Good Morning Jim ... Thank you for the detailed measurements. That helps substantiate some of the word-of-mouth on the forum.
I have done no measurements, but do have a 400 Hz filter both in my main RX and in the sub. My main interest is CW contesting and I have found them more than adequate for everything except for conditions sometimes experienced in the 160 meter contests. On 160 the 200 Hz 5 pole filter in my main RX occasionally improves the situation with a very strong local station. But I agree with you that there is no need for the 250 Hz 8 pole option. 73 Craig AC0DS Craig D. Smith PowerSmith Consulting 1009 Alder Way Longmont, CO 80503 phone: 303-834-7712 email: [email protected] web: www.PowerSmithConsulting.com <> -----Original Message----- <> From: [email protected] [mailto:[email protected]] <> On Behalf Of Jim Brown <> Sent: Friday, July 16, 2010 12:48 AM <> To: Elecraft List <> Subject: [Elecraft] 250 Hz and 400 Hz Filter Measurements <> <> 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
