The most comprehensive writeup I've seen is here: http://www.elecraft.com/K3/Roofing_Filters.htm
I'd agree that you probably don't want to order 200, 250, 400 and 500. However two of these four makes sense for some buyers, including me. If you configure the radio correctly, roofing filters are selected automatically as you turn the "width" knob. You may also directly select a roofing filter. I just twist the width knob to adjust the DSP bandwidth and the appropriate roofing filter is selected for me. One "reasonable" starting configuration is just the stock 2.7 KHz filter. If you want to transmit AM, you'll need the 6.0 KHz AM filter. If FM is important to you, you'll need the FM filter. I'm not currently interested in transmitting in either of these modes, so I skipped those two filters and I can receive AM with adequate (for me) fidelity by using my 2.8 KHz filter and listening to one sideband. Discerning AM buffs might well have a different definition of "adequate fidelity". If you're interested in CW or "data" modes (RTTY, PSK, etc), then you'll perhaps want to invest in one or more narrower filters, perhaps one or two of 200, 250, 400, 500 Hz. If it's only one narrower filter, I'd suggest either the 400 or 500 Hz filter. I think of the 200 and 250 as alternatives and 400 and 500 as alternatives. I wouldn't think you'd want both 200 and 250 nor would you probably want both 400 and 500. I personally don't think the difference between the 2.7 and 2.8 Hz filters matters much, but I did choose all 8-pole filters. As a result I have slightly wider SSB transmit bandwidth and sharper skirts on receive with the 2.8 KHz 8-pole filter. I like the 1.0 KHz filter as a "normal" CW bandwidth in contest situations. It's not so tight that I can't hear off-frequency callers. The 1.8 KHz filter is a wonderful filter for phone contests and other shoulder-to-shoulder situations on phone. Others prefer 2.1 KHz for their narrowest SSB roofing filter. With the 1.8 I find that the off-frequency crud often disappears, and the signal I'm isolating is comprehensible, but "communications" fidelity rather than natural sounding. I have to defer to the RTTY and PSK experts, but I think a 400 or 500 Hz filter would be my 2nd filter (after the 2.7 or 2.8 decision). My experience before the Elecraft K3 was with a series of up-converting ICOM rigs including the 7800, whose narrowest roofing filter (after the roofing filter upgrade) is 3 KHz. I chose 8-pole filters at 2.8, 1.8, 1.0, 400, and 250. I probably have more than I need for almost all situations. Most of my QSOs don't tax the capability of any current-generation radio, but when the situation is very competitive I don't want to be in mid-contest or mid-pileup and at that time wish I'd spent the relatively small amount (compared to all the other expenses in building a station) that these filters cost. You don't have to decide all this at the time you receive the radio. You can add roofing filters easily at a later date. You just have to remove a handful of screws (top cover and half the bottom cover), and the filter plugs in and is held in place by one lock washer and nut. You might need to rearrange your existing filters when you add a new one so that they're in a natural sequence. Filter configuration takes a few minutes after you get the hang of it, and it'll be even quicker with the next revision of the K3 Utility. If you decide to add the 2nd receiver option, you'll need filter(s) for that receiver as well. You might make the same decisions again or maybe not. I'm going to make different choices for my 2nd receiver. Sorry it's not a crisp answer. It's like a lot of topics, the answer is always "it depends"... 73 de Dick, K6KR -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim Miller Sent: Monday, March 31, 2008 8:59 PM To: Elecraft Reflector Subject: [Elecraft] K3 Filter Configurations and Explanations Thanks for bringing up the filter topic - This is one of my main questions now. I finally ordered mine with no optional filters and plan on adding them to the order before ship BUT I do not know which will be the best for me. I suppose the answer to that is that it will be different for everybody. I do expect to add the second reciever board at some point, maybe not before initial ship. Some sub-topics: 1) Is there any point in ordering the 200, 250, 400 and 500? Probably not. Somebody explain how the filters are selected by the radio and recommend a couple of reasonable configurations please. I want to be able to run PSK, RTTY, CW and SSB and mainly I want to not have to deal with nearby signals, I want them GONE. 2) a. Why would you order a 2.8 when you get a 2.7 with the radio? b. Can you order the 2.8 instead of the standard 2.7 and receive "some" credit for the 2.7 you didn't want? 3) Will the 1.8 make the SSB hard to understand vs possibly the 2.1? I almost ordered the 1.8 but wasn't sure so didn't order anything yet. 4) What would be the best filter for RTTY? 5) Which filter will be best for PSK? A 6K filter or a 2.8 or narrower looking at just part of the band at a time? Pick one (or all) and give me your thoughts, THANKS, de Jim KG0KP (NewBee) _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
