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eHam Forums => CW => Topic started by: WX2S on September 13, 2013, 07:21:00 PM



Title: Copying in the mud
Post by: WX2S on September 13, 2013, 07:21:00 PM
Hi, all,

Not sure where to post this, so I'll try here.

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?

Thanks and 73, - Steve WX2S.


Title: RE: Copying in the mud
Post by: KB4QAA on September 13, 2013, 07:28:59 PM
Experience, experience, experience.  Proper use of filters and radio settings.

I don't know what kind of radio you use, but the more modern it is the more gadgets there are that get between you and the signal, e.g. DSP, NR, NB, Passband/IF Shift, AGC (should be OFF or Fast), Notch Filter/ANF, AF/IF Filters, RF Gain

When copy gets tough, turn everything off and add the gadgets back in one at a time.

Sooo, Experience in code copy, and experience in gadget use are the keys.


Title: RE: Copying in the mud
Post by: NI0C on September 13, 2013, 07:35:42 PM
Try the pileup simulation program, Pileup Runner, available free at: http://www.dxatlas.com/pileuprunner/

Of course, it emphasizes QRM, but you can look at the waterfall display to find weak signals.
73,
Chuck  NI0C


Title: RE: Copying in the mud
Post by: KH6AQ on September 13, 2013, 08:03:24 PM
None of the CW simulator programs I know of simulate a signal at or below the noise floor. Some suggestions for obtaining such practice:

1. Tune around for suitable signals
2. Inject RF noise into the antenna (I can post the schematic of a wideband RF noise generator if someone can tell me how to post a pic here)
3. Play a recording of a noisy frequency with no signal into the headphones along with a simulated or off-the-air CW signal


Title: RE: Copying in the mud
Post by: NI0C on September 13, 2013, 08:25:02 PM
None of the CW simulator programs I know of simulate a signal at or below the noise floor.
Pileup Runner does produce such signals.  Just to check this out, I just "worked" a station with a rated strength of 0 dB.  (After logging the "QSO," the program indicates the signal strength of the station).   


Title: RE: Copying in the mud
Post by: KH6AQ on September 14, 2013, 03:04:18 AM
NI0C,

thanks for telling us about Pileup Runner. I tried it and it's pretty good but the version I downloaded would not allow the average S/N ratio to be set lower than 3 dB and it does only pileups. A useful modification of this program would be single station QSOs with S/N ratio settable to -10 dB.

I'll be practicing with Pile Runner this weekend.



Title: RE: Copying in the mud
Post by: M0LEP on September 14, 2013, 05:06:20 AM
I think G4FON has some signal twiddling options which might simulate poor signals...


Title: RE: Copying in the mud
Post by: W1JKA on September 14, 2013, 05:42:42 AM
  Playing in the QRP cw mud hole is my favorite part of the hobby since I'm into qrp/dx.Via three years of trial/error/experimenting I have ended up using my home based K-1 with a cheap Hi-Permite  outboard audio filter. With this combo I can seperate/pick out and work weak noise level qrp stations by simply using the narrow F3 K-1 filter to seperate and then fine tuning the cw pitch on the Hipermite to a level I can distinguish the note from other louder on freq. or close by stations. I also use these hipermites with my MFJ Cubs to accomplish the same.


Title: RE: Copying in the mud
Post by: K8AXW on September 14, 2013, 07:51:39 AM
Steve, if ya wanna play in the mud, you're just gonna have ta get down in the mud with them!

Be prepared to get "dirty", get headaches, have losses and some discouragement.  But when you shut off the radio you'll look like the glassy-eyed, grinning little boy who has just had a wonderful session with a mud puddle!


Title: RE: Copying in the mud
Post by: AD9DX on September 14, 2013, 12:17:26 PM
Steve check your facebook private message box, I know we have the same rig, so I sent you a few "tips" on ways to declutter the mud pit.  But as said above, your are not trying if you don't have a bottle of aspirin next to your headphones. 


Title: RE: Copying in the mud
Post by: N3QE on September 14, 2013, 12:38:08 PM
With weak signals, I always make sure AGC is off.

If it's lightning crash type noise, having a lightning crash reduce the gain through AGC (until AGC time constant increases it again) is the worst.

