> - For RTTY, my default bandwidth is 200Hz plus the Dual-Tone > Filter of additional cascaded 50Hz filters around each tone. > In theory, the bandwidth for 170Hz-shift RTTY should be > 250-300Hz, but I've found operationally that 200Hz works > great in my RTTY contesting.
The two 50 Hz filters spaced 170 Hz would have a total bandwidth of 230Hz. This is very close to the "published" value of 224 Hz for the 5-pole filter (I intend to measure mine when it arrives later this week). However, I wonder if it would not be useful to modify the 200 Hz filter - or for Elecraft to offer a "real" 250 Hz filter using the values shown in the K3 schematic pack (page 7). Based on the published 224 Hz (and reports of 210 Hz) and 4:1 shape factor a "250 Hz" 5-pole filter would still offer much better performance between -6dB and - 30 dB than the "250 Hz 8 pole" filter but a "real" 250 Hz wide filter should be just enough wider to eliminate potential "sharpening" of the dual- tone (DSP) filter. My filter choices - and I'll see if I guessed right in a week or so - were FM, 2.8 KHz, 500 Hz and 200 Hz. I'm leaving the one slot open for 2.1, 1.8 or possibly a variable SSB filter if/when that is available. The FM filter was chosen for general non-critical listening (including AM) as it is still narrower than the front end filter in any of the mid-grade "up-conversion" receivers. I know I will want something "between" 2.8 and 500 Hz and suspect the 1.8 will fill the bill for general CW on a quiet band and for "click on the waterfall" PSK31 operation. 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Ed Muns > Sent: Tuesday, April 01, 2008 2:33 PM > To: 'Jim Miller' > Cc: 'Elecraft Reflector' > Subject: RE: [Elecraft] K3 Filter Configurations and Explanations > > > Repeating what I've posted here previously, the first thing > to get firmly in mind about the K3 crystal filters is what > their purpose is. They are not used to determine the > bandwidth you are using on any mode. (Yes, you need the 2.7 > or 2.8 for transmit on CW, RTTY and SSB. The AM and FM > filters for transmit on those modes.) Your receive bandwidth > is determined by the DSP filtering which is continually > adjustable to any bandwidth you desire. The Icom 756Pro > series radios are excellent performers and have a single > 15kHz crystal filter. Narrower filtering is provided by the > DSP just like the K3. > > The purpose of the five easily-installable crystal filters in > the K3 are to pre-filter strong nearby signals so that the > DSP can better do its excellent job of the primary filtering. > INRAD makes add-on "roofing filter" kits for many radios and > now has a 4-5kHz "roofing filter" kit for the Icom 756Pro > series for those people who are mostly interested in CW, RTTY > and/or SSB. This is a great improvement over the stock 15kHz > filter for contesting and situations where there are lots of > very strong close-in signals. > > You don't need any additional crystal filters in the K3 > beyond the stock 2.7kHz filter to listen to CW at a 600Hz or > 350Hz or 200Hz or whatever bandwidth. Just dial in the width > you want with the WIDTH, SHIFT, LO CUT and/or HI CUT > controls. You only need to consider additional crystal > filters if you operate in conditions where strong signals > close to your operating frequency (inside the 2.7kHz filter) > may deteriorate the excellent filtering of the DSP with IMD > and other interference. > > Because my primary Ham radio activity is contesting, having > crystal filters right at the bandwidths I use for each mode > is useful. It is one of many reasons why the K3 is my > favorite contest radio. But all these filters are not needed > by many K3 users. > > - For SSB, my default bandwidth is 1.5kHz and that is saved > as ALT-1 and as my standard SSB bandwidth on all my band-mode > memories. Specifically, the DSP filter is set at > 300-1800kHz. I'm currently using the 1.8kHz crystal filter > which is actually about 1.9kHz at the -6dB points. > > - For CW, my default bandwidth is 400Hz although I'd be just > as happy at 500Hz. It's just that I'm currently using the > 400Hz crystal filters. I seldom go below that, but > occasionally on 160 with heavy QRM I might go down to 250 or 200Hz. > > - For RTTY, my default bandwidth is 200Hz plus the Dual-Tone > Filter of additional cascaded 50Hz filters around each tone. > In theory, the bandwidth for 170Hz-shift RTTY should be > 250-300Hz, but I've found operationally that 200Hz works > great in my RTTY contesting. > > Note that the actual -6dB bandwidths of the "400Hz" and > "250Hz" filters are 435Hz and 370Hz respectively. You > definitely don't need both of those filters, although that's > exactly what I personally have right now because I failed to > consider the actual bandwidths when making my initial > selection. Don't make that mistake. > > Finally, you can set the point at which each crystal filter > kicks in as the DSP bandwidth is varied. I set my trigger > points per the -6db bandwidths of the various filters, not > the product name. Thus, the "250Hz" filter switches in at > 350Hz because its actual bandwidth is 370Hz. Since I receive > RTTY at 200Hz DSP bandwidth, a better crystal filter for me > in that mode might be the "200Hz" (225Hz actual) for maximum > strong signal protection. > > 73, > Ed - W0YK > > > 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? > > _______________________________________________ > 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 _______________________________________________ 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
