Richard, You were not hearing the effect of the 2.8 MHz roofing filter, but instead the DSP filter. In order to hear the effect of the 2.8 kHz filter skirt, you would have to widen out the DSP bandwidth to max or greater. The DSP forms the ultimate filter, and does have nearly vertical slope.
The purpose of the roofing filter is to keep adjacent strong signals from activating the hardware AGC and causing the resulting AGC pumping. It is the DSP that sets the actual filter width. 73, Don W3FPR On 7/12/2011 2:22 PM, Richard Fjeld wrote: > FYI, > I don't want to open up a 'can of worms', and Rob Sherwood could better speak > to this, but this is an observation I made using a P-3. > > Not long ago, there was quite a string of threads about the 5 pole 2.7 Khz > roofing filter versus the 8 pole 2.8 Khz filter. Before I ordered my K-3, I > had studied the filter skirts of each. I don't remember how I found the plot > for the 5 pole filter, but I remember that the span of each was different. At > the same span width, the 2.8 Khz filter skirts seemed to me to be > considerably straighter when compared to the 2.7 Khz filter, so I ordered the > 2.8 filter. > > The other day, I was on a qso with a group and while watching the SSB signal > on the P-3, I noticed a carrier much taller appear right on the edge of the > filter bandwidth as shown by the brackets at the bottom of the P-3. The > carrier was on the far end of the filter, or 2.8 Khz away from the center > frequency. > > I could not hear it, but expected to, so I tuned over slightly to get it > within the filter bandwidth and heard it strongly. I seem to recall that a > filter's width is rated at something like 6 dB down, so I thought I would > have heard it within the skirts at their wider limits. I still wonder about > that, but I'm very pleased. > > (Just a comment; I'd hate to do without the P-3) > > > Richard Fjeld, n0ce > ______________________________________________________________ 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
