> I would disagree regarding the value or benefit of the 1 KHz > filter. Originally I had, for CW, 1800, 500 & 200 filters. > Since I normally set the width to 700 Hz for normal non > contest CW operating, it seemed that I was having problems > with loud signals within about 900 to 1800 HZ hitting the > AGC. So when a 1000 HZ filter became available to trade for > my 1800 HZ filter I jumped on it and have not looked back!
As I responded to someone who raised this same point privately, the wider filters are not centered on the desired signal. Thus, if you favor a pitch of 500 Hz the 1000 Hz filter provides a "window" that runs from approximately 600 Hz BELOW the desired signal to about 400 Hz ABOVE the desired signal. The 1500 or 1800 Hz filter simply extends the window DOWN. With the asymmetric "window," if one is receiving QRM on the "wide" side changing to CW REV is just as effective in eliminating that QRM as switching to a narrower filter. If switching to the opposite sideband results in QRM from other signals, one would need to use a still narrower filter - e.g., 500 Hz - to eliminate the QRM from both sides in any case. Because of the asymmetric window, there is little performance difference among the 1000, 1500, 1800 and 2100 Hz filters in CW. Nobody has bothered to report the fact that 2 KHz IMD with the 2.7 or 2.8 KHz roofing filters is DIFFERENT if you measure above and below the interfering tones ... this is due entirely to the asymmetric window. The same differences will be observed with 1 KHz or 500 Hz IMD DR in CW with any filter wider than 500 Hz. There is no doubt that an 800 Hz filter would be a good option for "wide" CW or that the 1000/1500/1800 Hz filters might have some benefit if the IF DSP were modified for "single signal" operation and the filters "centered" on the desired CW signal. > Last year in CQ WW CW I have had a chance to sit down on 20 > meters with a K3 with 400 & 250 HZ filters. I was very happy > to switch radios back to my K3 with 1000, 500 and 200 HZ filters. The 500/400/250/200 Hz filters have been discussed at length. With real bandwidths of 480 Hz (measured in four filters in my K3s) for the 500 Hz 5-pole filter, 450 Hz for the 400 Hz filter (Inrad web site), 350 Hz for the "250 Hz" filter (Elecraft web site) and 205 Hz for the 200 Hz filter, my choice will be to move from the 500/200 Hz combination to the 400/200 Hz pairing. The added skirts will improve performance where the wider filter is useful (particularly RTTY) without being significantly more narrow than the current 500 Hz 5-pole filters and the 200 Hz filter is the best truly narrow option. 73, ... Joe, W4TV > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of .k8dd. > Sent: Wednesday, April 15, 2009 12:10 AM > To: [email protected] > Subject: Re: [Elecraft] Filter Selection Approach > > > > > > > That is a lot of filters ... > > 2) Unless you are in very heavy QRM/pile-up situations the > roofing filter does not provide a lot of "value added" > since the final bandwidth is determined by the DSP. The > 1 KHz filters add little benefit vs. the 1.8 KHz or 1.5 > KHz filters. > > > > I would disagree regarding the value or benefit of the 1 KHz > filter. Originally I had, for CW, 1800, 500 & 200 filters. > Since I normally set the width to 700 Hz for normal non > contest CW operating, it seemed that I was having problems > with loud signals within about 900 to 1800 HZ hitting the > AGC. So when a 1000 HZ filter became available to trade for > my 1800 HZ filter I jumped on it and have not looked back! > Last year in CQ WW CW I have had a chance to sit down on 20 > meters with a K3 with 400 & 250 HZ filters. I was very happy > to switch radios back to my K3 with 1000, 500 and 200 HZ filters. > To my ears the 500 & 200 filters were a definite advantage > sorting out the weaker European signals in between the loud > east coast U.S. stations. This was not at all a scientific > test - just how it sounded to me! > Both K3s were using the same firmware. > And I really think if I had purchased a K3 with no roofing > filters, like I've seen suggested, I would have most likely > sold the K3 and gone back to a K2! Just my thoughts. > 73 Hank K8DD > -- > View this message in context: > http://n2.nabble.com/Filter-Selection-Approach-tp2630347p2636834.html > Sent from the Elecraft mailing list archive at Nabble.com. > > ______________________________________________________________ > 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 ______________________________________________________________ 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
