> It seems like Inrad may be using -3 dB for some of their > measurements. The corner of the bandpass is covered by the > data, but it looks very much like that 455 kHz 300 Hz filter > is 300 Hz wide at the -3 dB points.
Collins specified their mechanical filters at -3 dB. However, crystal filters in amateur literature have been specified at -6 dB for at least 30 years. "Shape factor" has been the ratio of -6 to -60 dB bandwidth for at least as long. 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Ron > D'Eau Claire > Sent: Friday, May 16, 2008 7:40 PM > To: [email protected] > Subject: RE: [Elecraft] RTTY Filter for K3 > > > One thing I don't see mentioned much - something that makes > ALL the difference in the world - is exactly *where* the > bandwidth is measured on the response curve. > > Years ago I saw a lot of bandwidth measured at the -10 dB > points (that was probably before many K3 owners were born - I > haven't seen it for a long time but it was pretty common at > one time). > > Then a *lot* of bandwidths were specified at the -3 dB or > "half power" points. > > Now -6 dB seems popular. > > It seems like Inrad may be using -3 dB for some of their > measurements. The corner of the bandpass is covered by the > data, but it looks very much like that 455 kHz 300 Hz filter > is 300 Hz wide at the -3 dB points. > > Ron AC7AC > > > > -----Original Message----- > > Ian, > > > In the intense QRM conditions of RTTY contesting in Europe, I > > routinely use two cascaded 250Hz filters at 8215kHz and > 455kHz in the > > 1000MP. (Unfortunately the new Inrad website doesn't > include filter > > plots, so it isn't possible to estimate the cumulative > bandwidths of > > these cascaded filters.) > > The "nasty little secret" is that all of the INRAD "250 Hz" > filters in the 8 - 9 MHz range have -6 dB bandwidths around > 325-375 Hz. That makes the original analysis accurate since > your FT-1000MP is really using cascaded 370/300 Hz filters. > > The old Inrad site is still available at www.qth.com/inrad > see the Yaesu "250" filters at: > www.qth.com/inrad/graphs/704.gif (455 KHz) > www.qth.com/inrad/graphs/708.gif (8125 KHz) > > 73, > > ... Joe, W4TV > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
