Hearing the effect of narrower roofing filter
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All,
My K3 (with one extra roofing filter for CW) is not here yet, so I am asking this question without direct experience. It will be interesting to do an A/B comparison to see how the receiver sounds with/without the narrow crystal filter for a given bandwidth. I suspect this kind of test is of interest to many K3 owners. However, to be meaningful, it must be carried out properly. I want to ask the group: 1. How best to carry out such a test, and 2. What say those that have already tested. As to how to carry out the test, I think I read somewhere that the narrow filter can be disabled from the radio front panel. (Someone please correct me if I am wrong.) Now doing so, without changing the DSP bandwidth, is going to change the overall bandwidth unless the narrow crystal filter being disabled is already considerably wider than the DSP bandwidth. The case where the crystal filter is narrower than the DSP width setting is obviously going to result in less noise when the crystal filter is in, so that is not the case I am interested in. If the crystal filter is nominally the same width as the DSP filter, that is an interesting case. The composite width would then be narrower than the DSP alone (actually with say an SSB crystal filter). To make the comparison properly, when one takes out the narrow crystal filter (replaces it with an SSB crystal filter), one would probably need to change the DSP filter width to a narrower setting in order to get the same overall filter width. This wouldn't work out unless the required change in DSP width happens to match one of the available DSP width settings. If the crystal filter is moderately wider than the DSP setting, say using (vs not using) a 1 kHz crystal filter with a DSP setting of 500 Hz, that is an interesting situation that should be common in the K3. In this case maybe one can leave the DSP at 500 Hz, and just listen for any change. What kind of change am I talking about? If there is a signal within the crystal filter bandwidth that is strong enough to pump the hardware AGC, then I would expect to hear increased qsb to the down side. The point of the experiment would then be to assess how bothersome this effect is in a real situation. Is the narrow crystal filter worth it? While doing this, I would really like to see an indicator that shows the hardware AGC kicking in. Is there any way to see this on the K3, short of hanging a scope on the AGC line? On another line of thinking, reality tends to be complex, and, especially after the hardware AGC trigger level was raised (I think that is what was done??), maybe the composite of random noise and multiple strong signals in the crystal filter passband can produce some very short-lived signal peaks that either overload the ADC or by non-linear effects can generate additional audible noise in the case where the narrow crystal filter is not used? Whatever the cause, I am very interested in any noise increase that is actually audible in a real-life case with the K3, as a result of not having the ideal crystal filter for a given effective receiver bandwidth, especially for the case where NO ONE strong signal within any of the available crystal filters is strong enough to activate the hardware AGC. What has been observed by the group? 73, Erik K7TV _______________________________________________ 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 |
RE: Hearing the effect of narrower roofing filter
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-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Erik N Basilier My K3 ... interesting to do an A/B comparison to see how the receiver sounds with/without the narrow crystal filter for a given bandwidth. ... What has been observed by the group? --------------------------- I've not attempted such a complex test as you described (which I snipped out). I have the 500 Hz filter in my rig. As I narrow the DSP from 2 KHz to 550 Hz, I can hear a predictable narrowing of the passband with each step. When I step to 500 Hz and the narrow roofing filter kicks in, I can hear a distinct change, more than just the DSP narrowing I'd heard while stepping from 1000 Hz to 550 Hz. The effect is very noticeable. I don't think you'd have to construct some sort of (artificial) double-blind test to see what it does. Besides, what you really want to know is how does it play on the air. The best way to learn that is to play on the air :-) I have been able to get AGC pumping if I try. In all cases, going from 550 Hz to 500 Hz bandwidth took care of the pumping (roofing filter works) - Keith N1AS - - K3 711 - _______________________________________________ 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 |
Re: Hearing the effect of narrower roofing filter
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Darwin, Keith wrote:
> each step. When I step to 500 Hz and the narrow roofing filter kicks > in, I can hear a distinct change, more than just the DSP narrowing I'd > heard while stepping from 1000 Hz to 550 Hz. The effect is very > noticeable. > > - Keith N1AS - > - K3 711 - Keith, Can you describe this "change" closer. 73 Jim SM2EKM _______________________________________________ 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 |
