I thought some rigs also passed the transmit signal out past the filter, and to save money just fit say an FM sized filter there. FM and AM are 'features' also I guess...
The K3 is going to relay switch filters in for FM, AM, SSB, and CW. Since they are working at a lower frequency, they will really work well, and that is the main trick going on in the K3. Then you get all those DSP extra goodies... Brett N2DTS > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Larry Phipps > Sent: Thursday, May 03, 2007 9:12 PM > To: Jack Smith > Cc: Elecraft Discussion List > Subject: Re: [Elecraft] 8 pole vs 5 pole..I knew this would happen > > I think the term "roofing filter" is misleading. A narrow > filter at the > first IF protects a receiver even better than a "roofing filter", so > there is nothing inherently distortion reducing in using a > wider filter > at the first IF and then a narrower one later. The ideal > situation for > IMD would be a pair of matched narrow filters at both IFs. The real > reason for a "roofing filter" it seems to me, is to allow passband or > slope tuning. This compromises IMD and AGC performance for > the sake of a > feature... which may or may not be valuable to the user. > > Therefore, the "roofing filter" should be termed the "passband tuning > enabling filter", or "PBTE" filter ;-) > > Thankfully, I think Elecraft has done a brilliant job of > giving us the > options we want without compromises. By tying the DSP > bandwidths and PBT > functions to the "roofing filters", we have the ability to have the > combination of 1st and 2nd IF BW we want,,, and with the variable > "roofing filters", I think we will be able to almost set the relative > BWs between the two... allowing a window for PBT or not as we choose. > This is an exciting development, and will be copied by many companies > over the next year. Kudos to the design team on this. > > 73, > Larry N8LP > > _______________________________________________ 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
