Analysis of FT-1000 APF
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I assumed that the front panel control was a 1k potentiometer. Probably a reasonable guess. As the pot is tuned from max to min resistance, the audio peak moves from 340 Hz to about 1000 Hz (as I reported earlier). The gain at the peak is like this: 340 Hz : 7.5 dB , Q = 11 485 Hz : 8.1 dB 600 Hz : 8.6 dB 740 Hz : 9.1 dB 850 Hz : 9.6 dB 1000 Hz : 10.5 dB , Q = 35 So it has the typical characteristic of an active filter as it's center frequency is tuned higher (it gets 'peakier'). Maybe this is more info than you all care about, but there it is. Should the front panel control be larger than 1k, then all it means is that it will tune lower in frequency than I have shown here. 'APF' is just a marketing term for a narrow audio band pass filter, at least in the FT-1000. I don't have any place I can post a picture of these plots, so my word description will have to do. Al W6LX --- On Sun, 8/16/09, Al Lorona <[hidden email]> wrote: From: Al Lorona <[hidden email]> Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same To: [hidden email], "Paul Christensen" <[hidden email]> Date: Sunday, August 16, 2009, 4:44 PM Yes, I ran the analysis on the circuit as shown, without the tuning control. If anyone wants to pore through the schematics and tell me the value of the control as well as where to put it, I'll be happy to run the analysis at the two ends of the range of the control. What I had wanted to do with my information was remove any mystery surrounding the topology of the circuit in the FT-1000. Now that we know what it is, it may help someone to try and duplicate it with hardware, software, or whatever. Al W6LX --- On Sun, 8/16/09, Paul Christensen <[hidden email]> wrote: From: Paul Christensen <[hidden email]> Subject: Re: [Elecraft] APF vs 10 Hz DSP, why they don't sound the same To: [hidden email] Date: Sunday, August 16, 2009, 4:39 PM > "The circuit surrounding op amp 3016-2 in the FT-1000 schematic is nothing > more than an active bandpass filter, center frequency of about 1025 Hz, Q > = 35, with a gain of about 10.5 dB." The APF filter is active on the Main Rx, CW mode only. However, Fc is not confined to 1025 Hz; with the front panel "APF" control, it's adjustable roughly over the range of the CW BFO offset when the filter switch is engaged. Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Bless your heart for working through that Al! I previously posted the FT-1000 data to the K3 Field Test list a few weeks back hoping someone might "bite" and do a circuit simulation, but alas nobody took the hook! I guess the heavy hitters at Elecraft were too busy with the P3. If I'm interpreting Q correctly, it appears the filter is ~30 Hz BW at all pitch settings (which would definitely be near "ring" territory). I've previously suggested to Lyle that DUAL PB use 50 Hz for the focus instead of 150 Hz, but I believe there was some problem with that (which I've since forgotten). If there were a way to do 50 Hz with the same -20 dB pedestal BW (600 Hz minimum), I think this could be a nice alternative to traditional APF. Of course the present 50 Hz BW is actually something like 80 Hz, so it would be nice if that could be made closer to 50 Hz or maybe even 30. Thanks again for doing the simulation! Maybe Wayne or Lyle will have a pleasant surprise for us one of these days. 73, Bill W4ZV |
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I'd rather see a menu setting in menu probably even rather than config
that allows one to set the focus BW and then use the width knob to set the width of the wider skirts. I think that also being able to set the depth of the step between the two filters would also be really nice. ~Brett (KC7OTG) On Sun, 2009-08-16 at 20:26 -0500, Bill W4ZV wrote: > > > Al Lorona wrote: > > > > > > I assumed that the front panel control was a 1k potentiometer. Probably a > > reasonable guess. > > > > As the pot is tuned from max to min resistance, the audio peak moves from > > 340 Hz to about 1000 Hz (as I reported earlier). The gain at the peak is > > like this: > > > > 340 Hz : 7.5 dB , Q = 11 > > 485 Hz : 8.1 dB > > 600 Hz : 8.6 dB > > 740 Hz : 9.1 dB > > 850 Hz : 9.6 dB > > 1000 Hz : 10.5 dB , Q = 35 > > > > So it has the typical characteristic of an active filter as it's center > > frequency is tuned higher (it gets 'peakier'). Maybe this is more info > > than you all care about, but there it is. > > > > Should the front panel control be larger than 1k, then all it means is > > that it will tune lower in frequency than I have shown here. > > > > 'APF' is just a marketing term for a narrow audio band pass filter, at > > least in the FT-1000. > > > > I don't have any place I can post a picture of these plots, so my word > > description will have to do. > > > > Bless your heart for working through that Al! I previously posted the > FT-1000 data to the K3 Field Test list a few weeks back hoping someone might > "bite" and do a circuit simulation, but alas nobody took the hook! I guess > the heavy hitters at Elecraft were too busy with the P3. > > If I'm interpreting Q correctly, it appears the filter is ~30 Hz BW at all > pitch settings (which would