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Author Topic: What kind of CW signal would 5 db out of noise be  (Read 4344 times)
VK5EEE
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« Reply #15 on: July 10, 2017, 06:53:04 PM »

 Cheesy Wow that's great work OM Wim! That signal sounded RST 559 to me, absolute QRK5. I'd love to hear some 1dB if you can make that for us, or on the limits of ability to decipher in noise, wondering what level I can filter with my ears? According to https://en.wikipedia.org/wiki/Minimum_detectable_signal#Signal-to-noise-ratio it is 1dB. I thought I can hear CW BELOW noise level though? From http://www.pa3fwm.nl/technotes/tn09b.html I see -12dB for 12WPM can (also) you produce a file at -12dB 24WPM for a test?
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
PA0WV
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« Reply #16 on: July 11, 2017, 03:52:16 AM »

Chuck es Lou
same place -10 dB SNR 24 wpm 712 Hz bandlimited flat noise 300-2400 Hz

http://pa0wv.home.xs4all.nl/K1LEM/MINUS10.WAV

cu 30
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NI0C
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« Reply #17 on: July 11, 2017, 05:54:01 AM »

Wim,
Thanks for the file.  I will have to admit it is not solid copy for me-- the easiest parts were my call sign twice and yours near the beginning and end of the file, and the numbers for the band edges of the audio.  I went back to listen to one of the files from AG1LE at -10 dB. and found his a bit easier to copy, probably because of the lower pitch code, and perhaps also the band limits of his noise source versus yours.  Nice work, and fun stuff to study and practice for sure.  I'll bet Lou did better than me.
73 de Chuck  NI0C 
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VK5EEE
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« Reply #18 on: July 11, 2017, 06:43:32 AM »

Well very interesting! Thanks Wim for the great test, now we know what -10dB is like. Like NI0C said maybe if the pitch is lower AND speed slower, things will no doubt greatly improve. I don't think my half hearing level has any detrimental effect, as I raised the volume and listened with ear buds. First time I got maybe half of it, then another few listens and I could slowly complete more of it, but not all:

VK5EEE VK5EEE = NI0C NI0C DE PA0WV PA0WV THIS IS 512 HZ MORSE CODE 24 WPMWITH A LEVEL OF 5EL....LAVIK DB S/N RATIO IN FR..T...ES BANDLE..ZEED KEY AT 200 AND 2800 HZ 73 CUAGN 30 DE PA0WV PA0WV CL

Not solid copy, some guessing based on timing and letters.

Pray tell, was it 512Hz? Thought pitch sounded higher than that. WPMWITH was joined together:-) but can't make sense even after listening several times to a few other parts, what did you send? Checking what you wrote earlier, looks like I got 512 instead of 712 and 200 instead of 300? But some mysterious parts, what were those!

So I guess we can conclude copying CW down to about -10dB S/N (2 S points below noise? Seems about right!) is our limit, and then it needs to be a bit slower so the dits and dahs are longer, probably we could get most or all of it at 12 WPM.

Maybe instead of filling us in, if it's not too much trouble, produce it again with same pitch and S/N but at half the speed? That'd be interesting to see how much the QRK goes up!

I'd say QRK2/3 at best, QRK2 overall.
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
VK5EEE
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« Reply #19 on: July 11, 2017, 06:47:57 AM »

That one, I'd have given an on air RST 229!
I only give S1 if I can truly BARELY PERCEIVE it, and inevitably an R of 1 with it Smiley I never go by S meter as I think the S descriptions are not intended for use with S meters.
Interesting how at low noise levels RST usually seems to work as 119, 229, 339, 449, 559, for me on 20m anyway, though on e.g. 10m 539 is common, and on 80m, at least for me, 359 is common.
I'm convinced though that some give S from the S meter with Attenuator and Notch on, and Pre-Amp off :-)
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
VK5EEE
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« Reply #20 on: July 11, 2017, 08:27:19 AM »

Maybe someone else can have a listen and fill in the blanks first before all is revealed?
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
GW3OQK
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« Reply #21 on: July 11, 2017, 08:36:19 AM »

Wim, that file at 5 db s/n ratio is easy to copy. The file at -10 db is unintelligible to me. I can write down odd letters and get the repeated callsigns so I would give it rst 119. Well done Lou, you must have good audio filters in your ears. Yes it would be interesting to hear -5 an 0 db s/n, before all is revealed!
73
Andrew
In a contest you would give 599 of course.
« Last Edit: July 11, 2017, 08:38:32 AM by GW3OQK » Logged
PA0WV
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« Reply #22 on: July 11, 2017, 01:15:41 PM »

Congrats Lou that you could copy that. Very good. Compare with G3OQK, who I thank for rprt. Real selective hearing. I tell you more about that later. You asked for  1 dB SNR but I knew that should not be a problem at all so I selected -10 dB. Not -12 dB that seems to me too low.

I am busy however - and 80+ aged, it is all going extremely slowly, fast tired and so on - with an article in Dutch language cuz my English is too bad (even less than classic Latin and Greek) for CQ-QSO (a Belgian bimonthly, French and Dutch language) It will also published afterwards on my website, when still alive. Compares Nato alphabet SSB - nato compressed SSB, and Morse code 12 wpm.

Today I drove 300 km because molar 26 was broken, about half off on the inside tongue side, it could be repaired with  some composite, so slowly my body is changing in plastic.

Did me think on the guy that lost a leg in an traffic accident, and he purchased  a grave where the separated leg was buried, and when he died the rest of his body will be added added, for completion. So he is a real example of the Dutch proverb"Staying with one leg in your grave".