RE: Hearing the effect of narrower roofing filter
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Keith Darwin wrote:
>> each step. When I step to 500 Hz and the narrow roofing filter kicks >> in, I can hear a distinct change, more than just the DSP narrowing I'd >> heard while stepping from 1000 Hz to 550 Hz. The effect is very >> noticeable. Jim replied: > Keith, Can you describe this "change" closer. We'll, let's see. When the 500 Hz filter kicks in, the resulting audio becomes more focused. There are noticeably less highs and esp. lows. Any low rumbly "grunge" from off freq. signals drops to zero and high freq chatter becomes much weaker. I like the effect and find the rig to be more pleasing to use at 500 Hz than at 550 Hz due to the steeper compound filter skirts. I'm considering a 1000 Hz roofing filter to make the rig sound better between 550 and 1000 Hz bandwidth. - Keith N1AS - - K3 711 - _______________________________________________ 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 |
RE: Hearing the effect of narrower roofing filter
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In reply to this post by Darwin, Keith
That's just what I find, too. Particulaly when operating PSK, when I reduce the filter with towards 500Hz I hear the tones of out of band stations gradually being reduced by each step. When the 500Hz filter kicks in the tones suddenly disappear altogether.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
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In reply to this post by Jan Erik Holm
----- Original Message -----
From: "Jan Erik Holm" <[hidden email]> Cc: <[hidden email]> Sent: Tuesday, July 08, 2008 8:31 AM Subject: Re: [Elecraft] Hearing the effect of narrower roofing filter > Darwin, Keith wrote: >> each step. When I step to 500 Hz and the narrow roofing filter kicks >> in, I can hear a distinct change, more than just the DSP narrowing I'd >> heard while stepping from 1000 Hz to 550 Hz. The effect is very >> noticeable. >> >> - Keith N1AS - >> - K3 711 - > Keith, > > Can you describe this "change" closer. > > 73 Jim SM2EKM Get two pieces of plastic pipe about a foot long. One six inches in diameter. One three inche in diameter. Close one eye and look at the mountains in the horizon and you will see a wide view. 6000 Hz Put the six inch pipe up to the other eye. You will see a portion of the horizon - like 1000 Hz. Put the three inch pipe up to your eye. 500 Hz. The effect, as Keith says, is very noticeable! 73 Hank K8DD ____________________________________________________________ GET FREE SMILEYS FOR YOUR IM & EMAIL - Learn more at http://www.inbox.com/smileys Works with AIM®, MSN® Messenger, Yahoo!® Messenger, ICQ®, Google TalkT and most webmails _______________________________________________ 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 |
Re: Re: Hearing the effect of narrower roofing filter
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In reply to this post by K7TV
Fine observations when you change the filter setting knob, but what makes you think you are hearing the effect of the roofing filter and not the dsp filter?
David G3UNA > > From: "hank k8dd" <[hidden email]> > Date: 2008/07/08 Tue PM 02:29:08 BST > To: "Jan Erik Holm" <[hidden email]> > CC: [hidden email] > Subject: Re: [Elecraft] Hearing the effect of narrower roofing filter > > ----- Original Message ----- > From: "Jan Erik Holm" <[hidden email]> > Cc: <[hidden email]> > Sent: Tuesday, July 08, 2008 8:31 AM > Subject: Re: [Elecraft] Hearing the effect of narrower roofing filter > > > > Darwin, Keith wrote: > >> each step. When I step to 500 Hz and the narrow roofing filter kicks > >> in, I can hear a distinct change, more than just the DSP narrowing I'd > >> heard while stepping from 1000 Hz to 550 Hz. The effect is very > >> noticeable. > >> > >> - Keith N1AS - > >> - K3 711 - > > Keith, > > > > Can you describe this "change" closer. > > > > 73 Jim SM2EKM > > Get two pieces of plastic pipe about a foot long. > One six inches in diameter. > One three inche in diameter. > Close one eye and look at the mountains in the horizon and you will see a > wide view. 6000 Hz > Put the six inch pipe up to the other eye. You will see a portion of the > horizon - like 1000 Hz. > Put the three inch pipe up to your eye. 500 Hz. > The effect, as Keith says, is very noticeable! > > 73 Hank K8DD > > ____________________________________________________________ > GET FREE SMILEYS FOR YOUR IM & EMAIL - Learn more at http://www.inbox.com/smileys > Works with AIM®, MSN® Messenger, Yahoo!® Messenger, ICQ®, Google TalkT and most webmails > _______________________________________________ > 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 > ----------------------------------------- Email sent from www.virginmedia.com/email Virus-checked using McAfee(R) Software and scanned for spam _______________________________________________ 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 |
RE: Re: Hearing the effect of narrower roofing filter
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Not sure, David, if your Q was to me or to Hank. I can only answer for
