Hearing CW - Fundamental Keying Waveform?
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Hearing CW - Fundamental Keying Waveform?
 
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The recent thread on filter settings and hearing reminded me of a question I
would like to get an answer to. In the ARRL 2001 Handbook on page 15.7 we find: "The dots and dashes of a CW signal must start and stop abruptly enough so we can clearly distinguish the carrier's presences and absences from noise, especially when fading prevails. The keying sidebands, which sound like little more than thumps when listened to on their own, help our brains be sure when the carrier tone starts and stops. It so happens that we always need to hear one or more harmonics of the fundamental keying waveform for the code to sound sufficiently crisp." What is meant by "the fundamental keying waveform"? How do we take "the need to hear one or more harmonics of the fundamental keying waveform" into account when setting up the IF and audio filters? 73, Darrell VA7TO K2 #5093 -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ 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 CW - Fundamental Keying Waveform?
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-----Original Message----- The recent thread on filter settings and hearing reminded me of a question I would like to get an answer to. In the ARRL 2001 Handbook on page 15.7 we find: "The dots and dashes of a CW signal must start and stop abruptly enough so we can clearly distinguish the carrier's presences and absences from noise, especially when fading prevails. The keying sidebands, which sound like little more than thumps when listened to on their own, help our brains be sure when the carrier tone starts and stops. It so happens that we always need to hear one or more harmonics of the fundamental keying waveform for the code to sound sufficiently crisp." What is meant by "the fundamental keying waveform"? How do we take "the need to hear one or more harmonics of the fundamental keying waveform" into account when setting up the IF and audio filters? 73, Darrell VA7TO K2 #5093 \------------------------------ The fundamental keying waveform is what you'd see if you monitored the keying voltage from your keyer on an oscilloscope, or looked at the dots and dashes of RF the transmitter produces. The carrier is keyed on and off sharply. That is, it rises from zero to maximum quickly at the start of each code element, then drops back to zero quickly at the end of the element. To do that requires a bandwidth much greater than the fundamental. Picture it this way. Look at the leading edge of one dit. Now construct a sine wave whose rise time matches the leading edge of the dit. Typically you will find that the frequency of such a sine wave will be in the range of 100 Hz or more. In that case, your cw transmitter will produce sidebands 100 Hz above and below the carrier frequency. When you key it, you are "amplitude modulating" the signal at the fundamental keying rate AND at the frequency defined by the steepness of the leading and trailing edges of the elements. For example, if you are transmitting at 7050 kHz (7050000 Hz) and the edges of the keying waveform has a shape corresponding to a 100 Hz sine wave, your transmitter will be producing a pulse of RF at 7050000.1 Hz and 7049000.9 Hz at the start and end of each code element. If your receiver bandpass does not allow that range of RF frequencies through, the keying waveform cannot be reproduced and the keying will sound soft. If the waveform is too sharp, those pulses (or clicks) will be widely separated from the carrier frequency - several hundred Hz or even more! That sharp of keying is never needed and only serves to produce QRM on the bands. But a reasonable amount of sideband energy is required for intelligible CW. Ron AC7AC _______________________________________________ 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 Darrell Bellerive
Darrell Bellerive wrote:
> What is meant by "the fundamental keying waveform"? I've wondered that myself. CW is made up of two separate periodic waveforms ... one is symmetric (the dits) and one is asymmetric (the dahs) and they occur in a more or less random sequence. For a given sending speed, each has a fundamental frequency: a dit is two elements in length, one on and one off. A dah is four elements in length, three on and one off. So, a string of dits is a square wave and the sidebands arise from the infinite series of sine wave harmonics, starting with the "dit rate" needed to construct a square wave. Likewise for a string of dahs, although the dah asymmetry would require a different coefficients in the infinite series of sine wave harmonics. I guess the dit and dah rates are low enough that some of those close in harmonics fall in a normal CW passband and we hear them. Of course, if we really do key with square waves, everyone else gets to hear all the others :-) Fred K6DGW Auburn CA CM98lw _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Darrell Bellerive
Ron, AC7AC wrote:
"The carrier is keyed on and off sharply. That is, it rises from zero to maximum quickly at the start of each code element, then drops back to zero quickly at the end of the element." ========== Not too quickly, or clicks will result. The K2 had quite bad clicks (+/-1500 Hz) until they developed a mod to cure that problem. K2 kits now include the mod, and they are among the most click-free of rigs today, with clicks extending only about +/-200 Hz from center freq. Icom IC-756 Pro IIs and IIIs have severe clicks extending +/-1500 Hz with the factory default risetime setting of "4 msec" (actually measured at 2 msec). Fortunately this is a user selectable menu setting and the rig's clicks are reduced to +/-400 HZ when the risetime is set to the max of "8 msec" (actually measure at 4 msec). The Yaesu MP series of rigs has been notorious for clicks extending +/-2500 Hz. The W8JI mod reduces the problem to +/-300 Hz. I understand that Yaesu fixed the problem (without fanfare) about a year ago on current production radios. The Ten-Tec Omni 6+ also has a bad click reputation (the Omni 6 non+ is click free).. In addition to fast rise/fall times (ARRL recommends a minimum of 4 msec to be click-free), the corners at the transitions should be rounded, rather than sharp. Most hams whose rigs have clicks are unaware of their problem because their casual QSOs are in relatively uncrowded bands. During contests however, when adjacent QSOs might be taking place only 500 Hz away, clicks heard outside of your receiver's passband are quite prevalent. This problem has abated somewhat in recent years because the ham community has been made aware of it via the many ham e-mail reflectors and many owners have performed click mods on their rigs. 73, de Earl, K6SE _______________________________________________ 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 CW - Fundamental Keying Waveform?
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Earl, K6SE wrote regarding keying:
Not too quickly, or clicks will result. The K2 had quite bad clicks (+/-1500 Hz) until they developed a mod to cure that problem. K2 kits now include the mod, and they are among the most click-free of rigs today, with clicks extending only about +/-200 Hz from center freq. ---------------------------- You missed the rest of that post. I wrote: "If the waveform is too sharp, those pulses (or clicks) will be widely separated from the carrier frequency - several hundred Hz or even more! That sharp of keying is never needed and only serves to produce QRM on the bands. But a reasonable amount of sideband energy is required for intelligible CW." Of course, we operate rigs with a great range of sophistication from modern rigs to hold homebrew one-tube oscillators that do a bit of "yooping" and clicking when keyed - and all of them are legal on the Ham bands. One of the things that characterize Amateur operations is just that, adapting, tinkering, building and experimenting with equipment that produces something far less than the theoretically possible level of performance while enjoying and learning from what we can do with it. Only a small percentage of the operators meet the "state of the art" limits in any arena with their rigs. What is unacceptable with regards to clicks is a matter of opinion. I'll seldom comment on clicks out to a KHz or so from the carrier, especially if it's an older design. I was never unhappy with the performance of the K2. I would never want to discourage anyone from wiring up a one or two stage transmitter or from firing up a 50 or 75 year old antique rig on the bands. To me, that's what Ham radio is really all about. Ron AC7AC _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Darrell Bellerive
Darrell,
That has ben dropped from the more recent handbook (does not appear in my 2005 edition). I am going 'out on a limb' here by saying that this stems from the concept that 'some keyclicks are good' philosophy. Sidebands on a CW signal are the result of the keying shape, and there is more to it than just the rise and fall times - there is the rounding at the corners to consider too. I have heard many an operator state that 'hard keying' will get you through a pile-up better. While that may be true, it certainly is not 'neighborly'. I am glad to see that this statement does not appear in the more recent handbooks. 73, Don W3FPR > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Darrell Bellerive > Sent: Tuesday, September 19, 2006 6:08 PM > To: Elecraft List > Subject: [Elecraft] Hearing CW - Fundamental Keying Waveform? > > > The recent thread on filter settings and hearing reminded me of a > question I > would like to get an answer to. > > In the ARRL 2001 Handbook on page 15.7 we find: > "The dots and dashes of a CW signal must start and stop > abruptly enough so > we can clearly distinguish the carrier's presences and absences > from noise, > especially when fading prevails. The keying sidebands, which sound like > little more than thumps when listened to on their own, help our brains be > sure when the carrier tone starts and stops. > It so happens that we always need to hear one or more harmonics of the > fundamental keying waveform for the code to sound sufficiently crisp." > > What is meant by "the fundamental keying waveform"? > > How do we take "the need to hear one or more harmonics of the fundamental > keying waveform" into account when setting up the IF and audio filters? > > 73, > > Darrell VA7TO K2 #5093 > > -- > Darrell Bellerive > Amateur Radio Stations VA7TO and VE7CLA > Grand Forks, British Columbia, Canada > _______________________________________________ > 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 Free Edition. > Version: 7.1.405 / Virus Database: 268.12.5/450 - Release Date: 9/18/2006 > > _______________________________________________ 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 CW - Fundamental Keying Waveform?