Hay: I am rag chewing on a forum, I  ought to do that in the ether.

cu 73=30
« Last Edit: July 11, 2017, 01:22:36 PM by PA0WV » Logged

PA0WV
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« Reply #23 on: July 11, 2017, 01:45:55 PM »

Wim,
Thanks for the file.  I will have to admit it is not solid copy for me-- the easiest parts were my call sign twice and yours near the beginning and end of the file, and the numbers for the band edges of the audio.  I went back to listen to one of the files from AG1LE at -10 dB. and found his a bit easier to copy, probably because of the lower pitch code, and perhaps also the band limits of his noise source versus yours.  Nice work, and fun stuff to study and practice for sure.  I'll bet Lou did better than me.
73 de Chuck  NI0C 

Chuck, the band limited flat spectrum noise  300-2800 Hz is produced with a 1025 long FIR filter. With the public domain program Audacity you can look at the spectrum with the  build in FFT and it looks like  really perfect.

May be the lower pitch is of advantage, I found many years ago and could not find it back,  a publication from ARRL labs that the estimated bandwith of the brain for detecting CW was one octave, so a lower pitch must be better.
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VK5EEE
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« Reply #24 on: July 11, 2017, 04:02:09 PM »

LOL @ 599 in a contest, indeed!

Wim, sorry to hear about your tooth and 300km drive!!! Yes, you must rest as  much as is possible, and don't feel obligated or stressed to do anything here. It was great of you to spend so much time on this, not only because of being tired, but also, the older we get, the less time we have left, the more valuable it is. Oddly the older we get the more patient we get, when it should be the other way around since time is more precious!

If you do have something published later on in Dutch, just send us the URL and we can use Google Translate to read it?

I wonder what those mysterious parts that I could not get from under the noise were was impressed as I thought others may do better. I guess it is training over the many years? I did listen to an awful lot of weak signals in the noise. I have tinnitus, but that doesn't seem to get in the way, the pitch is much much higher, though unfortunately the volume too. Perhaps filtering that out in the brain, helps the training!

But, the flip side is, that sometimes I actually THINK I hear CW when none is there, maybe just imagination or some other noise. I don't usually make sense of it, but an overactive imagination can lead me to thinking I heard a response to a CQ when perhaps there was nothing.

I'd love to hear from you later on more about selective hearing if you ever get Zeit und Lust (time and desire) as they say in German.

Well now we know we can more or less read -10dB S/N Morse though no doubt half the speed would make that a QRK3 or 4. This is also proof that some modern digital modes are more effective at very low S/N ratios, and I experienced that with Pactor where I could not even hear the signal!
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
W9OY
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« Reply #25 on: July 11, 2017, 07:59:22 PM »

With a signal close to the noise or even under the noise it's important to properly adjust the AGC so you radio has maximum gain and is not into gain compression.  On 160 I often just turn the AGC off.

73  W9OY
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K0UA
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« Reply #26 on: July 11, 2017, 08:31:28 PM »

The +5db above the noise... No problem, I could copy that.   The -10db.. I could tell there was a signal there.  I couldn't copy a single letter for sure, and certainly no words.   -10db would be a pretty good signal for jt65 or jt9, it would be 100 percent copy, of course the thru put is very slow..  Obviously there are huge differences in human ears and the ability to dig out weak signals.  My filters and codecs are just not very good.  While I didn't try it, maybe some decoders could copy the +5, but I have never seen anything in a pc that could copy the -10 or even know it was there.
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GW3OQK
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« Reply #27 on: July 12, 2017, 03:27:08 AM »

Instead of the small computer headset half off my ears I plugged in my padded radio headphones and adjusted the computer volume control to a proper quiet level. That made a useful difference. I definitely needed to "copy behind" but still can't copy like Lou.

I got .... VK5EEE = O0C .. C DE PA0WV PA0WV THEN IS C12 SEG MORSE CODE JV WPM MENTH LEVEL OF DED A MLTWEK ... DO NO CN RATIO ... 100 .... PA3WV PA3WV RR

I have always prided myself on copying weak signals, or separating signals of different tones in a wide bandwidth with my tunable hearing. With a real radio and a bandwidth of 500 Hz I sometimes seem to hear morse like Lou.

Here's an example of a weak signal. It is Don VE3LYX in Canada using his 1 watt WW2 Wireless Set 19 on 7 MHz, as received in UK.  www.v-d-r.net/images/VE3LYX 130916.mp3 It is clearly above noise but by only a dB I guess.
73
Andrew
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NI0C
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« Reply #28 on: July 12, 2017, 05:29:17 AM »

A previous discussion on attempts to measure the limits of copying weak signal Morse is found here: http://www.eham.net/ehamforum/smf/index.php/topic,92347.15.html
73, Chuck  NI0C
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VK5EEE
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« Reply #29 on: July 12, 2017, 06:45:24 AM »

Andrew, I was looking at your QRZ page, all I can say is WOW not only to the lovely old gear but your home brewing. I'm unfortunately not one of those who understands and can build radio gear I wish I was, I envy those like yourself who can. I just crammed the technical stuff for the exam, understanding enough of it to get through (at the time, fortunately it's not a yearly test or I'd now fail!) obviously CW was a cinch, and radio regulations too. But I do wish I could make the type of gear you do, my HOPE is that in future years I may get to it. I started with assembling a Pixie :-)!

I had a lot of trouble to copy VE3LYX I could only clearly hear the LYX, I would not have got that it was VE3LYX from that sample. Love the QRH though!

Chuck, unfortunately those files are no longer online, I was searching for them earlier, also from those forum posts, he must have deleted them by now.
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Long Live Real Human CW and wishing you many happy CW QSO - 77 - CW Forever

Support CW and join CW clubs. QTT: FIST#1124, HSC#1437, UFT#728, RCWC#982, SKCC#15007, CWOPS#1714, 30CW#1,
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