me. When I adjust the filter width knob, I'm most definitely hearing the combined effect of the DSP bandwidth reduction and the change in roofing filters. But, since I can change DSP without changing the roofing filter (by stepping from 1500 Hz down to 550 Hz) I can get a good feel for how the DSP filter sounds. Then, stepping to 500 Hz, I can see the combined effect of one more DSP step plus the insertion of the 500 Hz roofing filter. The observed big change from 550 Hz to 500 Hz is *mostly* due to the roofing filter. - Keith N1AS - - K3 711 - ----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of [hidden email] Fine observations when you change the filter setting knob, but what makes you think you are hearing the effect of the roofing filter and not the dsp filter? David G3UNA _______________________________________________ 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 |
RE: Re: Hearing the effect of narrower roofing filter
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A couple of related points, which may not be new news to anyone:
You can set the K3's filter bandwidth configuration to cause the roofing filter to switch at points other than the bandwidth printed on the filter. Maybe you would like your (nominally) 500 Hz filter to switch in at 450 or 550 Hz. My 8-pole 250 Hz filter is a bit broader than 250 Hz, and I've set it to switch at 300 Hz. You can also turn off a filter (set its bandwidth to zero temporarily) to evaluate whether a change you're hearing is due to the roofing filter or the change in bandwidth provided by the DSP. And you should attempt to adjust the filter gain compensation so that there is no change in the volume of the note you're tuned to. Rene, who guides the assembly of K3s built by Elecraft, told me that he uses a voltmeter on the speaker terminals when adjusting the gain compensation and can get usually get within a half decibel. I notice a definite qualitative change as the narrower filters switch in. It sounds quieter, and it seems like the volume is being turned down. I think I'm responding to the reduced low and high frequency components that are supposed to be cut off. The DSP-related changes seem more gradual. Dick, K6KR -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Darwin, Keith Sent: Tuesday, July 08, 2008 7:43 AM To: [hidden email] Subject: RE: Re: [Elecraft] Hearing the effect of narrower roofing filter Not sure, David, if your Q was to me or to Hank. I can only answer for me. When I adjust the filter width knob, I'm most definitely hearing the combined effect of the DSP bandwidth reduction and the change in roofing filters. But, since I can change DSP without changing the roofing filter (by stepping from 1500 Hz down to 550 Hz) I can get a good feel for how the DSP filter sounds. Then, stepping to 500 Hz, I can see the combined effect of one more DSP step plus the insertion of the 500 Hz roofing filter. The observed big change from 550 Hz to 500 Hz is *mostly* due to the roofing filter. - Keith N1AS - - K3 711 - ----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of [hidden email] Fine observations when you change the filter setting knob, but what makes you think you are hearing the effect of the roofing filter and not the dsp filter? David G3UNA _______________________________________________ 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 No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 6:33 AM No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 6:33 AM _______________________________________________ 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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K6KR wrote:
>I notice a definite qualitative change as the narrower filters switch in. It sounds quieter, and it seems like the volume is being turned down. I think I'm responding to the reduced low and high frequency components that are supposed to be cut off. The DSP-related changes seem more gradual. Dick made some very good points about using the K3Utility to enable different filters and about the need to set gain correctly for each filter. Here's a simple test that may surprise you: 1. Disable all filters but your 2.7 or 2.8 for CW (using Dick's K3Utility). 2. SLOWLY rotate WIDTH from 1.5 to 0.05. 3. Note how the character of the noise changes. I find abrupt changes in noise character between some DSP settings...and this is *not* due to the roofing filter since that is held constant at 2.7k. The abrupt changes I hear using a 350 Hz CW pitch setting are: 1.1 - 1.0 0.90-0.85 0.70-0.65 0.50-0.45 0.30-0.25 0.20-0.15 Do you see a pattern in the above? I hear something which repeats almost every 0.20 increment...(and I bet Lyle can explain why). I recall seeing this on Spectrogram when I was closely looking at DSP BWs shortly after I got my unit. We did discover some serious offset problems at the low end (which Lyle has since fixed), but I recall the DSP BW changes were never exactly linear as you reduced BW. This is not a particular concern to me but curious nevertheless. 73, Bill |
RE: Re: Hearing the effect of narrower roofing filter
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In reply to this post by Dick Dievendorff
I agree with this assessment and when I get my rig back plan on upping
