Yes, and you'll need to synchronise with the bit-stream somehow. Do you have a reference for how the signal is encoded? Sounds like an interesting project -- do let us know how you get on!
The digital data rate is very slow, 25bits/s , so I will have no problem using an Arduino to synchronise with the bits and to decode the message providing I can get something that gives me an analogue signal showing the phase shift of the carrier.
Full details of the radio signal can be found here http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf, the key information is figure 2 "Phase of data modulated carrier as a function of time". It is quite simple to understand;
- A ‘1’ is represented by the carrier signal phase changing from a phase advance (+22.5 deg) to a phase retard (-22.5 deg).
- A ‘0’ is represented by the carrier signal phase changing from a phase retard (-22.5 deg) to a phase advance (+22.5 deg).
- td is 40ms.
I need off-the-peg hardware that gives the analogue signal shown in the figure.
That is where I was hoping the forum could help. Basically I am looking for a shield that acts as a LW radio receiver and provides an analogue reading of the phase shift of the carrier. I know there are shields that act as radio receivers that can be controlled by an Arduino, allowing bands to be searched and so on, and which provide information such as signal strength – but I have not been able to find any that provide phase shift information.
You need a phase locked loop to do this, google it for details. You can get a complete phase locked loop in a chip one such is the 4046.
The 4046 might well do the job, but for me to be able to use it would need to be on a shield along with the LW radio receiver circuitry. I am hoping somebody will know of existing hardware that will do the job.
I'd have thought that sort of frequency [198kHz] far too high for submerged reception. Perhaps somewhere around 16kHz might be a more realistic figure.
Sorry to spoil the Conspiracy Theory but BBC Radio 4 on 198kHz is not used by Nuclear Subs. They can communicate submerged using Very Low Frequency (VLF) [3-30kz] and Extremely Low Frequency (ELF) radio. So jackrae was right in the middle of theVLF band. This article http://en.wikipedia.org/wiki/Very_low_frequency suggests VLF signals can be received using a PC - but that is a whole other project.