The link between The Exorcist, Amateur Radio and Alan Turing.
A quick look at how the movie The Exorcist from 1973 has links to the late great Alan Turing via Mike Oldfield’s album Tubular Bells, Scotland and Amateur Radio. It’s Halloween so figured why not throw some horror in the mix.
When Mike Oldfield recorded Tubular Bells in 1973 he had no idea his first album on Virgin Records would be chosen as the soundtrack to The Exorcist later that year. Neither did he know that recording with Virgin Records would have an unintended consequence of hiding a secret message which dates back to 1926, shortly after World War One.
The Slow Scan TV images below will update every 30 seconds if I’m running the reciever for them. You never know what you might see so is kinda cool to see them appear in real time. I’m showing the last 20 images which have been decoded, usually from either 20m or 40m bands.
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
A literal term for SSTV is narrowband television. Analog broadcast television requires at least 6 MHz wide channels, because it transmits 25 or 30 picture frames per second (in the NTSC, PAL or SECAM color systems), but SSTV usually only takes up to a maximum of 3 kHz of bandwidth. It is a much slower method of still picture transmission, usually taking from about eight seconds to a couple of minutes, depending on the mode used, to transmit one image frame.
Since SSTV systems operate on voice frequencies, amateurs use it on shortwave (also known as HF by amateur radio operators), VHF and UHF radio.
A simple and quick project for detecting when a Yaesu transciever is transmitting and feed that status to Home Assistant to then perform actions. This can be used to, for example, automate killing the power if the radio gets stuck TX’ing when using automated digital modes software such as WSJT-X remotely. It can also measure the supply voltage, which is always useful information to know, especially when operating remotely.
This article contains information on how to calculate the operating margin of a wireless 802.11 network using a known distance between the two points.
I wrote this quite a while ago and although the throughput of wireless links has dramatically increased the basic theory still applies. Of course we now have 5GHz available, which is very useful for this application. You should be able to substitute ‘f’ for 5000MHz and the maths will still work.
You can now get a 150mbps PTP link over 15km using equipment that costs £160 for both ends – that’s the entire cost of the system (minus a couple of poles and brackets). Crazy value for money when you think about it. The Ubiquiti NSM5 NanoStation is one such example. The Ubiquiti product range is pretty impressive to say the least. The NSM5 seen below is the big brother of the LOCOM5, which at £125 can still do 10km at the same rate and are around half the size.
If you are considering an outdoor wireless link, give this article a read so you understand how high above objects you need to mount your shiny new kit!
Even having written many hundreds of Bash scripts over the years I sometimes forget the basic special parameters which are available. For that reason I’ve made this post which is a copy of the page from gnu.org.
If you have an APC UPS you may not, for whatever reason, want the OS to trigger a shutdown. The ‘apcupsd’ package will call shutdown whenever the battery capacity is reported too low. To prevent this, just edit the following file.
Here is a very simple way to download iPlayer content using a Linux command line tool. This literally downloads the stream and saves it to a file. The best part is, because they’re not DRM protected, you can keep it forever.