Why not just tighten the DSP on the 450 Hz filter instead of kicking in the 250 Hz filter? It's just as easy to do for when that occasional S9+30 signal pops up nearby, and at both 30db down and 60 db down you'd have exactly the same performance.
I happen to have the 250 Hz filter, but after seeing K9YC's data I'm convinced I would have been just as well off with the 400 Hz fllter (I don't see the need for both) and I would have saved myself 3db insertion loss to boot. 73, Dave AB7E On 7/16/2010 11:38 AM, Guy Olinger K2AV wrote: > In my radio I have the 400 set as 450 Hz, and I have the 250 set at > 350 Hz, well aware of how close they are. I use the 350 setting for > running when the stuff above or below starts to infringe and the > difference between the two. Pulling in the roofing filter against a > 9+30 signal just above or below is very noticeable and extremely > useful. > > Each to his own, just don't start a ban the 250 campaign. I know a > lot of contest operators using the 400/250 8 pole combo in the manner > I described. > > 73, Guy. > > On Fri, Jul 16, 2010 at 2:47 AM, Jim Brown<[email protected]> wrote: > >> Crew, >> >> I finally got around to dragging out my precision audio spectrum >> analzyer to check out the 250 Hz filters. I have two K3s, one >> with a single RX and one with two RS. I have 250 Hz and 400 Hz >> filters in all three RX. >> >> First, I tweaked the centering of each filter (that is, the >> offset), then I measured bandwidth at -6dB, -30dB, and -60dB with >> IF bandwidths of 1kHz and 250 Hz. >> >> Results: There was some variation from one filter to another, but >> trends are quite consistent. The only significant difference >> between the 250 and 400 Hz filters is at their -6dB points with a >> 1kHz IF, where the average bandwidths were 311 and 412 Hz >> respectively. This is essentially the bandwidth of the roofing >> filters themselves. >> >> Once you crank the IF down to 250Hz, there is no significant >> difference between the two filters. The average -6dB bandwidths >> were 193 and 200 Hz; at -30 dB, both filters averaged 300 Hz; at >> -60dB, they averaged 381 and 397 Hz respectively. >> >> There IS one repeatable difference between the 250Hz and 400Hz >> filters -- their insertion loss, which is 3dB. That is, the 250Hz >> filters have 3dB more insertion loss. >> >> After doing these measurements, I firmly agree with W4ZV, W0YK, >> and others, who have noted that there is no good reason for >> having both of these filters in a radio. Indeed, there is no good >> reason for the EXISTENCE of this particular 250 Hz filter, >> primarily because it is NOT a 250Hz filter by any reasonable >> measure. >> >> It is long past time for Inrad to lean on their filter supplier >> and get them to ship 250 Hz filters. Failing that, I want my >> money back for three filters. BTW -- all of these were purchased >> from Inrad, not Elecraft. >> >> 73, Jim Brown K9YC >> >> >> ______________________________________________________________ >> 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 > > ______________________________________________________________ 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