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Y'know what catches my ear, especially when a signal is very weak: chirp! A
little chirp stands out like nothing else to my hearing. And it's usually an interesting rig at the other end <G>. Any detectable chirp seems to drive some of today's ARRL "Official Observers" into near apoplexy but I enjoy hearing it! Y'know there was actually a time when a fellow could tune across a band, especially 80 or 40, and immediately recognize various stations by the keying characteristic of their rig and their fists on a mechanical key. Different stations had distinctively different voices. By comparison, listening on the ham bands today is rather like attending a party where everyone speaks with an identical artificial computer-produced "voice" <G> Ron AC7AC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Don Wilhelm Sent: Tuesday, September 19, 2006 9:32 PM To: [hidden email]; Elecraft List Subject: RE: [Elecraft] Hearing CW - Fundamental Keying Waveform? Darrell, That has ben dropped from the more recent handbook (does not appear in my 2005 edition). I am going 'out on a limb' here by saying that this stems from the concept that 'some keyclicks are good' philosophy. Sidebands on a CW signal are the result of the keying shape, and there is more to it than just the rise and fall times - there is the rounding at the corners to consider too. I have heard many an operator state that 'hard keying' will get you through a pile-up better. While that may be true, it certainly is not 'neighborly'. I am glad to see that this statement does not appear in the more recent handbooks. 73, Don W3FPR _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Darrell Bellerive
Ron, AC7AC wrote:
"You missed the rest of that post. I wrote" ========== No, I didn't miss any of the rest of your post. I merely commented further on the key click problems of today's modern rigs. BTW, Elecraft is the only manufacturer who admitted there was a click problem (a 3 kHz BW for a CW signal) with one of their products and they promptly did something to cure it (plus a multitude of other K2 improvements they did). 73, de Earl, K6SE _______________________________________________ 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 Ron D'Eau Claire-2
Ron D'Eau Claire wrote:
> Y'know there was actually a time when a fellow could tune across a band, > especially 80 or 40, and immediately recognize various stations by the > keying characteristic of their rig and their fists on a mechanical key. > Different stations had distinctively different voices. By comparison, > listening on the ham bands today is rather like attending a party where > everyone speaks with an identical artificial computer-produced "voice" <G> I recall traffic nets in which stations would initiate their check-in by sending a single element -- not a letter, just a single dit or dah. The NCS would immediately respond with the call! -- 73 Vic, K2VCO Fresno, CA http://www.qsl.net/k2vco _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Ron D'Eau Claire-2
On Tue, 19 Sep 2006, Ron D'Eau Claire wrote:
> > Y'know there was actually a time when a fellow could tune across a band, > especially 80 or 40, and immediately recognize various stations by the > keying characteristic of their rig and their fists on a mechanical key. > Different stations had distinctively different voices. By comparison, > listening on the ham bands today is rather like attending a party where > everyone speaks with an identical artificial computer-produced "voice" <G> THere was a time when you could find a neighborhood bakery...and in large cities, you could find ethnic neighborhoods with their own bakeries, groceries, and churches. There was also a time when you could find solid wood furnature that was affordable....or restaurants that didn't buy pre-cooked meals from a vendor. With all the improvements in today's world, we seem to have lost a lot of the personality and flavor of many things. I'm happy to be able to remember recognizing a station by the sound of the cw note and the fist of the operator.... I'm tempted to jot down Hal as the name of many guys I work...the same note, the same fist. Perhaps it's time to add some more items to http://www.zerobeat.net/qrp/qrpretro.html 73,Thom-k3hrn www.zerobeat.net Home of QRP Web Ring, Drakelist home page,Drake Web Ring, QRP IRC channel, Drake IRC Channel, Elecraft Owners Database www.tlchost.net/hosting/ *** Web Hosting as low as 3.49/month _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Darrell Bellerive
