VP6DX -- the true story ?
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Hi,
besides the "official" report as quoted on the web, on the BCC mailing list, reports from members of the VP6DX expedition were slightly less stellar. While confirming superior receiver sensitivity, problems reported were with pileup CW reception & AGC, in T/R switching, and internal noise of S9+20 that went away after powercycling the K3 ??? Since I've just ordered my K3, I'd like to hear whether this has been confirmed, and hopefully fixed... Mario -- Mario Lorenz Internet: <[hidden email]> Ham Radio: DL5MLO@DB0ERF.#THR.DEU.EU * Newsflash: Microsoft announces Visual Edlin for Windows98! _______________________________________________ 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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Scandalous rumour - I think you'd have seen if S9+ noise was occurring
On 10/03/2008 13:50, "Mario Lorenz" <[hidden email]> sent: > Hi, > > besides the "official" report as quoted on the web, > on the BCC mailing list, reports from members of the VP6DX > expedition were slightly less stellar. > > While confirming superior receiver sensitivity, problems reported > were with pileup CW reception & AGC, in T/R switching, > and internal noise of S9+20 that went away after powercycling > the K3 ??? > > Since I've just ordered my K3, I'd like to hear whether this has > been confirmed, and hopefully fixed... > > Mario -- God gives every bird his worm, but he does not throw it into the nest. -Swedish proverb _______________________________________________ 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: VP6DX -- the true story ?
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In reply to this post by Mario Lorenz
Some reported hiccups with the radios should be put into perspective:
1. We ran 8 radios x 24 hours x 16+ days of operating: over 3,000 hours on the air in total... plus additional hours for some units on board ship. 2. Some glitches were unique a specific radio, or at most two radios. As an example, late in the operation one radio seemed to show a T/R relay problem where the receiver signals were down temporarily (or longer) after a transmission. Another radio didn't want to power off -- it would immediately come back to life after shutdown. The "high noise level" was another singleton issue. One radio, only on 30m, and only while in FSK mode, and only when operating split, would have its receiver go into oscillation at the end of a FSK transmission. If any one of those three conditions did not exist, the radio worked fine. Obviously we moved that radio away from the position with the 30m 4-square antenna control. We didn't see that particular quirk on any other radio. 3. We were operating in a demanding field environment: hot temperatures in the tents during the day, salty and dusty breezes almost non-stop, and perhaps some voltage burbles when the generators ran out of fuel unexpectedly. On the later point, we did have sealed batteries floated across the supply lines, which allowed us to continue operating (without the 1.5 kW amplifiers) when generator re-fueling or oil changes were made. Those certainly helped smooth out any power supply variations. 4. Some items were equipment interaction issues. For example, our CW keying (external to the K3) sometimes hung. We learned this was due to RFI entering the laptop USB port via the external mouse cable, and irritating the USB device driver for the microKeyer and/or the microKeyer. Almost all of the operators ran the K3 with AGC off (all modes). -- Eric on 08 Mar 10 Mon 09:50 Mario Lorenz said the following: > Hi, > > besides the "official" report as quoted on the web, > on the BCC mailing list, reports from members of the VP6DX > expedition were slightly less stellar. > > While confirming superior receiver sensitivity, problems reported > were with pileup CW reception & AGC, in T/R switching, > and internal noise of S9+20 that went away after powercycling > the K3 ??? > > Since I've just ordered my K3, I'd like to hear whether this has > been confirmed, and hopefully fixed... > > Mario > > 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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You can't get much better than that, Eric!!
I identified (whilst working VP6DX!) a similar situation to the 30m one. It was as though the PLL wasn't locking. I don't do data modes so mine was 30m CW Split. I emailed Gary at Elecraft and a mod was incorporated in the next firmware upgrade, and it is perfect now. Excellent service BTW, I worked all of my 12 band slots on the K3 using Split and pressing Rev to listen to the awful Eu pile-up. The whole experience would have been so much less stressful if European stations were more discipliined. If he calls HB9 then why does a DL, SP, IZ, 9A or whatever transmit?!! Thanks. Chris G3SJJ Eric Scace K3NA wrote: > Some reported hiccups with the radios should be put into perspective: > > 1. We ran 8 radios x 24 hours x 16+ days of operating: over 3,000 > hours on the air in total... plus additional hours for some units on > board ship. > > 2. Some glitches were unique a specific radio, or at most two > radios. As an example, late in the operation one radio seemed to show > a T/R relay problem where the receiver signals were down temporarily > (or longer) after a transmission. Another radio didn't want to power > off -- it would immediately come back to life after shutdown. > The "high noise level" was another singleton issue. One radio, only > on 30m, and only while in FSK mode, and only when operating split, > would have its receiver go into oscillation at the end of a FSK > transmission. If any one of those three conditions did not exist, the > radio worked fine. Obviously we moved that radio away from the > position with the 30m 4-square antenna control. We didn't see that > particular quirk on any other radio. > > 3. We were operating in a demanding field environment: hot > temperatures in the tents during the day, salty and dusty breezes > almost non-stop, and perhaps some voltage burbles when the generators > ran out of fuel unexpectedly. > On the later point, we did have sealed batteries floated across the > supply lines, which allowed us to continue operating (without the 1.5 > kW amplifiers) when generator re-fueling or oil changes were made. > Those certainly helped smooth out any power supply variations. > > 4. Some items were equipment interaction issues. For example, our CW > keying (external to the K3) sometimes hung. We learned this was due > to RFI entering the laptop USB port via the external mouse cable, and > irritating the USB device driver for the microKeyer and/or the > microKeyer. > > Almost all of the operators ran the K3 with AGC off (all modes). > > -- Eric > > > > on 08 Mar 10 Mon 09:50 Mario Lorenz said the following: >> Hi, >> >> besides the "official" report as quoted on the web, >> on the BCC mailing list, reports from members of the VP6DX >> expedition were slightly less stellar. >> >> While confirming superior receiver sensitivity, problems reported >> were with pileup CW reception & AGC, in T/R switching, and internal >> noise of S9+20 that went away after powercycling >> the K3 ??? >> >> Since I've just ordered my K3, I'd like to hear whether this has >> been confirmed, and hopefully fixed... >> >> Mario >> >> > _______________________________________________ > 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 Eric Scace K3NA
> Almost all of the operators ran the K3 with AGC off (all modes).
