> I recorded about 10 seconds of the ENTIRE FM band to a ramdisk, then turned around and pushed it back out in the unlicensed band on a continuous loop.
> Now I had a second problem on my hands: was it the recording itself? To answer that question, I took the file and washed it through a bunch more SDR gunk to isolate a single station, demodulate it to audio, and pushed it to my machine's speakers. The song sounded fine. Other stations were also okay.
Rachel, I would pay double-digit dollars per month for a screencast per week of you doing some serious hacker shit like this. (I've used Gnuradio et al and it's always a screaming pain, at least for a novice like me.) Watching someone hack away at it in a while(!functioning) would be pure pleasure, and I'm sure quite educational too.
I really enjoy reading these posts from Rachel. I think I have read like 10+ of them by now.
Can I be so bold as to suggest something for improved readability? [Edit: turns out I cannot. Immediate downvote!]
Breaking that wall-of-text into 2-3 sections with headlines would probably improve readability greatly. Honestly, it doesn't matter that much what the headlines say - the important thing is breaking up that wall of text into separate pieces.
> I recorded about 10 seconds of the ENTIRE FM band to a ramdisk
We live in wonderful age of SDR where this is not only possible but apparently also the way how even entry-level car infotainment's FM receiver works. And it still amazes me.
Depends on the box, but some years ago, I picked up an old slotted-Xeon server at a swap for a few bucks, and it had 32 DIMM slots on an enormous memory sub-board. Took registered or buffered ECC, as I recall. I scored a few modules on eBay and put 256MB into it, I think it would've gone to 4GB if I filled all the slots.
But the hard drives were SCSI SCA-2, which I believe maxed out at 40MB/s but in practice the drives were much slower. So yes, there was probably a point in time where a reasonably-beefy box would have had the specs you describe.
I think you have an extra factor of two there. If you need 20 MHz without aliasing, you either need real sampling at 40 MS/s or IQ sampling at 20 MS/s, but IQ sampling at 40 MS/s is overkill.
Nyquist works differently if your samples are complex.
I had a P3 desktop with a UDMA hard drive (33MB/s theoretical peak) and 128MB of RAM. A workstation of the time would have over 512MB of RAM and a SCSI drive that might not sustain 40MB/s.
Going back further, in 1995, a SPARCstation 20 had a SCSI-2 controller (10MB/s maximum transfer rate) and could be fitted with 512MB of RAM.
I mean SATA 3 has a bit more than 500MB/s right, and PCIe SSDs run at between 1-4 GB/s? so a machine today (at least 8GB of RAM maybe in the hundreds) would have an even bigger ratio between memory size and disk transfer speed.
> Now I had a second problem on my hands: was it the recording itself? To answer that question, I took the file and washed it through a bunch more SDR gunk to isolate a single station, demodulate it to audio, and pushed it to my machine's speakers. The song sounded fine. Other stations were also okay.
Rachel, I would pay double-digit dollars per month for a screencast per week of you doing some serious hacker shit like this. (I've used Gnuradio et al and it's always a screaming pain, at least for a novice like me.) Watching someone hack away at it in a while(!functioning) would be pure pleasure, and I'm sure quite educational too.