CW Decode and Preamp?
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Please forgive me if this is a FAQ. If it is, just point me to where I can
find the old answer and I won't bring it up again. I can usually get the CW decode to work if I can clearly hear the signal. The CWT bar flashes and the text scrolls, and it gets a lot of characters right. BUT... ...that's only if I have the preamp OFF. I've tried using the preamp but decreasing the RF gain. I've tried using the preamp and the attenuator. I even tried setting a couple of bands to only 10db preamplification. But if the preamp is on AT ALL, the decode either never gets a "lock" and the CWT bar is flickering randomly (no matter what the threshold setting is) with no decode, or the CWT bar is solid, no flashing, and there's no decode. If have the preamp OFF, the same signal will usually decode at least somewhat, and sometimes excellently. Most of the time, W1AW can decode fairly easily...though FLDIGI and CWGET seem to decode more reliably. They'll decode 80-90%, while mush is appearing on the PX3 display lines. But at least I get something with the preamp off. But there's just some times when the signal is weaker and I can't get the threshold to crack without the preamp. But then I get no decode at all. Am I doing something WRONG? Is there some step that I'm not understanding? Heck, I've seen past entries in the list where some have said they can't get decode unless the preamp is ON! Or is there some known issue with preamp + decode that I haven't seen? Mind you, my antenna, while not fantastic, is adequate for me to get to Europe on FT8 at 35 watts. I even got from Philly to Fargo on 50w FT8 on 30 meters, using an indoor magnetic loop I built. So it's not my antennas. I have signal, but paradoxically, when the signal is strengthened by the preamp, I get lower decode performance. I'd expect that in high-noise conditions -- amplifying the noise as well as the signal and hashing them both -- but when the noise floor is low and the signal is just made more solid with the preamp, I should be able to decode it with the same technique as when I use it on a stronger signal without the preamp. Shouldn't I? Or am I simply not grasping some fundamental issue? I've read the manual, I've read mailing list archive messages, I've experimented with my own second rig on a dummy load sending a canned CW message (K2 s/n 1641). This will, I hope, be a moot point in a few months. I'm trying to learn to copy the CW barebrained instead of using the decoder. (I got rusty from when I first learned it back in 1999.) But I want to at least be able to check my copy using the decode function if I can until then. Between them, maybe I can hold a coherent QSO! Thanks, Gwen, NG3P -- -+-+-+-+- Jenny Everywhere's Infinite: Quark Time http://quarktime.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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I'd say initially that you aren't configuring the radio for the best
decode. Here's something I wrote some months earlier. It might prove worthwhile in your case. Of course not knowing what bands and your noise conditions is something you'll have to judge for yourself. You may need to change the TEXT DEC value to a lower or higher value. **************** As to RF gain, I find many hams do not understand the way to get enhanced performance from their radios. And this applies to most all legacy radios today. More RF Gain does not assure one they can or will hear weaker signals. The story is Signal to Noise ratio, namely in the area of the receiver noise floor. Since we can't change the RX noise floor, as it is established by design, then we need to change the signal coming into the radio. Typically one wants the no signal band noise to be some 10 dB above the noise floor of the receiver. And to do this we use a combination of attenuation and RF gain reduction. To run the math, if the RX noise floor is -135 dBm, typical of most modern radios, then the "sweet spot" for no signal band noise is -125 dBm or about S-1. The -125 dBm value is 10 dB above the receiver noise floor. If the no signal band noise is -97 dBm {S-5} then we need a combination of 28 dB attenuation and RF gain reduction. I typically use 15 dB attenuation and then back the RF gain down a good bit on 75M. While on 10M and 6M I will switch the attenuation off and engage the preamp. Running high gain and no attenuation just to see the S meter move upscale is just sucking up receiver headroom and certainly doesn't do anything constructive toward improving signal to noise ratio. Cranking up the RF gain and adding the preamp in many cases is the wrong way to go. I hear all the time about stations running the receiver preamp on 80/75 meters. WOW, they must have a really really low no signal band noise. Something like -135 dBm. In your dreams. ******************** Hope this helps. 73 Bob, K4TAX On 12/12/2018 7:21 PM, Gwen Patton wrote: > Please forgive me if this is a FAQ. If it is, just point me to where I can > find the old answer and I won't bring it up again. > > I can usually get the CW decode to work if I can clearly hear the signal. > The CWT bar flashes and the text scrolls, and it gets a lot of characters > right. BUT... > > ...that's only if I have the preamp OFF. > > I've tried using the preamp but decreasing the RF gain. I've tried using > the preamp and the attenuator. I even tried setting a couple of bands to > only 10db preamplification. But if the preamp is on AT ALL, the decode > either never gets a "lock" and the CWT bar is flickering randomly (no > matter what the threshold setting is) with no decode, or the CWT bar is > solid, no flashing, and there's no decode. > > If have the preamp OFF, the same signal will usually decode at least > somewhat, and