On Wed, Dec 3, 2008 at 12:55 AM, Joe Subich, W4TV <[EMAIL PROTECTED]> wrote:
>.> You are making the incorrect assumption that we have no >> control over the upper or lower limits. If band or sky noise >> is the limiting factor on the low end, then adding >> attenuation in front of the ADC to adjust for this has the >> benefit of increasing the high end limit also. This ideally >> has not changed the dynamic range, but only shifted the upper >> and lower limits. > No, if band noise at -110 dBm is the limiting factor as it > often is below 5 MHz, no amount of attenuation is going to > allow you to resolve a - 125 dBm signal. Attenuation may > help you handle blocking signals, particularly those 20 to > 100 KHz away that are eliminated by the narrow filtering > in other receiver designs and thus deal with the "window > overload" issues but that's all that moving the "IMD range" > can accomplish. Where in my statement above did I say that attenuation is going to help you receive a -125 dBm signal when the band noise is at -110 dBm? You won't be able to do that with a K3 or a SDR. I don't know where you got this idea. I was responding to your claim that we had no control over the lower input limit to the ADC and somehow that would limit BDR. We do have control over the lower input limit via attenuation (or gain). >> The Perseus or QS1R will easily outperform the K3 in the case >> of multiple strong signals in discerning a weak signal as you >> have described. This is WITHOUT AGC in front of the ADC. > > I do not believe that any wideband SDR can cope with the > instantaneous peaks greater than the ADC rail in the > limiting condition (a large number of extremely strong, > say greater than -10 dBm, within the bandpass filter > "window."). While the chance of the instantaneous maximum > decreases as the number of signals increases, the average > signal level continues to increase at an exponential rate. > > 73, > > ... Joe, W4TV I can tell you that QS1R can handle multiple 0 dBm signals in or outside of the bandpass filter "window", whether you believe it or not is up to you. If you exceed the clipping limit ( +9 dBm with no attenuation in QS1R) then that's it - but that is true for the K3's ADC also. -- Phil Covington Software Radio Laboratory LLC Columbus, Ohio http://www.srl-llc.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
