This post has been stuck in draft for a while now because of the lack of VHF/UHF amateur activity in my area. After changing the title and doing a rewrite, I gave up using my own radios and turned to the world of online SDR to give my the signals needed (and even then it was no cakewalk).
Note : I have moved location now but this post is so far from the original that to go back would mean another rewrite (which isn’t going to happen, I’d rather save any new materiel for a fresh post or two).
Instead of feeding the audio from a separate receiver into the computer, I took it from the computer itself and passed it into the decoder. This basically means that whatever sound your computer is hearing (and giving to you) is what a program like MultiPSK has to work with.
The does need some messing around with the sound options and you’ll need ‘Stereo Mix’ enabled in your recording control panel (Windows operating systems).
Unfortunately and even a little bizarre, this option isn’t a given on Windows operating systems and if its not there, you’ll have to mess around in the registry.
Not every bodies cup of tea and potentially fatal if you get it wrong but there’s some great step by step instructions on video sites like YouTube for you to follow.
As stated above this can cause problems if not done right and if your not overly confident then you could always run a 3.mm audio lead from you computers headphone socket back into the microphone input (a little messy, but some playing with the levels can give good results).
Setting the Volume
You can do this a few ways but I find whacking the recording volume of the stereo mix right up then using the volume on the WebSDR receiver for control. One drawback of this way is the fright you’ll get if another piece of software on your PC decides to burst into life with a notification or two 🙂
Any sound thrown into the mix will also end up on the input to the decoder and mess with a clear decode, so its a good idea to keep these interruptions to a minimum anyway.
The other reason to close all unnecessary programs is to prevent audio from the WebSDR interface “glitching” and resulting in breaks in the audio (and decode errors).
If your lucky enough to have a great broadband connection and the sort of computer that will take everything you throw at it, then this may not be something you’ll ever have to worry about.
There’s a abundance of amateur radio data transmissions around the HF bands and you won’t have to do much searching to find something to decode (no matter what time of day you go looking), the same sort of signals at VHF/UHF are a little harder to find.
Its not that people aren’t using data modes on the higher ham frequencies, its just that the behavior of radio transmissions (line of sight etc) on these bands makes hearing them more difficult.
By using a few WebSDR receivers at least you’ll get a good shot at trying different locations around the world with the ability to tune into a timezone with peak activity, regardless of what your local time is.
As a majority of WebSDR’s are based around ham radio frequencies you’ll have no shortage of places to listen. Going for a receiver located in a heavily populated area will increase you chances of finding something useful, obviously 🙂
Given the right day and time (Sunday afternoons are normally good) you should be able to find modes like RTTY, PSK etc and if your very lucky, some SSTV to decode.