On Fri, 2006-11-10 at 14:19 -0500, michael taylor wrote: > :-) Silicon Labs makes one chipset used in some. It has a 8051 > microcontroller and a FM Tuner chip. I think all those chips output > Left/Right audio, not I/Q. > > http://www.silabs.com/tgwWebApp/public/web_content/products/Broadcast/Radio_Tuners/en/Si4700-01.htm > http://www.silabs.com/tgwWebApp/public/web_content/products/Microcontrollers/en/USBFMRadio.htm
According to the reference design (AN264), they are taking the analog out from the Si4700, putting it through a single pole 23 KHz lowpass analog filter, then using the 10-bit ADC on the 8051 to go back to digital. The samples over the USB are at 96 Ksps, 4 bytes each (two channels.) 10-bit audio doesn't sound fantastic but there is probably room for some DSP tricks to improve fidelity. They are oversampling by 3 since they are only starting with 15 KHz audio in the transmitted FM signal. AN264 refers to a reference design for Windows that implements the "over the USB" protocol for data and control. It probably wouldn't be all that difficult to hack up a GNU Radio driver that did the same, not that I'm volunteering. And each actual manufacturer may fiddle with the 8051 firmware to suit their tastes, so YMMV. On the other hand, these things are commodity priced ($30-$50 retail), so I'd bet they are barely repackaged reference designs with some cosmetic fluff wrapped around it, and no changes to the firmware. -- Johnathan Corgan, AE6HO Corgan Enterprises LLC [EMAIL PROTECTED] _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
