K7PEH: "Unless I have counted incorrectly this is the 20th topic posting on this forum since it was created in 2005. Wow, not much activity."
There's not much activity here on eHam but be assured that there is LOT of stuff going on in amateur radio circles. You just need to look in the right places for it:
http://www.hamsdr.com (~3800 members).
http://hpsdr.org/ (has active discussion forum).
These are some of the discussion forums on Yahoo.com:
SDR-IQ (~350 members).
soft_radio (~1050 members).
softrock40 (~2250 members).
The FlexRadio Systems webpage also has a link to a *very* active forum as well.
And finally this previously posted link is a very comprehensive list of what is all going on out there for SDR:
http://f4dan.free.fr/sdr_eng.htmlK7PEH: "What can SDR not do?"
Depends on its architecture is the simple answer. A broad generality is that the closer that the A to D sampling of the RF signal occurs then fewer restriction the SDR system will have. It will take more software obviously, but the overall limitations will be less. Obviously there will always be some hardware needed. And much of that will be manual controls should you need or even want them.
K7PEH: "Does DSP handle RF signals and if so where does it end, that is, at what frequencies (VHF ?) is the computer and software not fast enough."
For the last couple years the CPU power of the host PC is not the limiting factor of the PC based system. One of the neat things about the PC based approaches is that you can mix and match hardware and software to a pretty high degree quite easily. This is true even though much of the software is optimized for a particular piece of HW. There are two basic A to D / sampling approaches being commonly used today:
1. A relatively narrow (192 kHz or less) passband is sampled at up to 192 kHz and at either 16 or 24 bits. These are generally the PC sound card based systems.
2. A broad band approach that samples the entire HF spectrum at 65 MHz and 14 bits or so. These are the radio specific hardware based system that operate independently of the PC sound card, at least for the RX A to D sampling side of things.
They each have their own advantages and disadvantages. And there is also some degree of "blurring" between these descriptions of the two basic approaches.
I'm convinced that amateur radio SDR is as big or even bigger deal for the coming change in ham radio than either SSB or AM were in their day.