my 250 filter to kick in at 350. But I had 4dB of gain on the 250 and it still seemed like things got a lot quieter when switching to the 250. I'd have to measure and see if I had the actual same level there (and I can do that now that I have the XG2) :).... But I did have 4dB thrown in for good measure! :) I found myself using the 250 all the time for rag chewing... But I use 250 on my K1 for its lowest filter position too.. I tend to generally like things pretty quiet. I use 850 for scanning the band (as that is as wide as the K1 can go). I use 500 to 550 for calling CQ if they're further away than that then I guess I don't get to hear them... And then I crank it down to 200 to 250 when I'm talking with a guy. It not only ensures that I'm pretty close to zero beat with him but also makes things quieter and gets rid of a lot of the electrical hash I have in my area. The K1's noise blanker doesn't hold a candle to the noise in my area but the K3 was doing a pretty fantastic job! On Tue, 2008-07-08 at 08:02 -0700, Dick Dievendorff wrote: > A couple of related points, which may not be new news to anyone: > > You can set the K3's filter bandwidth configuration to cause the roofing > filter to switch at points other than the bandwidth printed on the filter. > Maybe you would like your (nominally) 500 Hz filter to switch in at 450 or > 550 Hz. My 8-pole 250 Hz filter is a bit broader than 250 Hz, and I've set > it to switch at 300 Hz. > > You can also turn off a filter (set its bandwidth to zero temporarily) to > evaluate whether a change you're hearing is due to the roofing filter or the > change in bandwidth provided by the DSP. > > And you should attempt to adjust the filter gain compensation so that there > is no change in the volume of the note you're tuned to. Rene, who guides > the assembly of K3s built by Elecraft, told me that he uses a voltmeter on > the speaker terminals when adjusting the gain compensation and can get > usually get within a half decibel. > > I notice a definite qualitative change as the narrower filters switch in. It > sounds quieter, and it seems like the volume is being turned down. I think > I'm responding to the reduced low and high frequency components that are > supposed to be cut off. The DSP-related changes seem more gradual. > > Dick, K6KR > > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Darwin, Keith > Sent: Tuesday, July 08, 2008 7:43 AM > To: [hidden email] > Subject: RE: Re: [Elecraft] Hearing the effect of narrower roofing filter > > Not sure, David, if your Q was to me or to Hank. I can only answer for > me. > > When I adjust the filter width knob, I'm most definitely hearing the > combined effect of the DSP bandwidth reduction and the change in roofing > filters. But, since I can change DSP without changing the roofing > filter (by stepping from 1500 Hz down to 550 Hz) I can get a good feel > for how the DSP filter sounds. Then, stepping to 500 Hz, I can see the > combined effect of one more DSP step plus the insertion of the 500 Hz > roofing filter. The observed big change from 550 Hz to 500 Hz is > *mostly* due to the roofing filter. > > - Keith N1AS - > - K3 711 - > > ----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of > [hidden email] > > Fine observations when you change the filter setting knob, but what > makes you think you are hearing the effect of the roofing filter and not > the dsp filter? > > David > G3UNA > > _______________________________________________ > 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 > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 > 6:33 AM > > > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 > 6:33 AM > > _______________________________________________ > 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 _______________________________________________ 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 |
Re: Re: Hearing the effect of narrower roofing filter
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In reply to this post by Darwin, Keith
The reason I'm particularly interested is because I fancy doing diversity
reception and de-select my roofing filters in the main rx so there is no phase shifting relative to the second rx without filters. Have you de-selected the roofing filters to do a comparison with and without? David G3UNA When I adjust the filter width knob, I'm most definitely hearing the combined effect of the DSP bandwidth reduction and the change in roofing filters. But, since I can change DSP without changing the roofing filter (by stepping from 1500 Hz down to 550 Hz) I can get a good feel for how the DSP filter sounds. Then, stepping to 500 Hz, I can see the combined effect of one more DSP step plus the insertion of the 500 Hz roofing filter. The observed big change from 550 Hz to 500 Hz is *mostly* due to the roofing filter. - Keith N1AS - - K3 711 - _______________________________________________ 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 |
Re: Re: Hearing the effect of narrower roofing filter
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In reply to this post by Dick Dievendorff
But if you leave the setting at its nominal, can you hear the difference as
