Flex implements the AGC in software so it can be finely controlled and maintain accuracy of the input signals.
With SDR the philosophy being that as much as possible to be moved from fixed hardware to a DSP, PC, or FPGA so it can be controlled and changed by software. The second you put in a traditional AGC then you have no clue of the system gain and your S-Meter is no more accurate than your typical receiver where it's basically and approximation of signal strength. Also to be noted on a SDR radio the largest signal in the band-pass, not the one you are listening to must not be allowed to saturate the ADC's with hardware that is difficult do, with software it's simple, you look through the FFT bins for the largest signal and set the receiver gain accordingly. The SoftRocks series is meant to demonstrate how simple the hardware needs to be to create a quality receiver. All the "traditional things like AGC, Filtering, Demodulating, and Noise reduction is carried out in software not in hardware. But to keep them inexpensive Tony had to use a fixed crystal frequency, and do not they have a front end pre-amp, and that is the main limit of them. Within their range and limits they work remarkably well for such simple piece of hardware again demonstrating how most of the hardware feature can be moved to the software side and they should so you have more control over the radio. As little hardware as possible, and as much software as possible is what makes a SDR radio a superior and extremely adaptable radio. Because a QSD mixer is so clean, the LO becomes a critical part( it's always been in any radio) of the radio, and the individuals who pursue creating variable clean LO's will be rewarded with a high performance in the little radios. At 11:32 PM 6/12/2006, you wrote: >Francis Carcia: > > Yes there is that problem of agc acting on all of the spectrum > coming into the sound card over 96 kHz. So I propose that as a > standard when desired to be use that any agc applied needs to be > both switcable on and off and also adjustable. Even adjustable in > time constant which mere capacitors can accomplish. > > My first view of agc was to sample the output from the sound card > of the desired signal level and use that. A better idea then, to > use the audio output of the sound card to control itself going into > the final audio amplifier section external to the PC in the monitor > system. This way only the desired audio will have agc applied. > > Sometimes however it might be desirable to have some agc in the > receiver and so as I mentioned above that can be switchable. Again > the better idea for that is to use only the sound cards output as > the signal that controls the receiver as well as the external monitor gain. > >ka9rza > > >_____________________________________________________________________ >Call Anyone, Anytime, Anywhere in the World - FREE! >Free Internet calling from NetZero Voice >Visit http://www.netzerovoice.com today! > > > > > > >Yahoo! Groups Links > > > > Cecil Bayona KD5NWA www.qrpradio.com "Windows, the most successful software virus ever" Don Seglio Batuna ------------------------ Yahoo! Groups Sponsor --------------------~--> Protect your PC from spy ware with award winning anti spy technology. It's free. http://us.click.yahoo.com/97bhrC/LGxNAA/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/
