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Author Topic: Copying in the mud  (Read 44213 times)
AD9DX
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Posts: 1467




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« Reply #15 on: September 15, 2013, 09:22:05 AM »

Also, since the DSP, EQ and ACG settings I gave Steve are K3 specific, I did not publish them here. If anyone wants them I will gladly send them to you just email me bigbadjon (at) gmail . Com

Put 82 at the end of Jon, sorry gents.
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EX, KC9TRM, KB9IRZ
K7KBN
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Posts: 2764




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« Reply #16 on: September 15, 2013, 10:12:32 AM »

I would like to work some of the weak ones also but they have to slow down. When the signal is weak and they are going blazing fast, you just cannot copy.
To make things worse, EU stations are copied on a polar path and there is a lot flutter on there signals at my qth in southern California.
I guess they are not interested in making weak signal contacts or they would slow down if they were.

The only thing that's going to improve your copying ability at fast speeds under poor conditions is PRACTICE.  Whether they slow down doesn't matter.  Get the practice copying fluttery polar signals buried under a few other signals.  My hearing has degraded quite a bit from when I was in the Navy copying code, but I can still pull weak ones with lousy fists out and copy what they have to say.  And it's because I practiced then, and I still do.
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73
Pat K7KBN
CWO4 USNR Ret.
WX2S
Member

Posts: 685




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« Reply #17 on: September 15, 2013, 07:30:11 PM »

I don't have one on my K3 yet. I typically just hit the REV button then use the main VFO knob to figure out where the other side of the QSO is, then spin just above that guy and wait my turn. There are a lot of different strategies figuring out the pattern of a DX station. For me, I would much rather have a Pan Adapter than a sub reciever although given enough time, I will have both  Cheesy
I've got to admit, with the P3 and the SVGA display, the sub receiver is not all that necessary in pileups. With that said, the practice can be deceiving. Some stations will think the DX is calling them and respond. Some stations will continue to call no matter what. It all looks the same on the pan adapter.
« Last Edit: September 15, 2013, 07:32:16 PM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
NO2A
Member

Posts: 758




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« Reply #18 on: September 15, 2013, 11:05:12 PM »

Want to copy in the mud? Put up a low dipole on 80m and have fun! Was on that band earlier tonight and worked 2 dx stations,and a guy running an HW-8 in Ohio! All in very noisy qrn conditions,using the dsp to hear them. My best was the UT7,which took a few tries with QRO. The noise was horrible. It`s truly amazing what you can work if you listen. Some of my most satisfying qso`s have been with qrp stations on 80m cw. Don`t forget to use the r.i.t. cause often the qrp may be off frequency,or below your frequency. It does make one a better operator. Sometimes i.f. shift can work well on older radios without dsp.
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AD9DX
Member

Posts: 1467




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« Reply #19 on: September 16, 2013, 04:37:53 AM »

I don't have one on my K3 yet. I typically just hit the REV button then use the main VFO knob to figure out where the other side of the QSO is, then spin just above that guy and wait my turn. There are a lot of different strategies figuring out the pattern of a DX station. For me, I would much rather have a Pan Adapter than a sub reciever although given enough time, I will have both  Cheesy
I've got to admit, with the P3 and the SVGA display, the sub receiver is not all that necessary in pileups. With that said, the practice can be deceiving. Some stations will think the DX is calling them and respond. Some stations will continue to call no matter what. It all looks the same on the pan adapter.


You have to be fast, and you have to be able to figure out the rhythm. It's not a perfect system, but it does help. Without being in the DX station's shack there is no perfect way to figure out where you should transmit. 
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EX, KC9TRM, KB9IRZ
N3HEE
Member

Posts: 113




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« Reply #20 on: September 16, 2013, 05:46:02 AM »

Let's not forget about using a good RX antenna to improve signal to noise ratios.  I use a Hi-Z three element phased vertical array with 50 foot spacing in my small backyard.  It makes the difference between hearing or not hearing some weak signals !   I have that antenna connected to my K3.  I sent email to Jon for his K3 settings.  I shared some of mine with him.  Nothing out of the ordinary but I found a way to greatly reduce static crashes by setting my CW RX EQ to cut every band by 16DB except 400 HZ.  I'm sure other radios have a RX EQ that can be adjusted accordingly. 

I would also agree that an experienced pair of ears plays a BIG roll in coping cw signals at or below the noise floor.

Good thread !

Joe
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WA9FZB
Member

Posts: 171




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« Reply #21 on: September 18, 2013, 02:33:39 PM »

For some of the really weak ones, I sometimes use an outboard active audio filter that "peaks" a specific narrow audio bandpass.  This acts much like the old-timers' Q-Multipliers in that it will bring one single tone up out of the mud.  If the bandwidth is too narrow, it can cause ringing, but when set just below that point it works to keep one signal front-and-center.  The filter I use most is an old MFJ unit (forgot the model number) but I also have an old homebrew filter as well.
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AD9DX
Member

Posts: 1467




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« Reply #22 on: September 19, 2013, 04:44:41 AM »

For some of the really weak ones, I sometimes use an outboard active audio filter that "peaks" a specific narrow audio bandpass.  This acts much like the old-timers' Q-Multipliers in that it will bring one single tone up out of the mud.  If the bandwidth is too narrow, it can cause ringing, but when set just below that point it works to keep one signal front-and-center.  The filter I use most is an old MFJ unit (forgot the model number) but I also have an old homebrew filter as well.