> > -- Eric Eric, can you explain what did you not like about AGC in K3? Did you notice any problems with DSP being permanently on in K3 when listening to heavy pile ups? 73, Igor UA9CDC _______________________________________________ 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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>> Almost all of the operators ran the K3 with AGC off (all modes).
> Eric, can you explain what did you not like about AGC in K3? Also which version of the firmware was installed while on VP6D would be interesting. I believe than Wayne and Lyle have been making changes, but personally I've been fairly happy with the default AGC up to now. vy 73 de toby _______________________________________________ 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 Mario Lorenz
Dear Igor & Others,
May I speculate? Any AGC compresses the dynamic range of incoming signals. AGC means Automatic Gain Control. If you had an invisible hand that would adjust the RF gain control for you, that is what AGC does. When you are working many stations on the same frequency and they are very close to zero beat turning off the AGC creates a greater dynamic range in the ear of the receiving operator and thus gives an additional tool to separate the signals. When I was a commercial operator at KPH, nearly all the operators ran AGC off all the time. It makes the QRM/QRN fade away. TR, WB6TMY Message: 56 Date: Thu, 13 Mar 2008 11:26:32 +0500 From: "Igor Sokolov" <[hidden email]> Subject: Re: [Elecraft] VP6DX -- the true story ? > Almost all of the operators ran the K3 with AGC off (all modes). > > -- Eric Eric, can you explain what did you not like about AGC in K3? Did you notice any problems with DSP being permanently on in K3 when listening to heavy pile ups? 73, Igor UA9CDC _______________________________________________ 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: VP6DX -- the true story ?
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In reply to this post by Igor Sokolov-2
Privet Igor --
As best I can remember, we used MCU v1.66 and DSP 1.52. I didn't use the AGC because I did not need it. The point of automatic gain control is to adjust the gain of the various stages of the receiver in order to a) avoid distortion/overdriving a stage, and b) bring signals up/down to a comfortable listening level. (b) is not relevant to an operator who is working a pileup. (b) is relevant to an operator who is monitoring a frequency with one station transmitting. For operating a pileup, there are a variety of tools the brain uses to distinguish the many signals: -- pitch (CW) -- style of speaking (speech) or keying (CW) -- artifacts; e.g., auroral flutter, chirp, etc. -- strength (all). AGC tends to reduce the difference in signal strength, and so removed valuable information. In situations where static crashes interfere with reception, AGC hang time on a loud static crash also increases the length of time that a specific static crash interferes with reception. I used headphones with good audio isolation between my ears and the rest of the world around me. That allows me to set receiver gain levels with the underlying antenna/band noise just above my threshold of hearing... and to use at least 80 dB of my hearing range for listening. In this quiet listening environment, I don't need AGC. Even in a less-than-quiet listening environment, if a band is just open weakly (e.g., 12m to Europe), the range of signal strengths in the pileup can be smaller: maybe less than 30 dB between band noise and the strongest signal. So AGC isn't needed here either. My ideal AGC in these situations is one that only makes changes in receiver gain when a stage in the receiver is about to be over-driven (e.g., the A/D converter)... and removes those changes relatively quickly. Even then, it might be fine to allow the receiver to be over-driven (a static crash contains no information). If a signal I want to copy is over-driving the receiver, the best solution often is to reduce the RF gain manually during the duration of the time when I want to copy that station. If that station is just "interference" (e.g., a loud USA station on 80m CW calling VP6DX, when I want to work northern Scandinavia and northwest Russia/western Asia during the brief opening), I have other controls (filter bandwidth, notch) than might be better to use that gain reduction (automatic or manual) that could suppress the desired weak signals. So, almost any AGC system is inappropriate for a DXpedition or content environment... as long as the receiver and one's own ears have enough dynamic range to handle all the signals presented to it. The K3 has more dynamic range than other receivers. 73, -- Eric K3NA on 08 Mar 13 Thu 02:26 Igor Sokolov said the following: >> Almost all of the operators ran the K3 with AGC off (all modes). >> >> -- Eric > > Eric, can you explain what did you not like about AGC in K3? > Did you notice any problems with DSP being permanently on in K3 when > listening to heavy pile ups? > > 73, Igor UA9CDC > 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 TR K2 #838
Another one that Fred K3ZO (many time winner of Dayton CW pileup contests) recently mentioned is using extremely low pitch for weak signals. Fred said many commercial ops he knew used somewhere in the 2-300 Hz range so he thought his favored 400 Hz was rather high! I discovered this myself many years ago using the TS-930S which had a continuously adjustable pitch control down to zero! I found 240-270 Hz worked well for weak signals buried in noise on 160m. My hearing is excellent at all frequencies so this is not an issue of hearing loss but simply something I discovered works well for me. Low pitch does not work well for pileups or contests where there are many signals. For those I prefer 400-450 to better catch off-frequency callers, and shift 150-200 Hz on the low side of the center of the passband. Then I can hear most callers pitched at 200 Hz and up. Another thing K3ZO does is to use a wide filter (~1 kHz) and let his ears' 50 Hz DSP filter do the work. I haven't yet mastered that in a contest like the CQ 160! I'm getting by with the K3's lower pitch limit of 300 Hz but hoping for lower some day! 73, Bill W4ZV P.S. Any others...especially from ex-commercial ops? |
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I found the exact quote from Fred which was on the PVRC reflector: "With a rig like the Orion the tone you set your sidetone monitor to is also very important. I like to copy CW at 400 Hz, and I have been surprised when people have commented that 400 Hz is a much lower tone than they like to use. I believe it is established science that the lower the tone you use to copy, the better your ear is at separating out tones which differ in frequency very little from each other. I actually thought I was using a rather high choice of tone, as I recall some articles I read years ago, perhaps by professional ship-to-shore ops, advocating 200 or 300 Hz as their tones of choice." 73, Bill W4ZV |
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This makes perfect sense. The ears have a logarithmic response to sound
pressure and to frequency. David G3UNA >> >> >> Another one that Fred K3ZO (many time winner of Dayton CW pileup >> contests) >> recently mentioned is using extremely low pitch for weak signals. Fred >> said many commercial ops he knew used somewhere in the 2-300 Hz range so >> he thought his favored 400 Hz was rather high! >> > 73, Bill W4ZV > 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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400 Hz is my upper limit as well.
