OK, that brings me back to the original question ... since the standard 2.7 KHz, 5-pole filter is 2900 Hz at -6dB which should be wide enough on receive for AM (by shifting the receive passband to use one sideband) and for ESSB (except for the ultra fidelity group), is there any harm in using the FM filter for AM and ESSB transmit?
If one wants maximum performance on AM/ESSB receive, I understand the 6 KHz filter will provide better IF image rejection (now I'm really interested in the FM filter curves - including the stopband and ultimate rejection specification). However, if the priorities are maximum performance on SSB and CW (including protection from AGC pumping), a slight (?) reduction image rejection due to the wider filter may be an acceptable compromise given the limited number of available filer "slots". What is the ultimate rejection in the 8-pole filters, the on-line curves only go to -80 dB? Some of the filters (250, 400, 1.8K) show signs of "flaring out" at 70 to 75 dB down and for others (6K, 2.8K) the scale is wide enough that the skirts are "off screen" before they reach -80 dB. Of course, this may all be academic when variable width filters are available. 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Lyle Johnson > Sent: Wednesday, October 24, 2007 11:32 PM > To: [email protected] > Subject: Re: [Elecraft] [K3] Unanswered Questions ... > > > >> In FM mode, capture effect helps suppress the effect of "image" > >> leakage. AM and (E)SSB modes have far more dynamic range and the > >> 15 kHz IF image must be suppressed by some 10s of dB more than is > >> required for excellent FM operation. > > > > Are you speaking of receive performance or transmit performance? > > Receive characteristics. > > > ... > > Is there something in the digital domain that I'm missing - > > aliasing, artifacts, etc. that effects this? > > No, the issue is IF image rejection. > > 73, > > Lyle KK7P _______________________________________________ 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
