Hi Chris, Thanks for your polyphase filter references. I'll have to look at it in more detail. Is it used only for SSB demodulation?
Right now, I am contenting myself with starting up one rig to cover 10Mhz to 29.9Mhz properly bandpassed and hooking the QSD to a PC sound card with in parallel a speaker and a PIC. On a sound card, a very aggressive low pass filter is built in the codec before the 24bit quantization. My question is that if I don't use a computer, what kinds of low pass filters have people used and what are efficient approaches to this? I expect to run into problems of interferers stronger than a desired channel frequency that will get amplified and force some audio stages to hit the Vcc and ground rails. I presume it will not be bad on an audio speaker if I keep the volume low and get the adjacents at frequencies above the human hearing threshold. Unlike the PC sound card's codec a PIC's ADC would need to be protected. What can I use besides cascading multiple 2nd order op amp low pass filter circuits? Frank P.S. I took a look at your main block diagram on the yahoo site. Do you use the PowerSDR from flex-radio or something else right after the INA163? Does SCAF stand for switched capacitor audio filter? On 13-Sep-05, at 5:10 PM, [email protected] wrote: > Hi Frank > > I think You mean not a LPF, but a Polyphase Network (Allpass Filter). > > For SSB demodulation You take the I and Q channel from the QSD and > turn one channel about 90°. Then You adding the channels and the > result is USB. Or You subtract and the result is LSB. > Many types of this filter turn both channels about 45° and the result > is the same. > > In my HDR-2005 I use an active filter with 4 Dual-OPs (look at > soft_radio/Files/HDR-2005). If You want, I send You a detailed > schematic. My troubles with demodulation are not SSB (it sounds very > good) but AM, You know ;-) > > Chris ------------------------ Yahoo! Groups Sponsor --------------------~--> Get fast access to your favorite Yahoo! Groups. Make Yahoo! your home page http://us.click.yahoo.com/dpRU5A/wUILAA/yQLSAA/ELTolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