Lower than 300 Hz is certainly desirable to me. I have forty plus years on CW, and no significant hearing loss. I do the between-the-headphones DSP far more effectively at 400 Hz and below. 73, john WA1ABI > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of David Cutter > Sent: Thursday, March 13, 2008 2:17 PM > To: Bill W4ZV; [hidden email] > Subject: Re: [Elecraft] CW Secrets of the Masters > > > This makes perfect sense. The ears have a logarithmic response to sound > pressure and to frequency. > > David > G3UNA > > >> > >> > >> Another one that Fred K3ZO (many time winner of Dayton CW pileup > >> contests) > >> recently mentioned is using extremely low pitch for weak signals. Fred > >> said many commercial ops he knew used somewhere in the 2-300 > Hz range so > >> he thought his favored 400 Hz was rather high! > >> > > 73, Bill W4ZV > > > _______________________________________________ > 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 Eric Scace K3NA
Thanks Eric,
I understand you think AGC in high dynamic range radio like K3 is not a necessity for the op with high dynamic range ears. Actually the range should be close to 90-95 db on nowadays bands where 59+40 signals co-exist with 1S unit signals very often. I also figured from your post that other ops from VP6DX team choose not to use AGC not because of some sort of problem existed in that version of the firmware but purely because they prefer adjusting RF gain manually to squeeze out the most from the pile up. What about the DSP then. I experienced that myself operating from 8Q7 in the past and many others confirmed my impressions that modern DSP based radios are no good when pulling call signs from the pile up of many stations when the average level of that pileup is close to the MDS of the radio. For example we could not use Orion in the expedition on a weak pile up on 10 and 15 meters while the same operators could easily pick out calls using IC775. Therefore I would be happy to have a radio where DSP could be switched on or off depending on the situation. Did you notice the above mentioned effect while using K3? 73, Igor UA9CDC > Privet Igor -- > > As best I can remember, we used MCU v1.66 and DSP 1.52. > > I didn't use the AGC because I did not need it. The point of automatic > gain control is to adjust the gain of the various stages of the receiver > in order to > a) avoid distortion/overdriving a stage, and > b) bring signals up/down to a comfortable listening level. > > (b) is not relevant to an operator who is working a pileup. (b) is > relevant to an operator who is monitoring a frequency with one station > transmitting. > > For operating a pileup, there are a variety of tools the brain uses to > distinguish the many signals: > -- pitch (CW) > -- style of speaking (speech) or keying (CW) > -- artifacts; e.g., auroral flutter, chirp, etc. > -- strength (all). > AGC tends to reduce the difference in signal strength, and so removed > valuable information. > > In situations where static crashes interfere with reception, AGC hang > time on a loud static crash also increases the length of time that a > specific static crash interferes with reception. > > I used headphones with good audio isolation between my ears and the rest > of the world around me. That allows me to set receiver gain levels with > the underlying antenna/band noise just above my threshold of hearing... > and to use at least 80 dB of my hearing range for listening. In this > quiet listening environment, I don't need AGC. > > Even in a less-than-quiet listening environment, if a band is just open > weakly (e.g., 12m to Europe), the range of signal strengths in the pileup > can be smaller: maybe less than 30 dB between band noise and the strongest > signal. So AGC isn't needed here either. > > My ideal AGC in these situations is one that only makes changes in > receiver gain when a stage in the receiver is about to be over-driven > (e.g., the A/D converter)... and removes those changes relatively quickly. > Even then, it might be fine to allow the receiver to be over-driven (a > static crash contains no information). If a signal I want to copy is > over-driving the receiver, the best solution often is to reduce the RF > gain manually during the duration of the time when I want to copy that > station. If that station is just "interference" (e.g., a loud USA station > on 80m CW calling VP6DX, when I want to work northern Scandinavia and > northwest Russia/western Asia during the brief opening), I have other > controls (filter bandwidth, notch) than might be better to use that gain > reduction (automatic or manual) that could suppress the desired weak > signals. > > So, almost any AGC system is inappropriate for a DXpedition or content > environment... as long as the receiver and one's own ears have enough > dynamic range to handle all the signals presented to it. The K3 has more > dynamic range than other receivers. > > 73, > -- Eric K3NA > > on 08 Mar 13 Thu 02:26 Igor Sokolov said the following: >>> Almost all of the operators ran the K3 with AGC off (all modes). >>> >>> -- Eric >> >> Eric, can you explain what did you not like about AGC in K3? >> Did you notice any problems with DSP being permanently on in K3 when >> listening to heavy pile ups? >> >> 73, Igor UA9CDC >> _______________________________________________ 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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Igor Sokolov wrote:
> What about the DSP then. I experienced that myself operating from 8Q7 in > the past and many others confirmed my impressions that modern DSP based > radios are no good when pulling call signs from the pile up of many > stations when the average level of that pileup is close to the MDS of > the radio. This is quite interesting. Forexample the old FT-1000MP is VERY poor in this respect but that radio also has some AGC issues that could contribute. 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: CW Secrets of the Masters
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In reply to this post by Bill W4ZV
Disclamer: I am a very bad CW operator,,,, :-(
But I discovered that my K2, had a rather limited low freq audio response. So I took a look at the schematic for the audio circuit in the K2... The original low freq. cutoff (-3db) freq. is approx. 640Hz (with KAF or DSP moduls installed) or 400Hz (with no audio moduls) determined by C25, C26 and the 5kOhm volume control (and NE612 mixer impedance), to extend the audio frequency response for the low freq. I put 0.1uF SMD across C25 and C26, extending the low frequency response to approx. 320Hz. This improves the SSB sound of the receiver, and improves SNR when copying low pitch CW signals. This simple mod increases the rx audio signal at 300 Hz by about 3dB. This could help those copying low pitch CW signals. just my $ .02... 73, Matti, TF3MA -- Marteinn Sverrisson TF3MA Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is 270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma Iceland _______________________________________________ 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: VP6DX -- the true story ?