that bandwidth is selected? I'm not sure I understand the advantage you are gaining by bringing the crystal filter in later; I'll do if there's something to be gained, it sounds an interesting approach. David G3UNA >A couple of related points, which may not be new news to anyone: > > You can set the K3's filter bandwidth configuration to cause the roofing > filter to switch at points other than the bandwidth printed on the filter. > Maybe you would like your (nominally) 500 Hz filter to switch in at 450 or > 550 Hz. My 8-pole 250 Hz filter is a bit broader than 250 Hz, and I've > set > it to switch at 300 Hz. > > You can also turn off a filter (set its bandwidth to zero temporarily) to > evaluate whether a change you're hearing is due to the roofing filter or > the > change in bandwidth provided by the DSP. > > And you should attempt to adjust the filter gain compensation so that > there > is no change in the volume of the note you're tuned to. Rene, who guides > the assembly of K3s built by Elecraft, told me that he uses a voltmeter on > the speaker terminals when adjusting the gain compensation and can get > usually get within a half decibel. > > I notice a definite qualitative change as the narrower filters switch in. > It > sounds quieter, and it seems like the volume is being turned down. I think > I'm responding to the reduced low and high frequency components that are > supposed to be cut off. The DSP-related changes seem more gradual. > > Dick, K6KR > > 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 |
RE: Re: Hearing the effect of narrower roofing filter
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In reply to this post by David Cutter
Nope, I have not. My operating (near zero right now due to "life" getting in the way) is 99.9% CW, old school, with manual keys. I'm not pushing the envelop so I'm not trying new & novel things. These days, I pretty much just use my rig rather than playing & testing with it. - Keith N1AS - - K3 711 - -----Original Message----- Have you de-selected the roofing filters to do a comparison with and without? _______________________________________________ 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 |
RE: Re: Hearing the effect of narrower roofing filter
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In reply to this post by David Cutter
I'm not completely sure what to do with this capability, other than perhaps
have the switchover occur at a bandwidth that more closely matches the filter you actually have. What I've done is tell the K3 that my 250 Hz filter is really 300 Hz (it's really probably more like 370 Hz). I also have a 400 Hz filter. I didn't make a particularly wise choice of filter bandwidths. To those who have pointed out the error of my ways, my defense is that I chose the filters on first order day before the curves were published on the web site. I don't view this as a severe issue. Maybe I should have ordered the 200 Hz 5-pole instead, but I got it into my head that maybe the 8-pole filters were "better" in some way. I didn't repeat this mistake when I ordered filters for the subreceiver. Dick, K6KR -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of David Cutter Sent: Tuesday, July 08, 2008 10:18 AM To: [hidden email] Subject: Re: Re: [Elecraft] Hearing the effect of narrower roofing filter But if you leave the setting at its nominal, can you hear the difference as that bandwidth is selected? I'm not sure I understand the advantage you are gaining by bringing the crystal filter in later; I'll do if there's something to be gained, it sounds an interesting approach. David G3UNA >A couple of related points, which may not be new news to anyone: > > You can set the K3's filter bandwidth configuration to cause the roofing > filter to switch at points other than the bandwidth printed on the filter. > Maybe you would like your (nominally) 500 Hz filter to switch in at 450 or > 550 Hz. My 8-pole 250 Hz filter is a bit broader than 250 Hz, and I've > set > it to switch at 300 Hz. > > You can also turn off a filter (set its bandwidth to zero temporarily) to > evaluate whether a change you're hearing is due to the roofing filter or > the > change in bandwidth provided by the DSP. > > And you should attempt to adjust the filter gain compensation so that > there > is no change in the volume of the note you're tuned to. Rene, who guides > the assembly of K3s built by Elecraft, told me that he uses a voltmeter on > the speaker terminals when adjusting the gain compensation and can get > usually get within a half decibel. > > I notice a definite qualitative change as the narrower filters switch in. > It > sounds quieter, and it seems like the volume is being turned down. I think > I'm responding to the reduced low and high frequency components that are > supposed to be cut off. The DSP-related changes seem more gradual. > > Dick, K6KR > > 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 No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 6:33 AM No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.4.6/1540 - Release Date: 7/8/2008 6:33 AM _______________________________________________ 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 David Cutter
<quote author="David Cutter">