Hmm,
> Any detectable chirp seems to drive some of today's ARRL "Official > Observers" into near apoplexy but I enjoy hearing it! That's interesting. Which FCC or ARRL guideline mentions chirp, or otherwise attempts to regulate the keying waveform? I had a look through our Canadian guidelines: RIC 2 - Standards for the Operation of Radio Stations in the Amateur Radio Service I can't find anything about chirp, although there is a clause about frequency stability, and I suppose that chirp could be defined as frequency stability over a period of time equivalent to a code element. But I rather think that it means drift and not chirp. So - as long as I keep to 6kHz bandwitdh and 1kHz on 30m, then it looks like I'm allowed to have chirp on my signal. Now where do I need to solder a small cap on the KX1 to introduce some nice distinctive chirp on my signal?... 73 Martin. VA3SIE. _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Don Wilhelm-3
This discussion is very interesting to me. I hate copying stations
whose keying isn't sharp enough. The dits and dahs seem to blend together. It seems to me that with all the DSP power that modern rigs have, there should be a way to "sharpen up" a CW signal to make it more intelligible. I'm copying this message to my friend VU3RDD, who is a DSP engineer, to see what he might think about this. 73! Dan KB6NU ---------------------------------------------------------- CW Geek and MI Affiliated Club Coordinator Read my ham radio blog at www.kb6nu.com LET'S GET MORE KIDS INTO HAM RADIO! On Sep 20, 2006, at 12:31 AM, Don Wilhelm wrote: > Darrell, > > That has ben dropped from the more recent handbook (does not appear > in my > 2005 edition). > I am going 'out on a limb' here by saying that this stems from the > concept > that 'some keyclicks are good' philosophy. Sidebands on a CW > signal are the > result of the keying shape, and there is more to it than just the > rise and > fall times - there is the rounding at the corners to consider too. > > I have heard many an operator state that 'hard keying' will get you > through > a pile-up better. While that may be true, it certainly is not > 'neighborly'. > > I am glad to see that this statement does not appear in the more > recent > handbooks. > > 73, > Don W3FPR > > >> -----Original Message----- >> From: [hidden email] >> [mailto:[hidden email]]On Behalf Of Darrell >> Bellerive >> Sent: Tuesday, September 19, 2006 6:08 PM >> To: Elecraft List >> Subject: [Elecraft] Hearing CW - Fundamental Keying Waveform? >> >> >> The recent thread on filter settings and hearing reminded me of a >> question I >> would like to get an answer to. >> >> In the ARRL 2001 Handbook on page 15.7 we find: >> "The dots and dashes of a CW signal must start and stop >> abruptly enough so >> we can clearly distinguish the carrier's presences and absences >> from noise, >> especially when fading prevails. The keying sidebands, which sound >> like >> little more than thumps when listened to on their own, help our >> brains be >> sure when the carrier tone starts and stops. >> It so happens that we always need to hear one or more harmonics >> of the >> fundamental keying waveform for the code to sound sufficiently >> crisp." >> >> What is meant by "the fundamental keying waveform"? >> >> How do we take "the need to hear one or more harmonics of the >> fundamental >> keying waveform" into account when setting up the IF and audio >> filters? >> >> 73, >> >> Darrell VA7TO K2 #5093 >> >> -- >> Darrell Bellerive >> Amateur Radio Stations VA7TO and VE7CLA >> Grand Forks, British Columbia, Canada 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 Martin Gillen-2
At 09:13 AM 9/20/2006, Martin Gillen wrote...