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In reply to this post by Igor Sokolov-2
Igor --
Your question about DSP is an interesting one. In my limited understanding of the K3 signal path, there is always a DSP operation on the signal for filtering. While noise blanking, noise reduction, and audio effects can all be switched off, I don't know if it is possible to remove ALL digital signal processing from the signal path; i.e., operate only with the crystal filters. We certainly had plenty of marginal openings where we were required to work a pileup of signals just at the level of the underlying band/antenna noise. But... the antenna/band noise were a significant step above the receiver's underlying noise floor (10 dB)... or one turned on the pre-amp to bring the band/antenna noise above the underlying receiver noise floor. In this case, the pileup was not at the receiver's MDS level. Furthermore, the operating positions were not equipped with a second, different receiver and associated switching so that the operator could do a real-time A/B comparison between the K3 and "Brand X". Yes, signal range could be from S1 (or less) to S9+40 dB, so more than 90 dB. However, several other aspects of human hearing come into play: 1. The most sensitive part of audio spectrum for typical hearing is 2 to 5 kHz. If we take a K3 with very wide filters, and no antenna, in an extremely quiet listening environment, and just gradually advance the audio gain until we can just begin to hear the receiver noise floor, we will be listening to a higher-pitch hiss in this range of 2 to 5 kHz. White noise at lower frequencies won't be perceptible yet until the receiver gain is advanced another 10 dB (at which point frequencies down to 500 Hz are audible) or 20 dB (good for frequencies down to 250 Hz). If we narrow the receiver bandwidth so we are only listening to 100-700 Hz, for example, the receiver noise floor will appear about 10 dB louder (relative to the minimum threshold of hearing) at the higher end. 2. Another frequency-sensitive aspect of human hearing is the attenuation reflex. This reflex tightens two muscles in the ear, one of which tightens the ear drum slightly and the other moves the three bones of the middle ear to reduce the transmission to the cochlea (inner ear). This is our own, human protective AGC. The attenuation reflex begins to act at 65-70 dB above the threshold of hearing at 200 Hz... but 80 dB above the threshold of hearing at 700 Hz. The "slope" of the attenuation reflex is about -0.6; i.e., a signal that is 18 dB above the attenuation reflex threshold will be reduced to just 6 dB above that threshold (i.e., 12 dB attenuation added) by the time it reaches the inner ear. Now let's look at an operator listening to a K3 in a perfectly quiet listening environment (no other local sounds). If he adjusts the receiver so that antenna/band noise is 5 to 10 dB above his threshold of hearing at a pitch of 400 Hz, and then tunes across a CW signal that is +95 dB above the band/antenna noise floor, that CW signal will be about 100 to 105 dB above the threshold of hearing. That signal will also be about 30 dB above the threshold for triggering the attenuation reflex. At a slope of -0.6, the attenuation reflex will cut that signal down by 20 db... so that it is now 80-90 dB above the threshold of hearing. -20 dB of attenuation is about the maximum the attenuation reflex can deliver -- but that is only in children and teenagers. For adults, the maximum attenuation level declines with age, so I (at age 55) can no longer get -20 dB of protective attenuation. Maybe I get 10-15 dB of attenuation, leaving the CW signal at something like 95 dB above the threshold of hearing. Of course, once this attenuation reflex is activated, that very weak CW signal down near the noise level will be attenuated below the threshold of hearing, so no more copy. Even worse, long exposure to signals above the attenuation reflex threshold results in incremental and permanent hearing damage. So that CW signal, at 95 dB above the threshold of hearing... and 20 dB above the attenuation reflex threshold... represents an important hazard. The USA National Institute for Occupational Safety and Health has set a limit of about 1 hour per day at this level... and that limit declines quickly at higher levels. 3. Fortunately, by setting the receiver gain at these low levels, that loud CW signal is below the threshold of pain (about 110 dB above the threshold of hearing at 400 Hz). The threshold of pain is where the operator rips off the headphones and says "ouch"! We want our receivers to limit signals (or static crashes) before they reach this level! So, we can't use a receiver that is perfectly linear over a 130 dB range -- it would destroy our hearing! But we need to listen to signals in a very quiet listening environment, as quiet as we can get... and set the gain levels appropriately... and use some form of signal limiting to keep signals well below the pain threshold. And we should recognize that hearing varies from person to person. As a result, one person with poor hearing range, listening in a noisier environment and having his attenuation reflex triggered often, will have receiver AGC and his own attenuation reflex interacting to reduce signal strengths... eliminating weaker signals... while another operator listening to the same radio with good hearing (big dynamic range between his threshold of hearing and attenuation reflex trigger point), with minimal receiver AGC, will find a rich range of signals in the pileup. The psycho-acoustic phenomenon of "masking" further complicates the management of a pileup. But that's a subject for another time... -- Eric K3NA on 08 Mar 13 Thu 14:57 Igor Sokolov said the following: > Thanks Eric, > I understand you think AGC in high dynamic range radio like K3 is not > a necessity for the op with high dynamic range ears. > Actually the range should be close to 90-95 db on nowadays bands where > 59+40 signals co-exist with 1S unit signals very often. I also figured > from your post that other ops from VP6DX team choose not to use AGC > not because of some sort of problem existed in that version of the > firmware but purely because they prefer adjusting RF gain manually to > squeeze out the most from the pile up. > What about the DSP then. I experienced that myself operating from 8Q7 > in the past and many others confirmed my impressions that modern DSP > based radios are no good when pulling call signs from the pile up of > many stations when the average level of that pileup is close to the > MDS of the radio. For example we could not use Orion in the expedition > on a weak pile up on 10 and 15 meters while the same operators could > easily pick out calls using