But if you leave the setting at its nominal, can you hear the difference as that bandwidth is selected? I'm not sure I understand the advantage you are gaining by bringing the crystal filter in later; I'll do if there's something to be gained, it sounds an interesting approach. David G3UNA David, Say that you have a 500 Hz (nominal) roofing filter with an (actual) 6-dB bandwidth of 550 Hz. When you choose the widest DSP bandwidth at which this roofing filter kicks in, here is what I think about the choices you have: 1. You have it kick in at 550 Hz DSP because it matches the DSP bandwidth. This may create the steepest slopes, but I would avoid it for digital modes since I would expect the group delays to vary near the flanks of the xtal filter, but not near the flanks of the (FIR) DSP filter. 2. You have it kick in at 500 Hz DSP because it is a "500 Hz filter". This logic makes no sense, since the xtal filter is actually 550 Hz. 3. You have it kick in at 500 Hz or less DSP because you want the DSP to cut away the group-delay-varying portion of the xtal filter passband. This would make sense. How much of the xtal filter response would of course depend on the group delay characteristics of the particular xtal filter. Of course if you don't use digital modes, you may want to go with approach #1. 4. You have it kick in at 600 Hz or above. Someone on the list suggested that this approach made the receiver sound more pleasant. The effect would essentially be to disable the DSP for receive purposes, except for the DSP's big improvement in ultimate rejection, and any bandwidth-unrelated DSP function that may be enabled. I have yet to hear for myself, but operating this way makes little sense to me unless there is something wrong with the DSP release. As to my original question, it seems that most respondents like to vary the DSP bandwidth as a means of switching the narrow xtal filter in and out, and to do this without lots of strong closeby signals. If the xtal filter kicks in according to #1 above, the composite bandwith of the two 550-Hz filters will be much less than 550 Hz. This will of course create an exaggerated effect of reducing the noise you hear, and here is an obvious risk of giving the narrow xtal filter way too much credit. If instead the kick-in point is set according to #3, you would reduce the effect of cascading on the overall bandwidth, and results would be more meaningful. However, as has been pointed out, it would be necessary to carefully adjust the gain for the xtal filter. Also, you would have to somehow work around the variations in effective DSP bandwidth step size, which have been stated to differ from the expected 50 Hz steps (at every 200 Hz?). Anyway, what I really wanted to know was NOT how the filters sound with just background hiss or average signals on the band. The justification for the narrow roofing filter would exist only if very strong interfering signal levels get through the standard roofing filter. I am thinking CW, and in case there is only one such signal, the AGC pumping would be easy to recognize. My understanding is that with current production K3's this would happen for an interfering signal level of somewhere around 25 to 30 dB over S9. In my mind, the interesting question is the case where there are multiple interfering signals within the roofing filter passband, including qrn etc. Even though these would not add up coherently, the peak voltage would grow with the number of signals, such that the ADC overload level would be reached without any individual signal reaching the 25 or 30 dB over S9. This suggests that the hardware AGC ideally should have an extremely fast attack time, and I assume that it does. When the hardware AGC responds under these conditions, I am guessing that the effect might be an increase in the general background noise heard. This is really what I was after. |
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In reply to this post by Dick Dievendorff
<quote author="Dick Dievendorff"> ..... Maybe I should have ordered the 200 Hz 5-pole instead, but I got it into my head that maybe the 8-pole filters were "better" in some way. I didn't repeat this mistake when I ordered filters for the subreceiver. Dick, K6KR I know I will incur some religious wrath from some.... however here is the OTHER side of that argument. It's not that I am denying the issues that are raised to question getting the two 8 pole CW filters (400 and 300 in actuality). I am solving a SINGLE happenstance which occurs over, over, over and over again in contests, so much so that until the K3 it was in my mind the LIMITING issue in improving 40m CW DX scores. I am at a contest station in eastern NC just off Pamlico Sound. On 40m to Europe we are using a 5 element wire quad suspended across a 220 foot NE/SW catenary between two towers. Broadcast signals above 7.1 routinely peg meters and light all the lights. So do some US stations in the NE, and so do some number of VERY LOUD European stations (VLS). WHAT they are doing to be so loud is not part of my exposition. They just are very loud. At some point in the contest, one has worked all the VLS, loud, medium and well-antenna'd QRP signals. What remains is a bewildering and seemingly bottomless pool of stations that