definitely be near "ring" territory). I've > previously suggested to Lyle that DUAL PB use 50 Hz for the focus instead of > 150 Hz, but I believe there was some problem with that (which I've since > forgotten). If there were a way to do 50 Hz with the same -20 dB pedestal > BW (600 Hz minimum), I think this could be a nice alternative to traditional > APF. Of course the present 50 Hz BW is actually something like 80 Hz, so it > would be nice if that could be made closer to 50 Hz or maybe even 30. > > Thanks again for doing the simulation! Maybe Wayne or Lyle will have a > pleasant surprise for us one of these days. > > 73, Bill W4ZV > > -- > View this message in context: http://n2.nabble.com/Analysis-of-FT-1000-APF-tp3455867p3455987.html > Sent from the Elecraft mailing list archive at Nabble.com. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by alorona
Al, I found an online FT-1000 Service Manual and confirm that the APF pot (VR8901-2) is indeed 1k. Good guess! KC7OTG: > I'd rather see a menu setting in menu probably even rather than config that allows one to set the focus BW and then use the width knob to set the width of the wider skirts. I think that also being able to set the depth of the step between the two filters would also be really nice. Unfortunately that also makes it more complex which lessens the probabliity of it happening. If Elecraft *only* wanted to emulate the FT-1000 APF characteristic, they should narrow the 150 Hz focus of DUAL PB to whatever is practical (hopefully 30 Hz). The width of the -20 dB pedestal is already determined by the WIDTH setting in the present implementation (with the restriction that 600 Hz is the minimum). I tried the existing DUAL PB for awhile, found it contributed little to better CW copy and now it's one of several unused functions for me. I don't operate RTTY where the present dual peak filter is probably quite useful. 73, Bill |
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I don't see how its that much more complex. Look at the AGC. Its quite
complex and very adaptable. However if you don't wish it to be complex you can simply leave the settings at their defaults and move on with your life. I feel that the DUAL PB could operate in this same manner. Two menu parameters one for the step delta between the focus and skirts and then a parameter to allow one to set the focus width. Then its fully configurable. I think the adjustable step delta would be more important to my use of the DUAL PB more often with the adjustable focus width a close second. ~Brett (KC7OTG) On Sun, 2009-08-16 at 21:15 -0500, Bill W4ZV wrote: > Unfortunately that also makes it more complex which lessens the > probabliity > of it happening. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by alorona
Al if you could provide the 6 dB BW and 6/60 dB shape factors this would give Lyle an idea of what's needed in the DSP. If you send all 6 APF plots directly to me I'll post them for all to see (attachments must be sent directly since they will not go through the list filters). From what I recall of the DSP filter characteristics, they all have a constant ~150 Hz slope from -6 to -60 dB on the skirts. This means a nominal 150 Hz BW filter has a 3:1 shape factor and a *true* 50 Hz filter would have a 7:1 shape factor ([50+150+150]/50). So there are several issues for the DSP: 1. Can a true 50 Hz (or better yet 30 Hz) filter be constructed? 2. Is a shape factor of 7:1 sufficient for the peaking function to work as in the FT1000's APF? 3. Can the above be done on-the-fly without introducing latency or other problems? Thanks again for your work on this! 73, Bill |
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It turns out Al W6LX was one step ahead of me and had already sent me his PowerPoint file. It's viewable on the following link if you can read .ppt files (readers are available from Microsoft for free if you don't have PowerPoint installed): http://ft1000apf.googlepages.com/w6lxanalysisoftheapfcircuitintheft-1000 Just eyeballing the plots, I don't believe the current DSP filter implementation will duplicate the APF filter characteristic, but Lyle is the one to best determine that. 73, Bill |
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I've also posted it here as another mirror:
http://www.livecomputers.com/K3/FT_1000_APF.ppt On Mon, 2009-08-17 at 04:41 -0500, Bill W4ZV wrote: > > Bill W4ZV wrote: > > > > If you send all 6 APF plots directly to me I'll post them for all to see > > (attachments must be sent directly since they will not go through the list > > filters). > > > > It turns out Al W6LX was one step ahead of me and had already sent me his > PowerPoint file. It's viewable on the following link if you can read .ppt > files (readers are available from Microsoft for free if you don't have > PowerPoint installed): > > http://ft1000apf.googlepages.com/w6lxanalysisoftheapfcircuitintheft-1000 > > Just eyeballing the plots, I don't believe the current DSP filter > implementation will duplicate the APF filter characteristic, but Lyle is the > one to best determine that. > > 73, Bill > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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