Note: a longer and more technically detailed version of this is at my other 'blog, which I've decided not to syndicate.
Why was I up to 3 AM last night, making me miss the Iowa QSO party today? I received a care package via “Royal Mail” on Friday from the British Amateur Television Club. It is something that was designed almost the same way (actually more clever in many respects) that I had been thinking of doing for close to 10 years.
The DigiLite is based on the “Poor Man’s DATV” by F4DAY. The project has been updated for modern computers by using a 2 channel FTDI USB serial port chip (which is the “why didn’t I think of it?” part of the design) and a closed-source (unfortunately) DSPic33 and Windows PC software to capture data from a “e-bay special” several year old Hauppage PVR-150, 250, 350 (and probably PVR-USB2) analog capture card from e-bay. (What is special about them for this project is an Conexant MPEG-2 encoder hardware chip and they are cheap!)
The BATC’s solution of using an inexpensive PIC and the FTDI serial interface is a maybe slightly kludgy but awfully clever solution of inexpensively and simply pumping data to the QPSK modulator chip. Although there are some disadvantages to this simple interface, it is an awesome start!
The modulation used is DVB-S, which is the older digital standard used by most of the world for satellite transmissions.
I’ve been playing with LEGAL Free-To-Air satellite for many years. The majority of what is left unencrypted on C-band and Ku-band FSS satellite is receivable on an inexpensive set type box and/or PC receiver card. These receivers take in 950-2150 MHz signals as an IF (with a converter and/or a LNA in front of the IF) in Amateur use.
The main disadvantage to DVB-S for ham radio is that the modulation is pretty weak when it comes to handling multipath. Existing Yagi beams other directional antennas will mitigate this greatly in Amateur Use. See the other ‘blog for details.
THE great advantage to DVB-S for ham use– in my opinion– is that the bandwidth and data rates, even the video and audio coding the the MPEG-2 Transport streams are pretty much completely up to the link user. DVB-T in Europe and ATSC in the US is only setup for 6/8 MHz channels and IMHO there is no reason for hams to use this much bandwidth in 2011 for ATV. Neither are a good choice for low bandwidths as we NEED to have in amateur television.
Experiments by the BATC and others show that the digital signal is much more usable and stable than equivalent bandwidth analog ATV and it just gets better with reduced bit rates.
Ho, Hum? ATV? who cares? Well.. see.. it’s not really just that, is it? Data such as DVB-IP can be used for data instead. There are $20 e-bay DVB-S cards capable of receiving data as a native computer network interface via this protocol. Maybe we can restart a packet radio network up again?
So this is the start of an interesting project for me that I’ve wanted to do forever. Hopefully it will turn out well and can be revolutionary.