "out of the box" on macOS. All good! The camera simply appears as an extra device in standard video apps including FaceTime and Photo Booth.

Here's a comparison with the built-in FaceTime camera in the MacBook. On the left is the Apple built-in camera, on the right is the Logitech Brio.

The Logitech camera is more wide-angle which would be better for capturing a meeting room or small group for a video call. I have to say that the Apple camera is pretty good and if you just want to have video calls from an Apple laptop then you probably would just use the built-in camera.

Image quality seems a little soft, I'm not sure that the auto-focus works as I'd expect.

Physically the camera's stand is very clever and the rubber coated clamp mechanism allows the camera to be mounted on a laptop screen or to stand on a desk with ease.

You can squeeze the clamp and it stays put either gripping a screen of various widths or just standing on a surface. The little stand disconnects to reveal a standard 1/4" tripod socket which is very convenient.


Additional "settings" software is available for download. It takes almost 70Mb of space once installed which is a little more than I'd expect.

Image quality viewed through the settings software is much better which suggests that video conferencing apps are not making use of the 4k resolution. Also there is the option of a 90 degree wide angle mode - so the default is zoomed. (Click the image below to zoom in).

The first panel lets you zoom the camera in and digitally pan left, right, up or down.

There are also additional controls for the image.

Surprisingly (to me) you can run the camera control app along side another app using the camera and make adjustments, here it is zooming in while using FaceTime. (I'm available for a Terminator re-boot by the way... oh).


The Logitech Brio 4K Pro webcam retails for AU$379.95. On a Mac it worked "out of the box" with existing apps including FaceTime and Skype. It did not work with iMovie X for some reason.

If you have a computer with USB-C then it's fantastic to have a peripheral that can plug right in. Logitech includes a USB-C to USB-A cable in the box so no problem if you haven't moved yet.

The image quality is good but looked a little soft, this might be that what I'm comparing to has done extra sharpening. Detail in shadows is better than the build-in camera on an Apple Macbook but might be much better than some other laptops.

As a camera for videoconferencing the 4K resolution is really a waste but the ability to zoom in on part of the frame makes the extra pixels useful.

My thanks to Logitech Australia for the loan of a review unit.

Monday, March 13, 2017

Simple ground stake for supporting squid pole

I was very impressed by Peter, VK2AQJ's method for standing up a squid pole for supporting his portable antenna and decided to reproduce it. Some 20mm angle aluminium and angle brackets was purchased at the local hardware. The aluminium I got was 1.5mm thick and 1m long.

Hack-sawed a point to make it easier to push into the dirt.

The right angle bracket is bolted on and can be used to push the stake in with your foot.

Peter had also added a screw terminal so it can be used as a ground connection but as I'm using a dipole decided to skip this.

In use I feel that 1.5mm aluminium and the angle bracket are a bit low in strength but probably OK as this is QRP we're doing here.

Sunday, March 12, 2017

QRP by the harbour report

Inspired by Peter, VK3YE's famous "QRP by the bay" events, we decided to try a Sydney equivalent titled "QRP by the harbour".

About a dozen enthusiasts turned up at McIlwaine Park at Rhodes on a beautiful Sunday afternoon.

We put up an inverted V antenna for 40m suspended from a 6m squid pole lashed to a park bench - the ends of the dipole were tied to branches of nearby trees. There was also a short vertical for 80m and an end fed for 80m but in the end I think the 40m dipole worked the best.

Being a contest weekend there was no problem getting contacts but for me the highlight was a contact with Peter VK3YE who was pedestrian mobile in Melbourne, both ends QRP. Here's the antenna:

Here's a close up of the light weight balun and how the antenna wire is carried on a $3 mains extension cord winder from a hardware store.

Some experienced field operators, such as Peter Jensen, VK2AQJ, brought impressive portable gear:

Lessons learned

To publicise the event, I copied Peter VK3YE and created a Facebook page, but I also created a Facebook event for this year's event.

The page will serve as a promotion for future events and the event was useful for people to confirm that they were going to attend and also share the event. To promote the event I decided to spend up to $30 on Facebook, in the end it only used up $16 of the budget but I think it was worth while as the event was shown in local Facebook users news feeds who have shown an interest in ham radio. You get these nifty reports too:

Peter, VK2EMU promoted the event on the ARNSW Sunday broadcasts for the weeks leading up to it and also on VKHAM. I had a note in Low Key but I fear it was too late.