IC775. Therefore I would be happy to have > a radio where DSP could be switched on or off depending on the > situation. Did you notice the above mentioned effect while using K3? > > 73, Igor UA9CDC > > >> Privet Igor -- >> >> As best I can remember, we used MCU v1.66 and DSP 1.52. >> >> I didn't use the AGC because I did not need it. The point of >> automatic gain control is to adjust the gain of the various stages of >> the receiver in order to >> a) avoid distortion/overdriving a stage, and >> b) bring signals up/down to a comfortable listening level. >> >> (b) is not relevant to an operator who is working a pileup. (b) is >> relevant to an operator who is monitoring a frequency with one >> station transmitting. >> >> For operating a pileup, there are a variety of tools the brain uses >> to distinguish the many signals: >> -- pitch (CW) >> -- style of speaking (speech) or keying (CW) >> -- artifacts; e.g., auroral flutter, chirp, etc. >> -- strength (all). >> AGC tends to reduce the difference in signal strength, and so removed >> valuable information. >> >> In situations where static crashes interfere with reception, AGC >> hang time on a loud static crash also increases the length of time >> that a specific static crash interferes with reception. >> >> I used headphones with good audio isolation between my ears and the >> rest of the world around me. That allows me to set receiver gain >> levels with the underlying antenna/band noise just above my threshold >> of hearing... and to use at least 80 dB of my hearing range for >> listening. In this quiet listening environment, I don't need AGC. >> >> Even in a less-than-quiet listening environment, if a band is just >> open weakly (e.g., 12m to Europe), the range of signal strengths in >> the pileup can be smaller: maybe less than 30 dB between band noise >> and the strongest signal. So AGC isn't needed here either. >> >> My ideal AGC in these situations is one that only makes changes in >> receiver gain when a stage in the receiver is about to be over-driven >> (e.g., the A/D converter)... and removes those changes relatively >> quickly. Even then, it might be fine to allow the receiver to be >> over-driven (a static crash contains no information). If a signal I >> want to copy is over-driving the receiver, the best solution often is >> to reduce the RF gain manually during the duration of the time when I >> want to copy that station. If that station is just "interference" >> (e.g., a loud USA station on 80m CW calling VP6DX, when I want to >> work northern Scandinavia and northwest Russia/western Asia during >> the brief opening), I have other controls (filter bandwidth, notch) >> than might be better to use that gain reduction (automatic or manual) >> that could suppress the desired weak signals. >> >> So, almost any AGC system is inappropriate for a DXpedition or >> content environment... as long as the receiver and one's own ears >> have enough dynamic range to handle all the signals presented to it. >> The K3 has more dynamic range than other receivers. >> >> 73, >> -- Eric K3NA >> >> on 08 Mar 13 Thu 02:26 Igor Sokolov said the following: >>>> Almost all of the operators ran the K3 with AGC off (all modes). >>>> >>>> -- Eric >>> >>> Eric, can you explain what did you not like about AGC in K3? >>> Did you notice any problems with DSP being permanently on in K3 when >>> listening to heavy pile ups? >>> >>> 73, Igor UA9CDC >>> > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. 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Eric, thanks for your posting. The description of human hearing mechanics is
very educational. OK on DSP issue. Actually one other member of the dxpedition mentioned that the effect of DSP that I have described is well known to him and was present in K3 as well. He also mentioned that switching off AGC was one of the methods to overcome this effect. That was my initial reason to ask you these questions. I think you are right. DSP in K3 cannot be completely disabled (as well as in most modern DSP based radios) Therefore it is hard to tell if the effect should be attributed to DSP proper or DSP derived AGC. Anyway several people told me that they have made comparisons between DSP based radios and purely analog radios like IC781. In conditions of pile up made up of weak signals (not more then S3) analog radios always performed noticeably better. 73, Igor UA9CDC 73, Igor > Igor -- > > Your question about DSP is an interesting one. > > In my limited understanding of the K3 signal path, there is always a DSP > operation on the signal for filtering. While noise blanking, noise > reduction, and audio effects can all be switched off, I don't know if it > is possible to remove ALL digital signal processing from the signal path; > i.e., operate only with the crystal filters. > > We certainly had plenty of marginal openings where we were required to > work a pileup of signals just at the level of the underlying band/antenna > noise. But... the antenna/band noise were a significant step above the > receiver's underlying noise floor (10 dB)... or one turned on the pre-amp > to bring the band/antenna noise above the underlying receiver noise floor. > In this case, the pileup was not at the receiver's MDS level. > > Furthermore, the operating positions were not equipped with a second, > different receiver and associated switching so that the operator could do > a real-time A/B comparison between the K3 and "Brand X". > > Yes, signal range could be from S1 (or less) to S9+40 dB, so more than > 90 dB. However, several other aspects of human hearing come into play: > > 1. The most sensitive part of audio spectrum for typical hearing is 2 > to 5 kHz. If we take a K3 with very wide filters, and no antenna, in an > extremely quiet listening environment, and just gradually advance the > audio gain until we can just begin to hear the receiver noise floor, we > will be listening to a higher-pitch hiss in this range of 2 to 5 kHz. > White noise at lower frequencies won't be perceptible yet until the > receiver gain is advanced another 10 dB (at which point frequencies down > to 500 Hz are audible) or 20 dB (good for frequencies down to 250 Hz). > If we narrow the receiver bandwidth so we are only listening to 100-700 > Hz, for example, the receiver noise floor will appear about 10 dB louder > (relative to the minimum threshold of hearing) at the higher end. > > 2. Another frequency-sensitive aspect of human hearing is the > attenuation reflex. This reflex tightens two muscles in the ear, one of > which tightens the ear drum slightly and the other moves the three bones > of the middle ear to reduce the transmission to the cochlea (inner ear). > This is our own, human protective AGC. > The attenuation reflex begins