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
