> These measurements are QUITE valid, and represent the response of the > radio > from antenna input to audio output. The wide and narrow measurements on > the > same page are the same data, plotted to different scale -- the narrow > plots > to show filter bandwidth, the wide plots to show behavior well down the > slope of the filter curve. The dynamic range of the measurement is at > least > 75dB.
I'm still mulling this over but........the curves of the "filter response" are very similar to the output distribution I've seen when I was using a multiple carriers to measure IMD in CATV amplifiers. The problem is that was over 30 years ago, so my recall might be flawed. I'm having a little trouble understanding how the equivalent of an infinite number of carriers in a passband can be used to measure filter shape when the distortion in every stage after the filter can cause mixing and produce intermodulation products outside the filter passband. If I wanted to know the deeper attenuation response of a filter or system with a filter, I would use an input signal that would not fill the system after the filter with multiple frequencies (that are unattenuated since they are inside filter passband) that could mix and display intermodulation products. I think there is significant risk using broadband noise through the filter might display intermodulation distribution more than filter skirt response. My inclination would be to turn off the AGC and sweep with a single tone. I'm not so sure a measurement like this isn't just a measurement of odd-order IMD in stages following the filter. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