Rarely will I turn the gain up so much that band noise is loud. That's just too much gain and counter-productive for picking out the signal.


Title: RE: Copying in the mud
Post by: WX2S on September 15, 2013, 04:07:37 AM
Thanks to everyone for their help. I've put AD9DX's settings suggestions into practice and they do seem to make a difference.

What are all of y'all's thoughts on using the sub in pileups? Is it more important to hear the pileup or to get the DX in both ears?

73, -WX2S.


Title: RE: Copying in the mud
Post by: AD9DX on September 15, 2013, 05:59:37 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  :D


Title: RE: Copying in the mud
Post by: AD9DX on September 15, 2013, 06:01:18 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


Title: RE: Copying in the mud
Post by: KH2BR on September 15, 2013, 08:10:01 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.


Title: RE: Copying in the mud
Post by: AD9DX 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.


Title: RE: Copying in the mud
Post by: K7KBN 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.


Title: RE: Copying in the mud
Post by: WX2S 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  :D
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.


Title: RE: Copying in the mud
Post by: NO2A 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.


Title: RE: Copying in the mud
Post by: AD9DX 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  :D
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. 


Title: RE: Copying in the mud
Post by: N3HEE 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


Title: RE: Copying in the mud
Post by: WA9FZB 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.


Title: RE: Copying in the mud
Post by: AD9DX 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.


Title: RE: Copying in the mud
Post by: NI0C 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


Title: RE: Copying in the mud
Post by: N3HEE 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


Title: RE: Copying in the mud
Post by: NI0C 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


Title: RE: Copying in the mud
Post by: AG1LE 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 (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 (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 (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


Title: RE: Copying in the mud
Post by: KH6AQ 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?



Title: RE: Copying in the mud
Post by: AG1LE 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




Title: RE: Copying in the mud
Post by: KH6AQ 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


Title: RE: Copying in the mud
Post by: N4BC on September 23, 2013, 08:12:58 AM
One thing I haven't seen mentioned in the thread is to use a headset. Audio from a speaker is OK with a strong, clear signal, but a headset will go a long way towards helping copy those down in the mud.

Dick K4FTW


Title: RE: Copying in the mud
Post by: W8DPC on September 27, 2013, 04:12:09 PM
This may not help any as I cannot remember the name of the program, but I swear that about 10 years ago I had a CW learning program that would let you insert white noise as you listened. I believe you could choose how much noise you heard, to simulate different conditions.  I'll look around and let you know if I figure out what it was.


Title: RE: Copying in the mud
Post by: AG1LE on September 27, 2013, 05:17:36 PM
This may not help any as I cannot remember the name of the program, but I swear that about 10 years ago I had a CW learning program that would let you insert white noise as you listened. I believe you could choose how much noise you heard, to simulate different conditions.  I'll look around and let you know if I figure out what it was.

Here is a set of audio files with -10 dB to +20 dB SNR @ 2kHz https://www.dropbox.com/sh/2j9chxsizxjeqgp/Gj97asYzpW (https://www.dropbox.com/sh/2j9chxsizxjeqgp/Gj97asYzpW) that I just created for testing a new Bayesian Morse decoder.  The files contain 50 WPM random text  (see random.txt on the shared folder) - 200 words of 5 letter/number each.

Let me know if these are useful.

73
Mauri AG1LE


Title: RE: Copying in the mud
Post by: WX2S on September 29, 2013, 10:06:27 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

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
I tried the APF yesterday -- had never used it before. Seemed to help.

Wx2s.


Title: RE: Copying in the mud
Post by: VK3HJ on October 12, 2013, 09:15:23 AM
I built an SDR rig about 3 years ago and find it fantastic for digging out the weak signals, and analysing the DX pileup. The spectrum display helps to find the active frequency quickly. I have the main Rx in both ears and the sub Rx in the right ear, for QSX up. For weak signals, or busy frequencies, I always use headphones. Phones help one focus on the signal.
Whilst I can adjust the DSP filter to any width, I tend to use 400 or 250 Hz.
As already mentioned, a receiving antenna for low bands is very helpful.
Another skill is riding the QSB. Make the most of the rising signal.
73,
Luke VK3HJ