I use one of those SCAF filters for that very same reason. It doesn't always work, but the incidents where it does, it makes a world of difference.
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EX, KC9TRM, KB9IRZ
NI0C
Member

Posts: 2383




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« Reply #23 on: September 19, 2013, 07:54:00 AM »

For some of the really weak ones, I sometimes use an outboard active audio filter that "peaks" a specific narrow audio bandpass.  This acts much like the old-timers' Q-Multipliers in that it will bring one single tone up out of the mud.  If the bandwidth is too narrow, it can cause ringing, but when set just below that point it works to keep one signal front-and-center.  The filter I use most is an old MFJ unit (forgot the model number) but I also have an old homebrew filter as well.

I use one of those SCAF filters for that very same reason. It doesn't always work, but the incidents where it does, it makes a world of difference.
The APF (Audio Peak Filter) in the K3 works wonders sometimes, too.
73,
Chuck  NI0C
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N3HEE
Member

Posts: 113




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« Reply #24 on: September 19, 2013, 12:49:14 PM »

For some of the really weak ones, I sometimes use an outboard active audio filter that "peaks" a specific narrow audio bandpass.  This acts much like the old-timers' Q-Multipliers in that it will bring one single tone up out of the mud.  If the bandwidth is too narrow, it can cause ringing, but when set just below that point it works to keep one signal front-and-center.  The filter I use most is an old MFJ unit (forgot the model number) but I also have an old homebrew filter as well.

I use one of those SCAF filters for that very same reason. It doesn't always work, but the incidents where it does, it makes a world of difference.
The APF (Audio Peak Filter) in the K3 works wonders sometimes, too.
73,
Chuck  NI0C

Chuck, I find the APF in my K3 to be pretty limited on weak signals.  I cant seem to get weaker signals to pop out of the mud.  If the signal is a little stronger then I can.  Perhaps you can expand on how you are using it.  Thanks -Joe
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NI0C
Member

Posts: 2383




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« Reply #25 on: September 19, 2013, 04:54:37 PM »

KB3KJS wrote:
Quote
Chuck, I find the APF in my K3 to be pretty limited on weak signals.  I cant seem to get weaker signals to pop out of the mud.  If the signal is a little stronger then I can.  Perhaps you can expand on how you are using it.  Thanks -Joe
Joe, make sure you use FINE (1 Hz display resolution) for the main tuning, and use the shift control, too.  The Macro's listed here might be useful in setting up your APF: http://www.ke7x.com/home/k3-macro-repository

73,
Chuck  NI0C
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AG1LE
Member

Posts: 117


WWW

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« Reply #26 on: September 19, 2013, 07:39:23 PM »

I'd like to improve my ability to copy CW signals that are close to the noise floor. This would be useful for QRP, DX, or just general hamming. Can some of the wise folks here give me any practical advice?

Rob Frohne KL7NA has software that allows creating CW signals (.WAV files) close to noise floor. I have used Rob's software to create test audio files - see  http://ag1le.blogspot.com/2012/04/experiment-decoding-multiple-morse-code.html.  When working on FLDIGI CW decoder software I used these files for testing - see http://ag1le.blogspot.com/2012/05/fldigi-adding-matched-filter-feature-to.html.

Copying CW signals at -5 ..-15 dB SNR levels requires a lot of focus and attention. I did also some testing how SNR impacts decoding error rate - see http://ag1le.blogspot.com/2013/01/morse-decoder-snr-vs-cer-testing.html.  I would be interested in getting some human performance data if you are able to check your results at different SNR levels.

73
Mauri AG1LE
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WX7G
Member

Posts: 5920




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« Reply #27 on: September 21, 2013, 06:03:34 AM »

Mauri,

in your SNR experiment you specify the SNR in a 3 kHz bandwidth, correct? When you add a bandpass filter are you still specifying the SNR in 3 kHz or in the new filter bandwidth?

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AG1LE
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Posts: 117


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« Reply #28 on: September 22, 2013, 04:25:40 AM »

Mauri,

in your SNR experiment you specify the SNR in a 3 kHz bandwidth, correct? When you add a bandpass filter are you still specifying the SNR in 3 kHz or in the new filter bandwidth?

Correct. In the CER/SNR experiment referred above I injected noise with Pathsim using 3 kHz bandwidth. To keep results comparable between different tests (decoding algorithms, matched filter / FFT filter) I used the SNR in the 3 kHz bandwidth. 

As you can see from the results optimizing filter bandwidth to CW bandwidth (speed dependent) has a significant positive impact on the error rate as expected.

Human auditory system seems to be able to perform pretty amazing filtering itself, though using narrow bandpass filter appears to improve decoding accuracy for humans as well. I have found some research done in 1970s on this topic.  In most papers they refer to SNR in the original audio bandwidth.

73
Mauri AG1LE


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WX7G
Member

Posts: 5920




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« Reply #29 on: September 22, 2013, 05:36:09 AM »

Thanks. So the test shown below having a CER of 0.00999 at -10 dB SNR in 3 kHz is actually a +9 dB SNR in 35 Hz.

-10 dB         0.00999   SOM Decoder with FFT Filter @35 Hz
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