New project– BATC DigiLite DVB-S Modulator
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.
How is your DigiLite project coming along ?
I’m thinking about ordering that board from BATC.
Were North of Columbus Ohio . Here is my home page.
Our Google ATV map
I’ll update it in a few days. I have all the parts on the board now except for the AD8346. I probably will order another “Israeli” PLL oscillator as I am not sure if I want to tear apart the one I bought a couple of years ago for a 1152 MHz source. And then there is also the PA portion. Later on that.
If there is ongoing interest in the US, I think we should consider a US version of this board… if it’s “OK” with the BATC to do so. There are several minor changes I’d do to the board, such as eliminating all but one of the expensive chip tantalums (one is needed for the DSPic’s internal regulator)– but 1/4 of the parts cost is those stupid bypass caps, going to leaded 10 turn pots, and maybe even building the PLL synth on the board.
I’ll likely post a new blog post after I get the AD8346 on the board.
But, go ahead and get the board and the balun at the very least from the BATC. I also bought the pre-programmed PIC, but I found that I can (with a major hack) program the DSPic’s also. Let me know if you need one programmed. If so it might be easier to order that from the BATC also. I’d get the oscillator board right from Israel on e-bay and the FT-2232H mini module from Mouser tho.
I powered up the board last night, verified the voltage regulators were regulating and inserted the DSPic that I programmed (I also bought one preprogrammed).. the LED blinked as it should. So I’m getting closer.
I also now have the modulator IC AD8346.. so very soon I should have the project working..