Tuesday, November 9, 2010

Receiver DReaMer

Brendan is a longtime DRMNA member and DRM enthusiast. Brendan and I connected mentally from our first emails a few years back. We both love radio, have some practical knowledge from our years of experimenting, but lack expertise in programming and rubber-meets-the-road circuit building. Based on a post of his and a rebuttal from another longtime DRMNA member Mark, here is bit from Brendan on what he would like to see in our DRM receiver.

Since the idea of an open source DRM receiver has proven irresistible, I decided to take a crack at it. Please note, I am neither an RF engineer nor a computer programmer, so any errors or omissions are done in sheer ignorance. I am enthusiastic however, and that should make up for any other shortcomings.

In reviewing the idea of such a receiver, some questions came to mind as to what specifically we would be creating: a DRM radio for all, or parts of one, or something simpler? In putting my first thoughts to the DRMNA list, Mark countered with the idea of designing a decoding module alone, one that would do all the processing necessary to decode a DRM signal without resorting to a PC.

Essentially a pre-programmed CPU in a box with audio output, the user would only need to tap the IF of any radio and be able to receive DRM once that is done. I would add that if we take this route that the decoder be able to utilize any IF frequency that the user's radio may have: 12 KHz, 455 kHz, or even Icom radios at 9.0xxx MHz. Whether this is through easily swapped components or modules, or within the software, this feature alone would be very useful. Starting with this aspect of the project would be a good start to completing the entire radio.

My own ideas began with questions about what type of receiver are we talking about? A battery operated, stand-alone DRM/AM/SSB/CW/FM receiver with all the bells and whistles, or just a DRM only receiver with fixed channel reception based on the internet DRM schedule? By the way, the Uniwave receiver has a small, free PC program that downloads the same schedule we all use in Dream and then further allows the user to easily modify the stations in the listing: here in North America we really don't need the long or mediumwave stations from Europe and they can easily be deleted.

I also was thinking that what if these two radios are one and the same, essentially taking the simpler radio and adding modules to expand its operating controls and flexibility. Options such as built-in recording, full keyboard frequency entry, extension into the FM band: those options are limitless. I believe that a Software Defined Radio (SDR) is the way to go for the radio front end. They are now becoming very simple to design, very cheap to build, and very small in size. Given the inherent flexibility of an SDR, this is all we really need.

After the radio, what is left is the "back end," the processing CPU to decode the OFDM signal of DRM. Alan originally proposed doing this with an 'Arduino' processor package, while Mark Phillips has suggested a 'dsPIC' chip as being more powerful and able to do the heavy lifting involved with decoding DRM. I shall bow to Mark's professional knowledge in this, I have no reason not to. I do know PIC's are very widespread now, and easily worked with. Lastly, none of this hardware will work without software.

Is the Dream package able to be used in a stripped down form inside our "back end?" Or do we have to do some re-coding to make a finished product? My knowledge in this area is very lacking, and any comments would be highly appreciated. The Dream software would fit on a very small capacity SD or Micro SD card, and so would any of the other files it needs. We certainly don't need all the functionality of Dream, just the major one of decoding. Anything else would be just cream in the coffee.

Wish-list items: a form of USB interface would be good for updating frequencies and operating software, even perhaps for downloading log file data. Another idea would be to develop an 'on-air' schedule update that broadcasters themselves could send over the data stream available in DRM. For listeners and users without a PC, this would be extremely useful, especially if done automatically.

These are simply my thoughts on the whole open-source radio project. Please post your comments on the DRMNA Yahoo Group. We need input, and with all the enthusiasts, pros, and innovators in this group we can certainly come with a do-able radio. A name? "Dreamer 1.0?" "Open Radio?"