can hear us (QRO on 5 elements) and are trying to work us on antennas with the gain of a basement floor joist wet noodle antenna. There are hundreds and hundreds of these. We have some number of recordings made in Europe of these, and they are quite weak over there. It is guaranteed, only a matter of time, and sometimes immediate, that a VLS will settle in the next slot above or below. They may be as close as 350 Hz. The problem now is working the QRP wet noodle station who is into the noise without hardware AGC pumping or other effects from a VLS INSIDE the roofing filter that was set to hear stations who will call sometimes +/- 200-250 Hz. I need the roofing filter is to get down 30 db as quickly as possible, without giving up too much of the +/- 250 Hz. The 400 Hz is a good width even for VLS +/- 500 Hz. If a VLS squeezes me on one side, I only want to give up +/- real estate in the roofing filter on that side. The procedure is to drop to 300 hz roofing and DSP and move the RX center 50 hz away from TX frequency and the VLS. I give up listening so far on the side of the VLS, but keep the real estate on the other side. It is a matter of the width out to the edge and the largest db drop per 10 hz in the skirts thereafter. The roofing filter keeps the VLS from getting into the hardware AGC or pushing the DSP to the extreme. I have used both of these filters for years in my FT1000MP and am completely familiar with their shape and use in a contest. I have heard it said that the 200 5 pole filter will do better for picking out signals in a very crowded situation, perhaps so in an extremely tight situation. But thus far I have been able to go narrow with the 300 8 pole and it is the DSP handling the work there. At some point I would like to be able to tune the center of the DSP CW selectivity up/down at 25 Hz rate using RIT *WITHOUT* moving the position of the roofing filter relative to the band. The point of the roofing filter is to reject the VLS in the next slot above and below me. Tune the whole thing up or down to listen to a weak station off-frequency for whatever reason and you let one of the VLS in under the roof. Just the view from the other side of the river... :>) 73, Guy. |
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Guy,
Wouldn't a deep, tunable narrow notch filter also be a solution. The present notch filter is as wide as a barn door and useless for CW. I'm not a DSP programmer, but wonder how hard it could be to implement one. After there is a narrow "notch" in the present RTTY dual passband filter. If one can do a double hump filter with notch in the middle, why not just a narrow notch filter? 73 de Brian/K3KO <quote author="Guy, K2AV">
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RE: Hearing the effect of narrower roofing filter
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In reply to this post by Guy, K2AV
Guy, > I need the roofing filter is to get down 30 db as quickly as > possible, without giving up too much of the +/- 250 Hz. A careful comparison of the 500 Hz 5-pole filter, 400 Hz 8-pole filter, "250 Hz" 8 pole filter and 200 Hz 5 pole filter shows some interesting things ... 1) my "500 Hz" filter is really 470 Hz at - 6dB ... this is consistent (460 - 490 Hz) with measurements reported by others. I intend to check the two other 500 Hz filters received with my second K3/KRX3 when I have some time. 2) the -30 dB bandwidth of my 500 Hz filter (780 Hz) is not significantly different than the -30 dB bandwidth of the 400 Hz filter reported on the Elecraft web site (680 Hz) when cascaded with a DSP filter at 400 or 500 Hz. I set my K3 so the "500 Hz" filter engages at 450 Hz. It is on-line when normalizing the CW filters but is off-line when selecting a composite bandwidth wider than the filter. 3) the 200 Hz five pole filter (209 Hz measured) is narrower than the 250 Hz filter down to at least -40 dB without any any benefit from cascading with DSP. For CW specifically, it's hard to justify the 400/250 Hz pair with their relatively small difference in bandwidth and their significantly greater cost compared to the 500/200 Hz pair. To be an effective alternative to the 400 Hz (450 Hz from Inrad curves, 435 Hz from Elecraft curves) filter, the 250 Hz 8-pole really needs to be held to the nominal 250 Hz bandwidth so that the difference will be useful. Even in a "worst case" (e.g. 40 meters in Europe) scenario, reducing the pre-DSP bandwidth from 450 to 370 Hz is not likely to be significant. > I have used both of these filters for years in my FT1000MP > and am completely familiar with their shape and use in a > contest. The 250 Hz filters in an FT1000MP is an entirely different situation. In the FT-1000D/FT-1000MP, there are two filters - each approximately 350 Hz wide - in cascade yielding a composite 250 Hz (at -6dB) bandwidth. