Wednesday, January 30, 2019

RTL-SDR for spectrum analysis

Since getting back in to RTL-SDR for my recent foray into decoding DMR, I found that these are a very useful (and low cost) bit of gear.

At the last ham radio meeting at Dural, I bought a Shure radio microphone and when I got home I wanted to find out what frequency it was on. Cranking the knob on a receiver was taking forever so I decided to look into scanning broadly with RTL-SDR.

There is a bundled tool called rtl_power which seems perfect for this but it creates a CSV file that's a bit annoying to look at or graph. Now I've stumbled upon RTLSDR-scanner.

RTLSDR-scanner is a python module which you run from the command line. You give it a low and high frequency and it quickly scans and displays a nice graph which can also be exported and looks like this:

(Click images to enlarge by the way). RTL-SDRs don't have much dynamic range so I don't really think this would be good for real spectrum analysis tasks, like finding spurious emissions from transmitters, but for finding the output of a mystery radio mic (622MHz by the way) it was perfect.


There is some great software around for driving RTL-SDR and other SDRs. One that looks terrific is Spektrum but I can't get it working on my Ubuntu or Windows machines here.

Mac Malware - do not update flash

Two good friends have recently had their Apple macOS machines infected with annoying malware and I'm pretty sure the vector was downloading and installing (with authentication) fake updates to Adobe Flash.

I saw this amazing display recently, all on one page.

Use of Flash is almost zero these days and if you really need it I suggest running the Chrome browser which has it built-in.

If you think you have malware on your computer, I can recommend ClamAV which is open source and free. Friend Gerald said that ClamAV didn't find everything though "So it looks like ComboCleaner finds threats that ClamAV does not. Although CC won't delete them, but uses the fear to promote subscription."

He's technical so once he had a name of something found by ComboCleaner he used find / -name XXX to find the path to each suspect file and then deleted them manually.

Having said all that, I don't run a virus checker on my Macs and haven't had trouble, but that's partly because I'm very skeptical of things I install from the internet.

Sunday, January 27, 2019

ARNSW Home Brew Group - DMR here too

Today we had a meeting of the home brew group out at ARNSW in Dural. The first surprise (to me) was the wonderful new tower that has been erected on the site. I'm told that the antenna for the UHF DMR repeater will be right up the top when it's ready.

The other surprise was a large number of valve radios have appeared in the sale items. Apparently this is just the tip of the iceberg and a large collection has become available. I wondered if this was from Jack in near by Castlecrag but apparently that's not the case. I guess the generation who have collected these lovely old mantle receivers has had a touch of KonMarie and aren't seeing enough joy to hang on to them.

Peter, VK2EMU, is building a valve power amplifier and along the way he's taken a diversion and built a beautiful valve tester in a wooden box. The front panel is marked with, I assume, a soldering iron. There's a little door at the back where you pull out the anode lead and inside there is storage for other valve sockets.

A clever part of the design, which I believe is from Drew Diamond, is that the anode is at zero volts and the cathode -600V or so. This means that you don't get killed if you touch the top of the valve.

Peter's diversion reminds me of Donald Knuth's diversion into typesetting while writing the art of computer software. The valve PA is coming along though.

Speaking of valves, here's just some of the valve radios on sale, typically for about $20 each.

Finally we came to the main presentation by Paul VK2GX with an introduction to the DMR radio system. A terrific talk.

When Paul finished I demonstrated decoding DMR off air using an RTL-SDR and the DSD+ software which I wrote about here recently.

Keen to learn more about this I've gone ahead and ordered a TYT MD-380 Transceiver for AU$127 and will report back when it arrives in a few weeks. The low price of DMR gear I think may spell the death of alternative commercial digital radio standards like D-STAR.

Saturday, January 26, 2019

Listening to DMR without a DMR radio

It's not too hard to listen in to DMR digital radio traffic with just a low cost RTL-SDR dongle and some software.

I can pick up the Sydney repeater on 439.5MHz pretty well, even with a non-resonant antenna. There's a good list of frequencies in Australia on VK DMR Info site.

(Click to enlarge the screen shot).

Here, on Windows 10, I'm using SDRSharp piping audio over to DSD+. I followed the instructions found via the RTL-SDR page but in summary, you need VB-Cable to route audio out of SDRSharp over to the DSD+ program.

Demodulation is set to NFM but the bandwidth is wound out to 12kHz. I turned squelch off and also turning off "Filer Audio" made it work much better. Adjusting the audio output level in SDRSharp is also important for good decode.

Here's how it sounds:

At the home brew group meeting on Sunday I understand there's a talk on DMR so I'll be interested to learn more.

Wednesday, January 16, 2019

Nice WSPR Watch review from a fine blog

My thanks to Bas over at the excellent PE4BAS ham radio weblog for his kind review of the recent updates to WSPR watch.

He seems surprised that there are free apps in the iOS app store but the reason, in this case, is that I wrote the app for my own use as I find the site isn't really mobile friendly and I like being able to quickly do a search to see how my station is performing.

Bas missed my favourite of the new features which is multi band handling with colour coding. It all looks very pretty.

If you use WSPR watch and haven't already, please leave a review as it helps other people find the app and also makes me feel happy. I'm also open to suggestions for new features but no guarantees on when I'll get to them.

There are a number of sites that scrape and add value in different ways: is a great service although it is sometimes very slow or even unresponsive. I'm sure all of us who scrape data from there wish there was an API we could use.


Spurred on by this attention, there have been some updates to WSPR Watch. You can now search the spots for a given callsign (or part) and the traces on the map fade over time.

Sunday, January 06, 2019

Vanlife van interiors - we can learn from the experts - Gypsies

While re-modelling the interior of my tiny camper van I've become fascinated by the interior designs people come up with for these compact living spaces. Recently I struck gold by searching for "Gypsy caravan interior" images.

While clearly designed for cold climate, it's fascinating to look through these.

Check out Low-Tech Magazine

I've just stumbled across a real gem called Low-Tech Magazine. It's a rich collection of stories that provide evidence, if we need it, that sometimes the old ways of doing things are superior to our modern, high technology and high energy use, ways.

They talk about how we used to keep warm at home with a combination of warm clothes and radiant heat - rather than heating the air of the whole house and how ceiling fans are a much better idea than central air-conditioning.

There are interesting pieces about energy storage options including compressed air, as shown above, and insightful comments about how the internet has got faster but web sites have gotten slower.

There's even a solar powered version of the site, which may not be online if the sun isn't shining.

Tuesday, January 01, 2019

Days like this makes me appreciate our solar panels

It's pretty hot here this week. Today it's 32C outside, but inside it's a very pleasant 24C. The wonderful thing is that the house is cooled totally with power from the panels on the roof.

The system generates up to 3.3kW and as the panels are on the north west face of the roof (as you can see the hot water panels are on the north face) we get peak power in the afternoon - which works well on days like this.

I calculate that the system will pay for itself in electricity savings and rebates in about eight years but on days like today we normally wouldn't run the air conditioner except that it's free.

Our quarterly power bill is about $240 and I'm told by the state government's plan comparison site that we can save $100 off that by switching plans - I'm a little sceptical but we'll see.

We did look at adding a battery but at the moment the numbers don't make sense given the lifespan.