>Which FCC or ARRL guideline mentions chirp, or otherwise attempts to >regulate the keying waveform? 97.307(a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice. (b) Emissions resulting from modulation must be confined to the band or segment available to the control operator. Emissions outside the necessary bandwidth must not cause splatter or keyclick interference to operations on adjacent frequencies. (c) All spurious emissions from a station transmitter must be reduced to the greatest extent practicable. If any spurious emission, including chassis or power line radiation, causes harmful interference to the reception of another radio station, the licensee of the interfering amateur station is required to take steps to eliminate the interference, in accordance with good engineering practice. And it continues on with regard to specific standards and measurements of spurious emissions. _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Martin Gillen-2
As long as we are discussing hearing cw I'd like to ask a question that has
been bothering me for many years. I am very sensitive to chirp, and that is not what I am referring to. When I listen to a good cw signal in the range of about 20-35 wpm I heard the dots and dashes as at slightly different frequencies. This may simply be some sort of psychological quirk unique to me. I am not even sure "slightly different frequencies" or tones is correct way to describe it. Realizing that I am not listening to a sinusoidal tone but sequences of short and long symbols and that long strings of dots will have wider sidebands than long strings of dashes, I wonder if this is relevant in any way. Most likely it is some sort of personal quirk. But I wonder if anyone on this reflector by any chance notices anything similar or has an explanation? Bob W2WG -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Martin Gillen Sent: Wednesday, September 20, 2006 9:13 AM To: elecraft Subject: RE: [Elecraft] Hearing CW - Fundamental Keying Waveform? Hmm, > Any detectable chirp seems to drive some of today's ARRL "Official > Observers" into near apoplexy but I enjoy hearing it! That's interesting. Which FCC or ARRL guideline mentions chirp, or otherwise attempts to regulate the keying waveform? I had a look through our Canadian guidelines: RIC 2 - Standards for the Operation of Radio Stations in the Amateur Radio Service I can't find anything about chirp, although there is a clause about frequency stability, and I suppose that chirp could be defined as frequency stability over a period of time equivalent to a code element. But I rather think that it means drift and not chirp. So - as long as I keep to 6kHz bandwitdh and 1kHz on 30m, then it looks like I'm allowed to have chirp on my signal. Now where do I need to solder a small cap on the KX1 to introduce some nice distinctive chirp on my signal?... 73 Martin. VA3SIE. _______________________________________________ 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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In reply to this post by Dan Romanchik KB6NU
Dan KB6NU wrote:
> This discussion is very interesting to me. I hate copying stations whose > keying isn't sharp enough. The dits and dahs seem to blend together. It > seems to me that with all the DSP power that modern rigs have, there > should be a way to "sharpen up" a CW signal to make it more > intelligible. Modern rigs all have rise/fall times between about 2 ms. (which produces a quite clicky and too-broad signal) and about 8 ms. I think the current K2 is maybe 5 or 6 ms. At keying speeds below about 50 wpm, there should be absolutely no problem with the elements seeming to blend together. Also keep in mind that regardless of the actual rise/fall times of the signal, high selectivity (< about 500 Hz.) starts to noticeably soften what you hear. There are schemes that regenerate a CW signal (basically, use the received signal to key a local oscillator or it's possible to simply clip a signal if the s/n ratio is reasonable in order to sharpen it up. But this doesn't seem to be especially helpful at the usual speeds. I'm not sure what characteristic you're describing that makes CW hard to copy, but I don't think it's the shape of the keyed envelope. -- 73 Vic, K2VCO Fresno, CA http://www.qsl.net/k2vco _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Dan Romanchik KB6NU
Thanks Dan for copying me. I just subscribed to the list.
