Sunday, October 02, 2011

G33DDC DDC Recordings

OK. About time to explore the functionality I missed in the G31. First a few words on on-the-fly recordings: This function works well but one should take care in activating the "Insert FDT" button as well as the "Split" button - the former to ensure you have frequency, date and time associated with the file, and the latter to avoid monstrous DDC files.(For the record: No, a 2 GB DDC file is not monstrous).

You can activate a buffer to make the recording start up to 3 seconds earlier. While the idea is very good, the limited buffer size makes it less useable than if you could select up to say 10 seconds.

Scheduled DDC recordings is an important factor because it adds flexibility to the DX hobby. A well designed scheduler is the key factor. This is how the Scheduler window looks like:
The jpg should be self-explanatory. What I'd like to add is that "Start time" is always the PC's local time, not UTC. Take care in selecting the correct DDC bandwidth (default is 24 kHz), and find a suitable argument for the Stop recording function.

The file is automatically frequency, date and time stamped. There is support for multiple tasks, especially suitable if you want to record different frequency spectra and other bandwidths

A scheduled recording is played back as shown below. If recording has been set up to split, the Scheduler will automatically start a new file linked to the previous one, and on playback will do so seamlessly.
Note that although the timer and the file name refers to the PC's local time, the date and time line to the left of the playback bar will display UTC, if UTC has been selected to be the primary time display (Options -> Time).

Sadly, the playback bar is still difficult to manouver. Inspiration for improvement could come from as different sources as Perseus, SpectraVue, SDR-Radio and Winrad. They are all much better.

G33DDC files will be huge. This is because unlike just about every other SDR on the market, the G33 makes 32-bit recordings up to 3 MHz bandwidth. The widest spectra (3.2 and 4 MHz) are recorded in 16 bit due to limited USB 2.0 transfer rate. Thus, 2 minutes, 40 seconds at 1.25 MHz will take up 2.2 GB. In comparison, the Perseus is 24-bit for all bandwidths except 1600 kHz (16-bit), while the netSDR is 24-bit up to 1 MHz and 16-bit on 2 MHz.

A 32-bit file contains more information than a 16- or 24-bit file. The question is of course if the added information can be used to hear more stations, like a considerably higher dynamic range, sharper selectivity etc. It would be nice if that was the case. Until someone comes up with proof I find it hard to believe that a G33 file recorded in 32 bits would let me hear more DX stations than a Perseus file recorded in 24 bits.


Chuck said...

Hi Bjarne:

Just so your reviews will have a 100% goodness factor, I'll point out that Perseus uses 16 bit values for recordings at 2 MSPS (1.6 MHZ).

Bjarne Mjelde said...

Thanks, Chuck. And since Perseus has no bandwidth between 800 (24-bit) and 1600, it's difficult to compare with the G33. I have corrected my post.