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Guy, K2AV > Sent: Sunday, August 31, 2008 10:46 AM > To: [hidden email] > Subject: Re: [Elecraft] Hearing the effect of narrower roofing filter > > > > > > ..... Maybe > I should have ordered the 200 Hz 5-pole instead, but I got it > into my head that maybe the 8-pole filters were "better" in > some way. I didn't repeat this mistake when I ordered > filters for the subreceiver. > > Dick, K6KR > > I know I will incur some religious wrath from some.... > however here is the OTHER side of that argument. It's not > that I am denying the issues that are raised to question > getting the two 8 pole CW filters (400 and 300 in actuality). > > I am solving a SINGLE happenstance which occurs over, over, > over and over again in contests, so much so that until the K3 > it was in my mind the LIMITING issue in improving 40m CW DX scores. > > I am at a contest station in eastern NC just off Pamlico > Sound. On 40m to Europe we are using a 5 element wire quad > suspended across a 220 foot NE/SW catenary between two towers. > > Broadcast signals above 7.1 routinely peg meters and light > all the lights. > So do some US stations in the NE, and so do some number of > VERY LOUD European stations (VLS). WHAT they are doing to be > so loud is not part of my exposition. They just are very loud. > > At some point in the contest, one has worked all the VLS, > loud, medium and well-antenna'd QRP signals. What remains is > a bewildering and seemingly bottomless pool of stations that > can hear us (QRO on 5 elements) and are trying to work us on > antennas with the gain of a basement floor joist wet noodle > antenna. There are hundreds and hundreds of these. We have > some number of recordings made in Europe of these, and they > are quite weak over there. > > It is guaranteed, only a matter of time, and sometimes > immediate, that a VLS will settle in the next slot above or > below. They may be as close as 350 Hz. The problem now is > working the QRP wet noodle station who is into the noise > without hardware AGC pumping or other effects from a VLS > INSIDE the roofing filter that was set to hear stations who > will call sometimes +/- 200-250 Hz. > > I need the roofing filter is to get down 30 db as quickly as > possible, without giving up too much of the +/- 250 Hz. The > 400 Hz is a good width even for VLS +/- 500 Hz. If a VLS > squeezes me on one side, I only want to give up +/- real > estate in the roofing filter on that side. The procedure is > to drop to 300 hz roofing and DSP and move the RX center 50 > hz away from TX frequency and the VLS. I give up listening so > far on the side of the VLS, but keep the real estate on the > other side. > > It is a matter of the width out to the edge and the largest > db drop per 10 hz in the skirts thereafter. The roofing > filter keeps the VLS from getting into the hardware AGC or > pushing the DSP to the extreme. > > I have used both of these filters for years in my FT1000MP > and am completely familiar with their shape and use in a contest. > > I have heard it said that the 200 5 pole filter will do > better for picking out signals in a very crowded situation, > perhaps so in an extremely tight situation. But thus far I > have been able to go narrow with the 300 8 pole and it is the > DSP handling the work there. > > At some point I would like to be able to tune the center of > the DSP CW selectivity up/down at 25 Hz rate using RIT > *WITHOUT* moving the position of the roofing filter relative > to the band. The point of the roofing filter is to reject > the VLS in the next slot above and below me. Tune the whole > thing up or down to listen to a weak station off-frequency > for whatever reason and you let one of the VLS in under the roof. > > Just the view from the other side of the river... :>) > > > 73, Guy. > > -- > View this message in context: > http://n2.nabble.com/Hearing-the-effect-of-narrower-roofing-fi Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ 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 _______________________________________________ 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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>> I have used both of these filters for years in my FT1000MP >> and am completely familiar with their shape and use in a >> contest. >The 250 Hz filters in an FT1000MP is an entirely different >situation. In the FT-1000D/FT-1000MP, there are two filters >- each approximately 350 Hz wide - in cascade yielding a >composite 250 Hz (at -6dB) bandwidth. In my MP, having INRAD pairs at 400 and 250, one often used tactic was leaving the 455 IF at 400 (500 on the panel) and switching in the "250" in the 2nd If, to deal with a VLS squeezing in from above or below. Though it was certainly useful, the other cr*p being generated by the IF in the MP prevented making best use of the filters. I don't expect anything else roofing wise from them in the K3. The "mere" 100 Hz difference in the two is enough to deal with a squeezing-in VLS I already had compared the K3 website curves with my measured MP curves on the two filters with the 455 IF set wide, so I knew exactly what I was getting. In the WAE, this setup performed spendidly as expected. I had dsp width set to get the wider CW filter at 500 Hz dsp, narrower CW filter at 300 dsp. That's why *I* bought the two, with my eyes wide open, I make no claims to have the fully portable mantra for everyone to follow, just a view from another perspective. 73, and even if your mileage may vary may it still take you where you want to be. Guy, K2AV |
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