The issue is discussed at length by Doug Smith, who is also the Editor of ARRL's QEX. http://www.doug-smith.net/cwbandwidth1.htm In the digital communication world, we have a baseband modulation scheme called Pulse Amplitude modulation (PAM), which is one of the simplest form of modulation. CW can be thought of as one form of PAM. To avoid Inter Symbol Interference (ISI), the pulse shape used in the PAM scheme should have certain properties. Key Clicks are nothing but abrupt changes in the waveform, which interferes with the neighbouring pulse shapes, which is ISI. The Sinc Pulse is one such waveform, but is difficult to synthesize in real world. Another such pulseshape which satisfies this is the Raised Cosine waveform. http://en.wikipedia.org/wiki/Raised-cosine_filter Another variant is the square root of raised cosine shape, where transmitter and reciever both use a square root of the above filter response in (frequency domain) and when you convolve them together in time domain you get the raise cosine response. I think I have complicated it too much. :-( The above links explain it in a much better way. This is the basic principle behind it, but there are many refinements. Ramakrishnan, VU3RDD On 9/20/06, Dan KB6NU <[hidden email]> wrote: > This discussion is very interesting to me. I hate copying stations > whose keying isn't sharp enough. The dits and dahs seem to blend > together. It seems to me that with all the DSP power that modern rigs > have, there should be a way to "sharpen up" a CW signal to make it > more intelligible. I'm copying this message to my friend VU3RDD, who > is a DSP engineer, to see what he might think about this. > > 73! > > Dan KB6NU > ---------------------------------------------------------- > CW Geek and MI Affiliated Club Coordinator > Read my ham radio blog at www.kb6nu.com > LET'S GET MORE KIDS INTO HAM RADIO! > > > On Sep 20, 2006, at 12:31 AM, Don Wilhelm wrote: > > Darrell, > > > > That has ben dropped from the more recent handbook (does not appear > > in my > > 2005 edition). > > I am going 'out on a limb' here by saying that this stems from the > > concept > > that 'some keyclicks are good' philosophy. Sidebands on a CW > > signal are the > > result of the keying shape, and there is more to it than just the > > rise and > > fall times - there is the rounding at the corners to consider too. > > > > I have heard many an operator state that 'hard keying' will get you > > through > > a pile-up better. While that may be true, it certainly is not > > 'neighborly'. > > > > I am glad to see that this statement does not appear in the more > > recent > > handbooks. > > > > 73, > > Don W3FPR > > > > > >> -----Original Message----- > >> From: [hidden email] > >> [mailto:[hidden email]]On Behalf Of Darrell > >> Bellerive > >> Sent: Tuesday, September 19, 2006 6:08 PM > >> To: Elecraft List > >> Subject: [Elecraft] Hearing CW - Fundamental Keying Waveform? > >> > >> > >> The recent thread on filter settings and hearing reminded me of a > >> question I > >> would like to get an answer to. > >> > >> In the ARRL 2001 Handbook on page 15.7 we find: > >> "The dots and dashes of a CW signal must start and stop > >> abruptly enough so > >> we can clearly distinguish the carrier's presences and absences > >> from noise, > >> especially when fading prevails. The keying sidebands, which sound > >> like > >> little more than thumps when listened to on their own, help our > >> brains be > >> sure when the carrier tone starts and stops. > >> It so happens that we always need to hear one or more harmonics > >> of the > >> fundamental keying waveform for the code to sound sufficiently > >> crisp." > >> > >> What is meant by "the fundamental keying waveform"? > >> > >> How do we take "the need to hear one or more harmonics of the > >> fundamental > >> keying waveform" into account when setting up the IF and audio > >> filters? > >> > >> 73, > >> > >> Darrell VA7TO K2 #5093 > >> > >> -- > >> Darrell Bellerive > >> Amateur Radio Stations VA7TO and VE7CLA > >> Grand Forks, British Columbia, Canada > -- Ramakrishnan - VU3RDD _______________________________________________ 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 CW - Fundamental Keying Waveform?
