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Author Topic: JT65/other digital modes and noise.  (Read 1858 times)
AD0AE
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Posts: 78




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« on: January 23, 2013, 09:52:23 AM »

Hi All-

This has been something I have been wondering for a while now.  I have heard it said that JT65 and PSK31 are excellent modes to operate because they can "break through" noisy environments.  It is one of those modes you can pick up, even if your noise floor is really high.

Question: Why is that?  How does the mode work in such a way to be able to overcome (or maybe more accurately compensate) for noise?  I am curious what properties and engineering is involved that does that?  I know that with JT65 the long, slow tones have something to do with it, maybe someone could spell it out for me.

I am also wondering if there are any good documents that explain how JT65 works?  I mean to say I am curious how these long slow modes accomplish everything.  Personally, I love the mode, but I think it is black magic.  So I want to see how it works.

That being said, does anyone also have any suggestions for how to deal with people who are 'blasting' on jt65?  By that I mean people transmitting who are so loud that it actually doesn't allow you to hear weaker signals?

73s all
Steve
AD0AE
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W1VT
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Posts: 842




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« Reply #1 on: January 23, 2013, 10:47:04 AM »

http://physics.princeton.edu/pulsar/K1JT/JT65.pdf
Here is a an article written by Joe K1JT, on how it works.

The easiest way to remove strong signals is to narrow the receive bandwith, perhaps using a CW filter to only see part of the waterfall.

If you wish to work DX, I find it helps to use a vertical antenna, which has a good rejection of high angle short skip signals.

Zack W1VT
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N4UM
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Posts: 477




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« Reply #2 on: January 23, 2013, 11:01:55 AM »

JT-65 is a good weak signal/high noise mode if you don't want to have much of a conversation.  PSK31 is a very poor weak signal/high noise mode.  Olivia, MFSK and MT63 are very good weak signal/high noise modes.
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