The only downside of the location was that while we had chosen it because of the proximity of both rail and bus stops, there was rail work going on so no trains were running and because of this buses were irregular. Being a lovely day, the car park was full and it was hard to find a good spot to set up.

ABC RN Tech - CIA hacking revelations

My spot on ABC Radio National about the WikiLeaks CIA hacking revelations.

Saturday, February 25, 2017

Wyong field day 2017

The predicted rain held off this year and it was great conditions for the annual Wyong Amateur Radio field day.

As always the ARNSW Home Brew group had an excellent display of home built gear.

I cheated and showed how well I had installed a Bitx40 module in a plastic box. The best bit of my construction was the gutter guard speaker grill. Peter VK2EMU, John VK2ASU, Kevin VK2KB and others were often mobbed with enthusiastic crowds.

There was retro gear (if you don't count the 3D printed coil form):

A fascinating demo of the pulse width control of a servo motor as using in radio control planes.

Again this year I had the pleasure of assisting David Rowe on the FreeDV / codec2 exhibit.

We were kept busy with many enquiries and also people purchasing SM1000 units.

A real standout for me was the presentation by the Bureau of Meteorology's Space Weather Services. They have some excellent tools for ionospheric prediction and even a downloadable application for Microsoft Windows.

Congratulations to all involved in the field day this year, it was very smooth and seemed like a terrific turnout given the threatening weather. I can't wait until next year.

Sunday, February 19, 2017

Low cost laptop for Ham Radio applications - HP Stream 11 review

A friend I visited recently was having trouble with his computer which turned out to be an old tower machine running Windows XP connected to a CRT monitor. While he could do what he wanted to it was terribly slow and even powered itself off mysteriously at one point.

While the netbook era appears to have passed, I wondered if there was a modern alternative that would do the job without breaking the bank?

The cheapest modern laptop with Windows 10 was an HP Stream 11 R007 available at Harvey Norman for AU$238, showing as in stock. There was one on display in the store but I was told there were none actually for sale, would I consider something better?

Bait and switch perhaps? I resisted all the arguments from the sales person who was essentially suggesting spending at least hundreds of dollars more, and selected an HP Stream 11 Y009 they had for AU$248. On paper the specs seemed the same.

The sales person warned me that this was not a fast machine. I asked if it was "fit for purpose" and he said yes but he would make a note on the invoice that I had been warned.


HP Stream 11-Y009TU
* 32GB Flash storage
* 1366x768 display
* 1x USB2 port
* 1x USB3 port
* HDMI port
* Micro SD card slot
* Dual band Wifi
* Bluetooth
* Combined audio in/out jack
* Video camera & microphone
* Intel Celeron N3060 dual core 1.6GHz CPU
* Windows 10 Home


Nice looking, solid construction, bright blue (there are other colours).

The keyboard is good and the display is fine for the price. The battery is built-in which I'm used to from Apple gear and I think this helps make the device seem more solid. The track pad seems very good and support two finger scrolling, tap to click and three finger gestures - unheard of a few years ago.

Initial setup

After power up and Wifi connect it was time to kick off the initial setup and Windows updates. This took a long time, it took about three hours until all was done and it's not due to a slow internet connection.

Along the way was an attempt to get me to register for McAfee anti-virus which I declined.

Cleaning up the "bloatware"

The 32GB flash disk is mostly filled with Windows and bundled software. I uninstalled: McAfee LiveSafe, Microsoft OneDrive, Dropbox, Skype Preview, WildTangent Games, Office 365, Get Office, HP ePrint, HP Support Assistant, HP Support Solutions Framework, Microsoft Solitare Collection, Microsoft Weather, HP Jumpstart (187MB), HP Jumpstart launch, HP Registration service, HP System Event utility, Mail, Calendar.

I installed: Google Chrome browser, Fldigi, WSJT-X.

The start menu had dozens of annoying things in it which I unpinned.

At this point there was 5.9GB free of 27.8GB storage. This seems small by modern standards but is actually a lot compared to my friend's XP computer.

I created a USB Recovery drive using a 32GB USB key, this took maybe an hour.

Even though McAfee was installed it turned out that Microsoft's Windows Defender was already installed so I let that scan the disk so it would stop complaining.

Chrome was set as the default browser - it's funny how Microsoft tries to talk you out of not using their Edge browser at that point and even later when you launch Chrome. This seems anti-competitive.