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For the mathematically inclined, here is another link:
http://fermi.la.asu.edu/w9cf/articles/click/index.html Ramakrishnan On 9/20/06, Ramakrishnan Muthukrishnan <[hidden email]> wrote: > Thanks Dan for copying me. I just subscribed to the list. > > The issue is discussed at length by Doug Smith, who is also the Editor > of ARRL's QEX. > > http://www.doug-smith.net/cwbandwidth1.htm > > In the digital communication world, we have a baseband modulation > scheme called Pulse Amplitude modulation (PAM), which is one of the > simplest form of modulation. CW can be thought of as one form of PAM. > To avoid Inter Symbol Interference (ISI), the pulse shape used in the > PAM scheme should have certain properties. Key Clicks are nothing but > abrupt changes in the waveform, which interferes with the neighbouring > pulse shapes, which is ISI. The Sinc Pulse is one such waveform, but > is difficult to synthesize in real world. Another such pulseshape > which satisfies this is the Raised Cosine waveform. > > http://en.wikipedia.org/wiki/Raised-cosine_filter > > Another variant is the square root of raised cosine shape, where > transmitter and reciever both use a square root of the above filter > response in (frequency domain) and when you convolve them together in > time domain you get the raise cosine response. > > I think I have complicated it too much. :-( The above links explain > it in a much better way. > > This is the basic principle behind it, but there are many refinements. > > Ramakrishnan, VU3RDD > > On 9/20/06, Dan KB6NU <[hidden email]> wrote: > > This discussion is very interesting to me. I hate copying stations > > whose keying isn't sharp enough. The dits and dahs seem to blend > > together. It seems to me that with all the DSP power that modern rigs > > have, there should be a way to "sharpen up" a CW signal to make it > > more intelligible. I'm copying this message to my friend VU3RDD, who > > is a DSP engineer, to see what he might think about this. > > > > 73! > > > > Dan KB6NU > > ---------------------------------------------------------- > > CW Geek and MI Affiliated Club Coordinator > > Read my ham radio blog at www.kb6nu.com > > LET'S GET MORE KIDS INTO HAM RADIO! > > > > > > On Sep 20, 2006, at 12:31 AM, Don Wilhelm wrote: > > > Darrell, > > > > > > That has ben dropped from the more recent handbook (does not appear > > > in my > > > 2005 edition). > > > I am going 'out on a limb' here by saying that this stems from the > > > concept > > > that 'some keyclicks are good' philosophy. Sidebands on a CW > > > signal are the > > > result of the keying shape, and there is more to it than just the > > > rise and > > > fall times - there is the rounding at the corners to consider too. > > > > > > I have heard many an operator state that 'hard keying' will get you > > > through > > > a pile-up better. While that may be true, it certainly is not > > > 'neighborly'. > > > > > > I am glad to see that this statement does not appear in the more > > > recent > > > handbooks. > > > > > > 73, > > > Don W3FPR > > > > > > > > >> -----Original Message----- > > >> From: [hidden email] > > >> [mailto:[hidden email]]On Behalf Of Darrell > > >> Bellerive > > >> Sent: Tuesday, September 19, 2006 6:08 PM > > >> To: Elecraft List > > >> Subject: [Elecraft] Hearing CW - Fundamental Keying Waveform? > > >> > > >> > > >> The recent thread on filter settings and hearing reminded me of a > > >> question I > > >> would like to get an answer to. > > >> > > >> In the ARRL 2001 Handbook on page 15.7 we find: > > >> "The dots and dashes of a CW signal must start and stop > > >> abruptly enough so > > >> we can clearly distinguish the carrier's presences and absences > > >> from noise, > > >> especially when fading prevails. The keying sidebands, which sound > > >> like > > >> little more than thumps when listened to on their own, help our > > >> brains be > > >> sure when the carrier tone starts and stops. > > >> It so happens that we always need to hear one or more harmonics > > >> of the > > >> fundamental keying waveform for the code to sound sufficiently > > >> crisp." > > >> > > >> What is meant by "the fundamental keying waveform"? > > >> > > >> How do we take "the need to hear one or more harmonics of the > > >> fundamental > > >> keying waveform" into account when setting up the IF and audio > > >> filters? > > >> > > >> 73, > > >> > > >> Darrell VA7TO K2 #5093 > > >> > > >> -- > > >> Darrell Bellerive > > >> Amateur Radio Stations VA7TO and VE7CLA > > >> Grand Forks, British Columbia, Canada > > > > > -- > Ramakrishnan - VU3RDD > -- Ramakrishnan - VU3RDD _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Mike S-8
On 9/20/2006 at 3:03 PM, Mike W8UR wrote:
> 97.307(a) No amateur station transmission shall occupy more bandwidth than > necessary for the information rate and emission type being transmitted, in > accordance with good amateur practice. > > (b) Emissions resulting from modulation must be confined to the band or > segment available to the control operator. Emissions outside the necessary > bandwidth must not cause splatter or keyclick interference to operations > on adjacent frequencies. <snip> ---------------------------------------------------------------------------- To digress to SSB for a moment, (a) means IMHO that the *necessary* bandwidth should not be greater than 2.2 kHz for voice. Very good 'smooth sounding' and effective voice SSB can be produced using a filter of this bandwidth. Sorry for the digression. 73, Geoff GM4ESD _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by ROBERT CARROLL-4
Bob:
As you correctly note, a CW signal is not a pure sinusoid. The Fourier spectrum of an individual dot or dash is a distribution of frequencies with a peak at the "dead carrier" frequency. There is an inverse relationship between the width of a pulse in the time domain and the width of its Fourier spectrum. This is no surprise. A dash is a closer approximation of a "dead carrier" than a dot, and consequently has more of its energy concentrated closer to the peak of the spectrum. At higher speeds, the dots and dashes would have broader spectra than at lower speeds. (That is why EME operators achieve extreme noise reduction by using audio filters on the order of 10 Hz and transmitting at 2-3 WPM.) Thus, I expect that the higher the code speed, the more likely that the distinction in the specta of dots and dashes would be discernable to human sensibilities. In cognitive processing of sensory data, the brain functions a differencing engine. Each brain has a capability of distinguishing audible spectra, but some are more sensitive to particular nuances of difference than others. Apparently, your hearing is more sensitive than normal to the nuances of difference between dots and dashes. As you have guessed, you are not hearing "slightly different frequencies." You are experiencing the dot and dash spectra as two distinctly different Gestalts. In other words, you are hearing two slightly different frequency distributions as two distinct whole events. Your experience seems somewhat akin to the small group of women (it never happens in men) who have four sets of rods and cones in their retinas. These women do not actually see a color invisible to the rest of us. What they do see is the subtle distinction in shades of color that the rest of us are incapable of noticing. 73, Steve AA4AK At 10:11 AM 9/20/2006, Robert Carroll wrote: >As long as we are discussing hearing cw I'd like to ask a question that has >been bothering me for many years. I am very sensitive to chirp, and that is >not what I am referring to. When I listen to a good cw signal in the range >of about 20-35 wpm I heard the dots and dashes as at slightly different >frequencies. This may simply be some sort of psychological quirk unique to >me. I am not even sure "slightly different frequencies" or tones is correct >way to describe it. Realizing that I am not listening to a sinusoidal tone >but sequences of short and long symbols and that long strings of dots will >have wider sidebands than long strings of dashes, I wonder if this is >relevant in any way. Most likely it is some sort of personal quirk. But I >wonder if anyone on this reflector by any chance notices anything similar or >has an explanation? > >Bob W2WG _______________________________________________ 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 CW - Fundamental Keying Waveform?
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In reply to this post by Darrell Bellerive
Wow, I never thought my question would spur on such a discussion!
So, if I understand correctly we have three components in the transmitted CW signal that affect what we hear on our receivers: 1) The carrier and it's stability in frequency, 2) the actual keying on and off of the carrier, and 3) the shape of the leading and trailing edge of the keying. Also, as the receive bandwidth in narrowed, the result is a "softer" sound to the keying. Our hearing may also detect the differences in the audio frequency component distribution present between the dots and dashes themselves. In other words, dots may sound harder than dashes. So, assuming that the above transmit parameters are nominal for the amateur service, can the IF and AF filters in the receiver be adjusted to enhance or reduce the effects of the shape of the keying waveform? As stated above, the width of the bandwidth determines the softness, but what about shifting the bandwidth above or below the carrier beatnote? What about changing the slope or flatness of the bandwidth? I've always set my K2 filters so that the carrier beatnote is in the center of the the bandpass. If the bandpass is offset so that the carrier beatnote is at either the high or low end of the bandpass, yet still within the flat part of the bandwidth, what will be the effect on the way we hear the CW? Will we hear a harder note for the same bandwidth? Darrell VA7TO K2#5093 On September 19, 2006 03:07 pm, Darrell Bellerive wrote: > What is meant by "the fundamental keying waveform"? -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ 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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