K3: 2.1 vs 1.8
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HI all,
I've previously written to Mike directly, but I now see so many comments here that seem "wrong" or potentially misleading to me (but not all), that I am compelled to comment to the reflector. Mike said, "I just dont want to hear a 59+10 signal that is 3 kc..from the frequency I am listening on" This type of SSB interference is better controlled by the DSP final bandwidth than by the selection of a narrower roofing filter. What readers should keep in mind is that the roofing filter and DSP are linked together. In other words, when you narrow the DSP to (and past) a certain point, the narrower roofing filter ALSO kicks in. This results in a poorly "controlled" experiment, ie, too many variables. Roofing filters work to help knock out IMD (intermod) which may be encountered when multiple, very strong signals (stronger than Mike's 59+10) populate the band. If you are hearing the station "next door" (in terms of frequency) on SSB interfering with your intended QSO, then you are NOT talking about something that a roofing is intended to prevent...that is the job of the final bandwidth (in the case of the K3, the DSP filtering). While it has been brought to light that there is a cascading effect of the multi-level filters, I find it hard to believe that you will run into more than a couple of situations per year (if that many) where you will appreciate the impact of using the 1.8kc roofing filter instead of the 2.1kc roofing filter for SSB. You will likely run into many situations per year where the DSP will work exactly as you wish. Again, I point to Mike's request, "I just dont want to hear a 59+10 signal that is 3 kc..from the frequency I am listening on." To me, this just screams DSP filter and NOT a narrower roofing filter. de Doug KR2Q _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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One aspect that Doug leaves out, however is that of audio quality.
Signals will sound different with different filtering. Using a 2.8 XFIL and DSP to make it 1.8 KHz, I found SSB signals to be a bit "tinny" and hard sounding. I installed a 1.8 KHz XFIL, and found the audio quality to be improved. It was quite noticeable as I turned the width control downwards to where the 1.8 XFIL kicked in - the audio experience sounded like a continuation of what I was hearing at 1.9, only (obviously) an itty bitty bit narrower. The tinniness and harshness was not present. All IMHO. 73, Steve NN4X On Sat, Jul 12, 2008 at 11:45 AM, Ron D'Eau Claire <[hidden email]> wrote: > Doug, KR2Q, presented a superb explanation of why one needn't sweat too much > over the "roofing" (first I.F.) filter in the K3. > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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> Using a 2.8 XFIL and DSP to make it 1.8 KHz, I found SSB
> signals to be a bit "tinny" and hard sounding. What were the LO CUT and HI CUT values that produced this "tinny and hard sounding" audio? In both my K3s, the audio sounds great and it sounds identical, whether I use the 2.8 or the 1.8 kHz crystal filter with the DSP LO CUT = 200 Hz and HI CUT = 2 kHz. No way it could be called "tinny" or hard sounding. 73, Ed - W0YK _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by DOUGLAS ZWIEBEL
On Sat, 12 Jul 2008 06:13:31 -0400, DOUGLAS ZWIEBEL wrote:
>Roofing filters work to help knock out IMD (intermod) which may be >encountered when multiple, very strong signals (stronger than Mike's >59+10) populate the band. YES! It's important to remember that the add-in filters are ROOFING filters, not IF filters. The K3 does its own IF filters in DSP, and they work very well. The add-in filters mostly matter in the really intense conditions of contesting and DX chasing, especially when W0YK, K6XX, N6RZ, and W6DRX are all very close neighbors. Luckily, three of thm An hour or so of SSB time during IARU made me pretty comfortable with my choice of the 8-pole 1.8 kHz filter, and also the setting of 2.2 kHz for when it kicks in. I do agree with W0YK and others about the IF shift. Still some tweaking and listening to be done with shift and bandwidth of the IF filters, but I do like the sound of how they cascade, and I do agree with those who feel that the 1.8 kHz 8-pole filter is the one to buy for SSB contesting. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by AC7AC
"Engineering is *always* about compromises. -- Ron AC7AC"
While I certainly agree in theory, I don't think I'm making many with the K3. I picked my roofing filters on the basis of contesting and non-contesting. For non-contesting there's very little that strains the DSP. For general puttering about with 800-1000 hz CW, the 1.8 roofing is good enough. DSP does it. For puttering SSB, the 5 pole 2.7 does it. For SSB contesting, started with stock in the MP, then 2.1 INRAD's, and finally 1.8 INRAD's. So it's 1.8 in the K3, been there, done that. I never use the 1.8 in puttering mode, I use 1.8 exclusively in contests. For CW contesting, I go on the basis that there is an S9+40 station up 500 hz. I set my roofing filter to the width I want to hear and the DSP to match (400 for running and 250 for S&P). With a 5 element 40m quad on Europe out at NY4A, and certain Europeans running "plentiful" power plus yagis, S9+40 up 500 hz is common past experience, not conjecture. BC carriers are often off scale. In the K3 the 400 clearly whacks down the S9+40 up 500 down to a DSP manageable value. To wit: At home (not NY4A) I was listening to a 40 over BC signal on 7125 last night with the K3 on 8 pole 400. Even turning on the preamp (carrier 60 over tuned in), tuned up and down 500 hz I could hear right down to S3 ish noise on speech breaks with fast AGC on. I could also hear their buzzy 120 hz harmonic residuals (100 db below carrier?) between QRN peaks. All that with no ringing. MP can't get anywhere near that using 2nd and 3rd IF INRAD 400's. Thas what I need. I didn't notice any compromises running around anywhere. Also, FWIW, when I added DSP to my K2's A->B mods it really improved performance. K2 sounds a bunch more like the K3 than the MP, either way you read that sentence. 73, Guy K2, K3 #1239 |
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