to act at 65-70 dB above the threshold of > hearing at 200 Hz... but 80 dB above the threshold of hearing at 700 Hz. > The "slope" of the attenuation reflex is about -0.6; i.e., a signal that > is 18 dB above the attenuation reflex threshold will be reduced to just 6 > dB above that threshold (i.e., 12 dB attenuation added) by the time it > reaches the inner ear. > > Now let's look at an operator listening to a K3 in a perfectly quiet > listening environment (no other local sounds). If he adjusts the receiver > so that antenna/band noise is 5 to 10 dB above his threshold of hearing at > a pitch of 400 Hz, and then tunes across a CW signal that is +95 dB above > the band/antenna noise floor, that CW signal will be about 100 to 105 dB > above the threshold of hearing. > > That signal will also be about 30 dB above the threshold for triggering > the attenuation reflex. At a slope of -0.6, the attenuation reflex will > cut that signal down by 20 db... so that it is now 80-90 dB above the > threshold of hearing. -20 dB of attenuation is about the maximum the > attenuation reflex can deliver -- but that is only in children and > teenagers. For adults, the maximum attenuation level declines with age, > so I (at age 55) can no longer get -20 dB of protective attenuation. > Maybe I get 10-15 dB of attenuation, leaving the CW signal at something > like 95 dB above the threshold of hearing. Of course, once this > attenuation reflex is activated, that very weak CW signal down near the > noise level will be attenuated below the threshold of hearing, so no more > copy. > > Even worse, long exposure to signals above the attenuation reflex > threshold results in incremental and permanent hearing damage. So that CW > signal, at 95 dB above the threshold of hearing... and 20 dB above the > attenuation reflex threshold... represents an important hazard. The USA > National Institute for Occupational Safety and Health has set a limit of > about 1 hour per day at this level... and that limit declines quickly at > higher levels. > > 3. Fortunately, by setting the receiver gain at these low levels, that > loud CW signal is below the threshold of pain (about 110 dB above the > threshold of hearing at 400 Hz). The threshold of pain is where the > operator rips off the headphones and says "ouch"! We want our receivers > to limit signals (or static crashes) before they reach this level! > > So, we can't use a receiver that is perfectly linear over a 130 dB > range -- it would destroy our hearing! But we need to listen to signals > in a very quiet listening environment, as quiet as we can get... and set > the gain levels appropriately... and use some form of signal limiting to > keep signals well below the pain threshold. > > And we should recognize that hearing varies from person to person. As a > result, one person with poor hearing range, listening in a noisier > environment and having his attenuation reflex triggered often, will have > receiver AGC and his own attenuation reflex interacting to reduce signal > strengths... eliminating weaker signals... while another operator > listening to the same radio with good hearing (big dynamic range between > his threshold of hearing and attenuation reflex trigger point), with > minimal receiver AGC, will find a rich range of signals in the pileup. > > The psycho-acoustic phenomenon of "masking" further complicates the > management of a pileup. But that's a subject for another time... > > -- Eric K3NA > > on 08 Mar 13 Thu 14:57 Igor Sokolov said the following: >> Thanks Eric, >> I understand you think AGC in high dynamic range radio like K3 is not a >> necessity for the op with high dynamic range ears. >> Actually the range should be close to 90-95 db on nowadays bands where >> 59+40 signals co-exist with 1S unit signals very often. I also figured >> from your post that other ops from VP6DX team choose not to use AGC not >> because of some sort of problem existed in that version of the firmware >> but purely because they prefer adjusting RF gain manually to squeeze out >> the most from the pile up. >> What about the DSP then. I experienced that myself operating from 8Q7 in >> the past and many others confirmed my impressions that modern DSP based >> radios are no good when pulling call signs from the pile up of many >> stations when the average level of that pileup is close to the MDS of the >> radio. For example we could not use Orion in the expedition on a weak >> pile up on 10 and 15 meters while the same operators could easily pick >> out calls using IC775. Therefore I would be happy to have a radio where >> DSP could be switched on or off depending on the situation. Did you >> notice the above mentioned effect while using K3? >> >> 73, Igor UA9CDC >> >> >>> Privet Igor -- >>> >>> As best I can remember, we used MCU v1.66 and DSP 1.52. >>> >>> I didn't use the AGC because I did not need it. The point of >>> automatic gain control is to adjust the gain of the various stages of >>> the receiver in order to >>> a) avoid distortion/overdriving a stage, and >>> b) bring signals up/down to a comfortable listening level. >>> >>> (b) is not relevant to an operator who is working a pileup. (b) is >>> relevant to an operator who is monitoring a frequency with one station >>> transmitting. >>> >>> For operating a pileup, there are a variety of tools the brain uses to >>> distinguish the many signals: >>> -- pitch (CW) >>> -- style of speaking (speech) or keying (CW) >>> -- artifacts; e.g., auroral flutter, chirp, etc. >>> -- strength (all). >>> AGC tends to reduce the difference in signal strength, and so removed >>> valuable information. >>> >>> In situations where static crashes interfere with reception, AGC hang >>> time on a loud static crash also increases the length of time that a >>> specific static crash interferes with reception. >>> >>> I used headphones with good audio isolation between my ears and the >>> rest of the world around me. That allows me to set receiver gain levels >>> with the underlying antenna/band noise just above my threshold of >>> hearing... and to use at least 80 dB of my hearing range for listening. >>> In this quiet listening environment, I don't need AGC. >>> >>> Even in a less-than-quiet listening environment, if a band is just >>> open weakly (e.g., 12m to Europe), the range of signal strengths in the >>> pileup can be smaller: maybe less than 30 dB between band noise and the >>> strongest signal. So AGC isn't needed here either. >>> >>> My ideal AGC in these situations is one that only makes changes in >>> receiver gain when a stage in the receiver is about to be over-driven >>> (e.g., the A/D converter)... and removes those changes relatively >>> quickly. Even then, it might be fine to allow the receiver to be >>> over-driven (a static crash contains no information). If a signal I >>> want to copy is over-driving the receiver, the best solution often is to >>> reduce the RF gain manually during the duration of the time when I want >>> to copy that station. If that station is just "interference" (e.g., a >>> loud USA station on 80m CW calling VP6DX, when I want to work northern >>> Scandinavia and northwest Russia/western Asia during the brief opening), >>> I have other controls (filter bandwidth, notch) than might be better to >>> use that gain reduction (automatic or manual) that could suppress the >>> desired weak signals. >>> >>> So, almost any AGC system is inappropriate for a DXpedition or content >>> environment... as long as the receiver and one's own ears have enough >>> dynamic range to handle all the signals presented to it. The K3 has >>> more dynamic range than other receivers. >>> >>> 73, >>> -- Eric K3NA >>> >>> on 08 Mar 13 Thu 02:26 Igor Sokolov said the following: >>>>> Almost all of the operators ran the K3 with AGC off (all modes). >>>>> >>>>> -- Eric >>>> >>>> Eric, can you explain what did you not like about AGC in K3? >>>> Did you notice any problems with DSP being permanently on in K3 when >>>> listening to heavy pile ups? >>>> >>>> 73, Igor UA9CDC >>>> >> >> _______________________________________________ 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 Eric Scace K3NA
Eric
Absolutely fascinating and confirms many years of my own experience and suspicions. Am I right that the ear having shut down for a loud noise, takes a few ms to recover? So, a static crash doesn't just cover the signal for the period of the crash but also for a short period thereafter due to our hearing AGC. I suspect that, ideally, our headsets should be preceded with a peak limiter calibrated to the headset sensitivity to limit peak sound pressure into our ears to prevent *any* natural AGC. David G3UNA snip > Yes, signal range could be from S1 (or less) to S9+40 dB, so more than > 90 dB. However, several other aspects of human hearing come into play: > > 1. The most sensitive part of audio spectrum for typical hearing is 2 > to 5 kHz. If we take a K3 with very wide filters, and no antenna, in an > extremely quiet listening environment, and just gradually advance the > audio gain until we can just begin to hear the receiver noise floor, we > will be listening to a higher-pitch hiss in this range of 2 to 5 kHz. > White noise at lower frequencies won't be perceptible yet until the > receiver gain is advanced another 10 dB (at which point frequencies down > to 500 Hz are audible) or 20 dB (good for frequencies down to 250 Hz). > If we narrow the receiver bandwidth so we are only listening to 100-700 > Hz, for example, the receiver noise floor will appear about 10 dB louder > (relative to the minimum threshold of hearing) at the higher end. > > 2. Another frequency-sensitive aspect of human hearing is the > attenuation reflex. This reflex tightens two muscles in the ear, one of > which tightens the ear drum slightly and the other moves the three bones > of the middle ear to reduce the transmission to the cochlea (inner ear). > This is our own, human protective AGC. > The attenuation reflex begins to act at 65-70 dB above the threshold of > hearing at 200 Hz... but 80 dB above the threshold of hearing at 700 Hz. > The "slope" of the attenuation reflex is about -0.6; i.e., a signal that > is 18 dB above the attenuation reflex threshold will be reduced to just 6 > dB above that threshold (i.e., 12 dB attenuation added) by the time it > reaches the inner ear. > > Now let's look at an operator listening to a K3 in a perfectly quiet > listening environment (no other local sounds). If he adjusts the receiver > so that antenna/band noise is 5 to 10 dB above his threshold of hearing at > a pitch of 400 Hz, and then tunes across a CW signal that is +95 dB above > the band/antenna noise floor, that CW signal will be about 100 to 105 dB > above the threshold of hearing. > > That signal will also be about 30 dB above the threshold for triggering > the attenuation reflex. At a slope of -0.6, the attenuation reflex will > cut that signal down by 20 db... so that it is now 80-90 dB above the > threshold of hearing. -20 dB of attenuation is about the maximum the > attenuation reflex can deliver -- but that is only in children and > teenagers. For adults, the maximum attenuation level declines with age, > so I (at age 55) can no longer get -20 dB of protective attenuation. > Maybe I get 10-15 dB of attenuation, leaving the CW signal at something > like 95 dB above the threshold of hearing. Of course, once this > attenuation reflex is activated, that very weak CW signal down near the > noise level will be attenuated below the threshold of hearing, so no more > copy. > > Even worse, long exposure to signals above the attenuation reflex > threshold results in incremental and permanent hearing damage. So that CW > signal, at 95 dB above the threshold of hearing... and 20 dB above the > attenuation reflex threshold... represents an important hazard. The USA > National Institute for Occupational Safety and Health has set a limit of > about 1 hour per day at this level... and that limit declines quickly at > higher levels. > > 3. Fortunately, by setting the receiver gain at these low levels, that > loud CW signal is below the threshold of pain (about 110 dB above the > threshold of hearing at 400 Hz). The threshold of pain is where the > operator rips off the headphones and says "ouch"! We want our receivers > to limit signals (or static crashes) before they reach this level! > > So, we can't use a receiver that is perfectly linear over a 130 dB > range -- it would destroy our hearing! But we need to listen to signals > in a very quiet listening environment, as quiet as we can get... and set > the gain levels appropriately... and use some form of signal limiting to > keep signals well below the pain threshold. > > And we should recognize that hearing varies from person to person. As a > result, one person with poor hearing range, listening in a noisier > environment and having his attenuation reflex triggered often, will have > receiver AGC and his own attenuation reflex interacting to reduce signal > strengths... eliminating weaker signals... while another operator > listening to the same radio with good hearing (big dynamic range between > his threshold of hearing and attenuation reflex trigger point), with > minimal receiver AGC, will find a rich range of signals in the pileup. > > The psycho-acoustic phenomenon of "masking" further complicates the > management of a pileup. But that's a subject for another time... > > -- Eric K3NA > 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: VP6DX -- the true story ?
