One of the members at the radio club Merlin suggested trying out this sensor decoding program for the RTL SDR receiver. You can view and order one online for just a few pounds.
The software RTL 433 is a generic sensor decoder, and it will decode and display a variety of environmental data. Despite its name the frequency can be defined in the setup, and sensors can be found on 315, 433, 868 and 915 MHz depending on your location.
In the UK 433.92 is the most popular, and so this is a good place to start. Firstly you will need to install and have run the RTL SDR, you can do this by plugging it into the USB port on your computer and waiting. Windows will helpfully install the incorrect drivers, and this can be resolved by running Zadig. Follow the instructions here. The Quickstart guide is also online.
If your running Pi, Linux or Mac then you will need to look up the instructions on the link given for installation instructions.
Once the RTL dongle is installed, then the addition of a good 433 MHz antenna will allow the reception of some interesting signals, even if you just have the default magnetic antenna the chances are you will pick up some local traffic.
The RTL has lots of diverse supported software, you can find a list available at RTL-SDR.com
Merlin also pointed out that while the program will run from the windows explorer it is best to create a .bat file in notepad.
If you haven’t already seen this started with Part 1 and Part 2
This evening I tested 2 common micromagnetic aerials often used as quick fixes for using the handy in the car. The last antenna is a stubby found on the Motorola MT200 series handhelds, often used by amateurs for 433 MHz.
Our first micromagnetic antenna is around 300mm (12 inches) long and has the very lossy thin coax.The antenna surprising has a match point on both 145 and 433 MHz
You can see from the VNA plot it makes a good effort on both frequencies.
Our second micromagnetic antenna doesn’t fair as well, providing a poor match on 145 MHz, and a poor match on 433. It’s slightly shorter than the first version around 25cm (10 inches)
The VNA plot shows the match at both 145 and 433 MHz
Our last candidate is the stubby found on Motorola MT2000 handsets, these are often used on the 433 MHz amateur bands. The handheld and antenna look like this.
The antenna doesn’t do too bad on 433 MHz but it’s clearly been optimised for further up the PMR band.
It’s worth noting on 433 MHz using the very thin RG174 coax you should expect to lose 50% or more of you power before it even reaches the aerial. Yes, they will often work better than the stubby in the car, and they may very well do exactly what you want for local repeater access but it’s worth knowing the limitations.