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1-10 of 19 messages
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PSK31 vs CW...
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by KA3DNR on October 7, 2009
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Hello Folks,
I have read somewhere that PSK31 is much more "efficient" than CW. Have any of you made some empirical comparisons to test this out? In my light-work comparison, the weakest signal I hear on PSK31, I could also work on CW. But, what do I know?
Your thoughts? Do you have any juicy PSK31 sites explaining its superiority?
Regards & Thanks,
Marc
KA3DNR
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RE: PSK31 vs CW...
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by W4KVW on October 7, 2009
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I think the PSK signal is EASIER for WEAK signals but I am NOT an EXPERT just from my limited use of both modes.
Clayton
W4KVW
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RE: PSK31 vs CW...
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by K7JBQ on October 7, 2009
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I use both CW and PSK on a regular basis.
For really weak signal work, CW wins, assuming the processor between the ears is up to snuff.
Stuff I can hear well enough to work on CW, often times results in garbled print on PSK.
73,
Bill
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RE: PSK31 vs CW...
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by N3OX on October 7, 2009
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"Stuff I can hear well enough to work on CW, often times results in garbled print on PSK. "
That's also my experience.
My quick Googling suggests that people argue a couple of things:
1) Phase shift keying is better than amplitude shift keying.
2) The bandwidth appropriate for of a CW signal is the width of commonly used CW filters so that the bandwidth of a CW signal is perhaps 10-15 times greater than that of a PSK31 signal. The increased power spectral density gives a similar boost going from CW to PSK as you get from going from SSB to CW.
I think #1 is absolutely true for computer decoding. Amplitude shift digital modes are very hard to decode in the presence of noise and interference by comparison. It's hard to tell "on" and "off" by amplitude when one second's "on" state is 15dB louder than the last second's "on" state.
#2 isn't really true and I can't make a very rigorous argument at this late hour, but I think there are a lot of people using telecommunications theory without really stating their assumptions well.
It's certainly not the case that a CW signal is spread evenly over a 500Hz or 300Hz filter bandwidth. Far from it.
Both 1 and 2 fall to an additional problem. On the "receiving" end... and by that I mean after the radio has done its thing, the CW signals are further processed by an amazing, adaptive, predictive pattern recognizing filter and decoding software.
In the "hardware" of that filter you've got ears and a brain that are able to focus in a trainable way on a narrow segment of received audio. You can have a few CW signals in your passband and choose to listen to each one and ignore the others. You can choose to listen to narrow your filter bandwidth down to listen to the coherent switched tones and not the noise. It's not clear to me how to take that into account in this argument.
And in the "software" end, we can PREDICT that soon there's very important information coming after "RST is" and we're primed and ready to receive that very difficult to hear "349 349 349" from JA7xxx on 160m.
We know that after "CQ CQ DE" comes some other very important information.
Wouldn't it be nice if you could tell your PSK software to LISTEN HARDER at the right time so your screen didn't look like:
CQ CQ DX CQ DX de V#(gA8FA F(30A
CQ CQ DX C) DX de V8#@) * F)*#@$
CQ CQ DX CQ DX de #$)_0 )*V 3281
PSE K K
?
We don't have to be content with what we actually hear. We can take what we actually hear and ask ourselves if it was probably true, and look for some sense in it. We're not going to EVER decode punctuation in a callsign, for example.
Even if it sounds like it, you're not going to decode
CQ de W7?
You're going to figure out it was
CQ de W7UTI
or
CQ de W7IMI
Furthermore, the ear-brain filter knows the difference between signal and noise. This is something of an interesting concept. As good pattern recognizers, we just intuitively know signal from noise. We have a complex set of rules that we apply at blazing speed to tell the difference, and we have the disadvantage that we don't know exactly how it works, so we can't tell our computers how to do it. We're SO good at it that when we get started in radio we might think "why can't a manufacturer make a radio that just gets rid of the noise?!"
Anyway, I think PSK31 is a good weak signal mode. But asking if it's better than CW may not even be a well formed question, given the nature of the CW decoder.
And I think there may be some other technical issues (related only to engineering questions, not deep into the neuroscience) that people get a little wrong when they estimate how good PSK31 is vs. CW.
73
Dan
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RE: PSK31 vs CW...
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by KA3DNR on October 8, 2009
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Excellent Dan!
Thank you, and others, for taking the time to respond.
What you had stated is down the same train of thought I was going through.
Regards,
Marc
KA3DNR
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RE: PSK31 vs CW...
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by AA4PB on October 8, 2009
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I don't know, but under certain conditions I've copied some PSK31 signals that I couldn't even hear so I seriously doubt that I could have copied them on CW. Of course using the appropriate IF filter and headphones I might have been able to dig them out of the noise.
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RE: PSK31 vs CW...
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by 5R8GQ on October 8, 2009
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Guess it depends on what you mean by "efficient".
The Free Dictionary.com: Efficient
a. Acting or producing effectively with a minimum of waste, expense, or unnecessary effort.
b. Exhibiting a high ratio of output to input.
Minimum of expense and electrical energy:
QRP CW rig, lantern battery and simple wire antenna.
Minimum of unnecessary effort:
Point and click on a PSK signal and start typing.
QRP PSK works really well too.
You can make a good argument for each mode.
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RE: PSK31 vs CW...
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by G0GQK on October 8, 2009
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It has been said that PSK31 is comparable to Morse code because of the narrow signal but I don't think there is an advantage. However if Morse transmissions are compared to modes like WSPR where data can be received when a signal cannot be seen or heard, then WSPR will be the better mode.
G0GQK
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RE: PSK31 vs CW...
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by KA3DNR on October 8, 2009
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Hello Mel,
I didn't know WSPR existed; I am intrigued.
Usage is going up in a linear fashion:
http://wsprnet.org/drupal/wsprnet/stats
I need to learn more about this. It appears to be beacon-like communication, not a QSO per se. I am ignorant. I'll go to the forums and start asking questions.
Thanks again Mel!
Regards,
Marc
KA3DNR
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RE: PSK31 vs CW...
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by K5MBV on October 15, 2009
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Marc, you might be better investigating the WSJT modes
that can yield good copy on signals that can not
be heard at all. FSK441 and JT65B for example. One
for meteor scatter and the other for EME. They are
actual communication programs quite a bit different
from WSPR and can copy signals 20dB or so weaker than
CW can.
Ken K5MBV
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