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Author Topic: What is the best speed for weak signal contacts  (Read 2177 times)
KH2BR
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Posts: 101




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« on: September 21, 2012, 11:27:21 PM »

I guess the subject line speaks for its self but I just wonder what speed is best for making a weak signal contact?
Some weak signals just cannot be copied because they are going to fast. I can copy up to 30wpm but a weak signal with qsb near the noise level just cant be copied.
I think if they slow down that could be better.
What say  Huh?  I am thinking qrp stations calling me while I am running 100 watts. I did make a local contact at 100 miliwatts on a qrp rig, and I was doing about 10 wpm and that worked.

Bob  KH2BR
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PA0BLAH
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Posts: 0




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« Reply #1 on: September 22, 2012, 09:33:55 AM »

Yeah Bob you got no answer, I conclude.

That is because your question does not exist.

When you have noise, the average is zero. When you add a constant signal, the average grows with time. So when you make dots of one hour en dashes of 3 hours you can integrate the signal and find out that deep in the noise there was a dash or a dot. So time is exchangeable with signal to noise ratio.

Not satisfied?
Straight answer, to copy in your head weak signals, take 5 to 10 wpm. Ham experience over 65 years.  Must do, huh?

Bob
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SV1XV
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Posts: 93


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« Reply #2 on: September 22, 2012, 10:45:46 AM »

When you have noise, the average is zero. When you add a constant signal, the average grows with time. So when you make dots of one hour en dashes of 3 hours you can integrate the signal and find out that deep in the noise there was a dash or a dot. So time is exchangeable with signal to noise ratio.
Correct. This is the idea behind QRSS, used by hams and HiFERs for very low power beacons or for beacons operating on 136 kHz.

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W8JI
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« Reply #3 on: September 30, 2012, 04:50:40 PM »

If you ask 160 meter operators with many years of experience, a modest speed of about 15 WPM is best for operator copy. Much faster is difficult to copy in noise, much slower is more difficult also.

A good weak signal CW operator can copy many dB below noise power if speed is modest.

30 WPM is far too fast, as any 160 DX operator knows. Everyone experienced hates weak signals who insist on 30-40 WPM.

Going much slower than 15 WPM is worse also, because the rhythm is very difficult to sort.

This is for experienced humans, not machines.
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PA0WV
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Posts: 98




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« Reply #4 on: September 30, 2012, 05:20:37 PM »

If you ask 160 meter operators with many years of experience, a modest speed of about 15 WPM is best for operator copy. Much faster is difficult to copy in noise, much slower is more difficult also.


Going much slower than 15 WPM is worse also, because the rhythm is very difficult to sort.

This is for experienced humans, not machines.

As a matter of fact I constructed with a program written in a general purpose programmimg language white noise (random numbers) and a sign wave 600 Hz, for different speeds starting at 5 wpm and signal to noise ratios, for me it turned out that with plain Dutch language random chosen words 6 characters long, the optimum for head copy was flat between  5 and 10 wpm. Just the correct copied words were maximum in number for the lowest S/(S+N) ratio in that speed range. 15 wpm was less  and higher, deteriorates fast (needs less noise to copy reliable)

Some results (wav files) can still be found on my website http://pa0wv.home.xs4all.nl/zelfbouw.html

Of course it requires without noise more concentration to copy 5 wpm then 15 wpm without, but still that was my result.

I remember DJ1YFK did also this kind of tests, as I read some time ago on his website.
« Last Edit: September 30, 2012, 05:27:20 PM by PA0WV » Logged
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