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Hi David --
Thanks for your interest in this arcane subject. When a signal just a little bit above the trigger point for the attenuation reflex appears, it takes about 150 ms before attenuation develops. For a very strong signal, the reflex is faster (25-35 ms) but there is still a period when the full power of the signal slams all the way through to the inner ear. 73, -- Eric K3NA on 08 Mar 14 Fri 06:07 David Cutter said the following: > Eric > > Absolutely fascinating and confirms many years of my own experience > and suspicions. > > Am I right that the ear having shut down for a loud noise, takes a few > ms to recover? So, a static crash doesn't just cover the signal for > the period of the crash but also for a short period thereafter due to > our hearing AGC. > > I suspect that, ideally, our headsets should be preceded with a peak > limiter calibrated to the headset sensitivity to limit peak sound > pressure into our ears to prevent *any* natural AGC. > > David > G3UNA > > snip >> Yes, signal range could be from S1 (or less) to S9+40 dB, so more >> than 90 dB. However, several other aspects of human hearing come >> into play: >> >> 1. The most sensitive part of audio spectrum for typical hearing >> is 2 to 5 kHz. If we take a K3 with very wide filters, and no >> antenna, in an extremely quiet listening environment, and just >> gradually advance the audio gain until we can just begin to hear the >> receiver noise floor, we will be listening to a higher-pitch hiss in >> this range of 2 to 5 kHz. White noise at lower frequencies won't be >> perceptible yet until the receiver gain is advanced another 10 dB (at >> which point frequencies down to 500 Hz are audible) or 20 dB (good >> for frequencies down to 250 Hz). >> If we narrow the receiver bandwidth so we are only listening to >> 100-700 Hz, for example, the receiver noise floor will appear about >> 10 dB louder (relative to the minimum threshold of hearing) at the >> higher end. >> >> 2. Another frequency-sensitive aspect of human hearing is the >> attenuation reflex. This reflex tightens two muscles in the ear, one >> of which tightens the ear drum slightly and the other moves the three >> bones of the middle ear to reduce the transmission to the cochlea >> (inner ear). This is our own, human protective AGC. >> The attenuation reflex begins to act at 65-70 dB above the >> threshold of hearing at 200 Hz... but 80 dB above the threshold of >> hearing at 700 Hz. >> The "slope" of the attenuation reflex is about -0.6; i.e., a signal >> that is 18 dB above the attenuation reflex threshold will be reduced >> to just 6 dB above that threshold (i.e., 12 dB attenuation added) by >> the time it reaches the inner ear. >> >> Now let's look at an operator listening to a K3 in a perfectly >> quiet listening environment (no other local sounds). If he adjusts >> the receiver so that antenna/band noise is 5 to 10 dB above his >> threshold of hearing at a pitch of 400 Hz, and then tunes across a CW >> signal that is +95 dB above the band/antenna noise floor, that CW >> signal will be about 100 to 105 dB above the threshold of hearing. >> >> That signal will also be about 30 dB above the threshold for >> triggering the attenuation reflex. At a slope of -0.6, the >> attenuation reflex will cut that signal down by 20 db... so that it >> is now 80-90 dB above the threshold of hearing. -20 dB of >> attenuation is about the maximum the attenuation reflex can deliver >> -- but that is only in children and teenagers. For adults, the >> maximum attenuation level declines with age, so I (at age 55) can no >> longer get -20 dB of protective attenuation. Maybe I get 10-15 dB of >> attenuation, leaving the CW signal at something like 95 dB above the >> threshold of hearing. Of course, once this attenuation reflex is >> activated, that very weak CW signal down near the noise level will be >> attenuated below the threshold of hearing, so no more copy. >> >> Even worse, long exposure to signals above the attenuation reflex >> threshold results in incremental and permanent hearing damage. So >> that CW signal, at 95 dB above the threshold of hearing... and 20 dB >> above the attenuation reflex threshold... represents an important >> hazard. The USA National Institute for Occupational Safety and >> Health has set a limit of about 1 hour per day at this level... and >> that limit declines quickly at higher levels. >> >> 3. Fortunately, by setting the receiver gain at these low levels, >> that loud CW signal is below the threshold of pain (about 110 dB >> above the threshold of hearing at 400 Hz). The threshold of pain is >> where the operator rips off the headphones and says "ouch"! We want >> our receivers to limit signals (or static crashes) before they reach >> this level! >> >> So, we can't use a receiver that is perfectly linear over a 130 dB >> range -- it would destroy our hearing! But we need to listen to >> signals in a very quiet listening environment, as quiet as we can >> get... and set the gain levels appropriately... and use some form of >> signal limiting to keep signals well below the pain threshold. >> >> And we should recognize that hearing varies from person to person. >> As a result, one person with poor hearing range, listening in a >> noisier environment and having his attenuation reflex triggered >> often, will have receiver AGC and his own attenuation reflex >> interacting to reduce signal strengths... eliminating weaker >> signals... while another operator listening to the same radio with >> good hearing (big dynamic range between his threshold of hearing and >> attenuation reflex trigger point), with minimal receiver AGC, will >> find a rich range of signals in the pileup. >> >> The psycho-acoustic phenomenon of "masking" further complicates the >> management of a pileup. But that's a subject for another time... >> >> -- Eric K3NA >> > 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 John King-10
There's also the simple fact that a given frequency separation at a lower
side tone frequency represents a greater percent difference. That is, the difference between a desired 200cps tone and an interfering 250cps tone is 25%. The difference between a desired 450cps tone and a 500cps tone is 11%. That's over a 50% difference in what the operator is asking the brain to discriminate, and that's a significant difference. ...robert At 03/13/2008 14:27, John King wrote: >400 Hz is my upper limit as well. >Lower than 300 Hz is certainly desirable to me. > >I have forty plus years on CW, and no significant >hearing loss. I do the between-the-headphones DSP >far more effectively at 400 Hz and below. > >73, > john WA1ABI > > > > -----Original Message----- > > From: [hidden email] > > [mailto:[hidden email]]On Behalf Of David Cutter > > Sent: Thursday, March 13, 2008 2:17 PM > > To: Bill W4ZV; [hidden email] > > Subject: Re: [Elecraft] CW Secrets of the Masters > > > > > > This makes perfect sense. The ears have a logarithmic response to sound > > pressure and to frequency. > > > > David > > G3UNA > > > > >> > > >> > > >> Another one that Fred K3ZO (many time winner of Dayton CW pileup > > >> contests) > > >> recently mentioned is using extremely low pitch for weak signals. Fred > > >> said many commercial ops he knew used somewhere in the 2-300 > > Hz range so > > >> he thought his favored 400 Hz was rather high! > > >> > > > 73, Bill W4ZV > > > > > _______________________________________________ > > 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 Robert G. Strickland PhD ABPH - KE2WY [hidden email] Syracuse, New York USA _______________________________________________ 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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