There was another Windows update and I got a warning that disk space was short. The Disk Cleanup utility was run and I clicked "Cleanup system files". This deleted 13.3GB of "previous Windows installations".

Is 32GB disk enough?

It was astonishing to get a low disk space warning after simply updating and removing lots of bundled software. 32GB should be enough and I've run Linux on 3GB disks in the past. Both Microsoft and HP are to blame for the bloatware that comes on these machines. At least there was only one third party anti-virus package, sometimes there are several, which slows down the machine as well as taking space.

Is 2GB RAM enough?

Machines in this class are like Chromebooks in that they are not suited to running multiple large programs together. You wouldn't run Photoshop and Office side by side. Now that the initial updates and indexing has finished I'm smoothly running Chrome, Explorer and the Atom text editor together and all is well.

The bad

Bundled bloatware needs to stop if Microsoft is to avoid losing out to Chromebooks or iOS.  Initial update and messing around took a long time, don't expect to get started with real use on the same evening.

The processor is a bit slow sometimes and even Google Docs in Chrome was a bit sluggish initially.

Another USB port or two would be nice and I'm not sure about the combined headphone and mic socket - normal headphones work just fine though.

Some people might see the non-replaceable battery as a problem but I've rarely replaced a battery in a laptop - generally by the time the battery degrades it's no longer the main computer and relegated to some permanent task such as doing WSPR where it's plugged in all the time.

The good

Battery life seems excellent. After an hour's web browsing and text editing it's estimating 9 hours 38 minutes but I think 7 is closer to the truth with normal active use. Here's another probably inaccurate estimate:

The lower power processor helps battery life and I like the fact that there is no fan, which takes power and can be unreliable down the track.

Wifi seems excellent and I'm using my 5GHz network without any issues.

I really like the look of this laptop and the keyboard and trackpad are better than expected.

Ham radio applications

Fldigi, WSJT-X and SDR# all work well. SDR software typically taxes old CPUs and I wouldn't try running multiple programs while decoding SDR, but in normal use it seemed to keep up with the load.

The low res screen, just 768 lines, seems incredible to a macOS user but is typical in Windows land. It's annoying how shops don't tend to clearly display the screen resolution and you must dig into advanced display settings to find it. Some ham radio software, like the SDRuno for the SDRPlay would be difficult to run on this display but an external monitor would work well.

SDRUno works remarkably well under most circumstances, here's a video:

Provided that no other software is running, such as a web browser, and you don't zoom the spectrum in too far (no idea why that's a problem), it receives quite well and the user interface fits the screen.

I notice that WebSDR doesn't work very well, presumably not enough CPU to run the Javascript in real time, there's often repeating audio coming through.


A sub $250 laptop with long battery life and enough performance would be perfect for field use. I'm thinking of taking it out for QRP PSK operation and at this price it's not the end of the world if it gets a few bumps. Because of the solid state disk and fanless design it's probably pretty robust.

Screen brightness might be an issue in the field.

Prices do vary and I've seen these advertised at $299 or more. The box price at Harvey Norman is $328 so do shop around and get them to price match $248.

Update - runs better with Linux

Windows 2000 started to annoy me. It definitely got slower after a week and it kept trying to either sell me things or pop over the Chrome browser to tell me that their Edge browser was safer and faster than Chrome. 

I find it hard to believe that the operating system is a sales platform, it should be a "platform" for running software.

A recovery USB key was created, so that I could go back to Windows later if I wish and Ubuntu 16.04 LTS installed easily. (To get to the boot options on the HP Stream: power off, then power on and immediately start tapping the ESC key). Installing from a USB3 key using the left hand USB3 port was really fast and soon I was up and running with 30GB free instead of 3GB.

Sound, Wifi, and the function keys for volume and brightness all worked without any tweaking. Bluetooth sort of works but not with my mouse for some reason. To get it to sleep when the lid is closed I had to uncomment a line in /etc/systemd/logind.conf 


Battery life is still excellent.

The trackpad is rather sensitive and I had to disable tap to click. Sometimes clicking with the trackpad button moves the pointer and on Ubuntu I end up opening the trash instead of clicking where I wanted. Two finger scrolling works nicely.

Here's CubicSDR receiving an FM broadcast transmission.

I recommend this low cost laptop and if you can get by without Windows then Ubuntu is a good option.