sometimes excellently. Most of the time, W1AW can decode > fairly easily...though FLDIGI and CWGET seem to decode more reliably. > They'll decode 80-90%, while mush is appearing on the PX3 display lines. > But at least I get something with the preamp off. > > But there's just some times when the signal is weaker and I can't get the > threshold to crack without the preamp. But then I get no decode at all. > > Am I doing something WRONG? Is there some step that I'm not understanding? > Heck, I've seen past entries in the list where some have said they can't > get decode unless the preamp is ON! > > Or is there some known issue with preamp + decode that I haven't seen? Mind > you, my antenna, while not fantastic, is adequate for me to get to Europe > on FT8 at 35 watts. I even got from Philly to Fargo on 50w FT8 on 30 > meters, using an indoor magnetic loop I built. So it's not my antennas. I > have signal, but paradoxically, when the signal is strengthened by the > preamp, I get lower decode performance. I'd expect that in high-noise > conditions -- amplifying the noise as well as the signal and hashing them > both -- but when the noise floor is low and the signal is just made more > solid with the preamp, I should be able to decode it with the same > technique as when I use it on a stronger signal without the preamp. > Shouldn't I? Or am I simply not grasping some fundamental issue? I've read > the manual, I've read mailing list archive messages, I've experimented with > my own second rig on a dummy load sending a canned CW message (K2 s/n 1641). > > This will, I hope, be a moot point in a few months. I'm trying to learn to > copy the CW barebrained instead of using the decoder. (I got rusty from > when I first learned it back in 1999.) But I want to at least be able to > check my copy using the decode function if I can until then. Between them, > maybe I can hold a coherent QSO! > > Thanks, > Gwen, NG3P > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Gwen Patton
I'll take a look at both of those suggestions.
I do try to have the decode around 3 or 4, but code that'll decode with the preamp off doesn't even make the CWT bar flicker with it on. So there's more at work here than signal strength. That's why I asked what I did. But I'll try to work on technique and see if it's just me being thumb-fingered or something. On Thu, Dec 13, 2018 at 2:44 AM Gerald Manthey <[hidden email]> wrote: > Gwen > > If you hold down the Text Dec button (CWT) button what is your THR set to. > This is what you adjust for sensitivity for the decode. > > Mine is usually set to around 3 and I can decode from s4 to s9. If the > signal is real weak I usually Adjust the RF gain more and turn the THR down > to 2 and it will decode fine. > > I usually run with my RF Gain set at 3 o’clock all the time. > > There is a program that is called MRP40 that decodes almost no matter what > your radio is set to. One of the best decodeer programs out there. But it > cost. > > I used it at first and after using that and getting on the air it kinda > self taught me morse code. Hihi. > > Ok let me know if you have any other questions or if I can help. I hope I > understood the questions right and this helps. > > Thanks > > Gerald KC6CNN > > > > > > > > *From: *Gwen Patton <[hidden email]> > *Sent: *Wednesday, December 12, 2018 7:23 PM > *To: *[hidden email] > *Subject: *[Elecraft] CW Decode and Preamp? > > > > Please forgive me if this is a FAQ. If it is, just point me to where I can > > find the old answer and I won't bring it up again. > > > > I can usually get the CW decode to work if I can clearly hear the signal. > > The CWT bar flashes and the text scrolls, and it gets a lot of characters > > right. BUT... > > > > ...that's only if I have the preamp OFF. > > > > I've tried using the preamp but decreasing the RF gain. I've tried using > > the preamp and the attenuator. I even tried setting a couple of bands to > > only 10db preamplification. But if the preamp is on AT ALL, the decode > > either never gets a "lock" and the CWT bar is flickering randomly (no > > matter what the threshold setting is) with no decode, or the CWT bar is > > solid, no flashing, and there's no decode. > > > > If have the preamp OFF, the same signal will usually decode at least > > somewhat, and sometimes excellently. Most of the time, W1AW can decode > > fairly easily...though FLDIGI and CWGET seem to decode more reliably. > > They'll decode 80-90%, while mush is appearing on the PX3 display lines. > > But at least I get something with the preamp off. > > > > But there's just some times when the signal is weaker and I can't get the > > threshold to crack without the preamp. But then I get no decode at all. > > > > Am I doing something WRONG? Is there some step that I'm not understanding? > > Heck, I've seen past entries in the list where some have said they can't > > get decode unless the preamp is ON! > > > > Or is there some known issue with preamp + decode that I haven't seen? Mind > > you, my antenna, while not fantastic, is adequate for me to get to Europe > > on FT8 at 35 watts. I even got from Philly to Fargo on 50w FT8 on 30 > > meters, using an indoor magnetic loop I built. So it's not my antennas. I > > have signal, but paradoxically, when the signal is strengthened by the > > preamp, I get lower decode performance. I'd expect that in high-noise > > conditions -- amplifying the noise as well as the signal and hashing them > > both -- but when the noise floor is low and the signal is just made more > > solid with the preamp, I should be able to decode it with the same > > technique as when I use it on a stronger signal without the preamp. > > Shouldn't I? Or am I simply not grasping some fundamental issue? I've read > > the manual, I've read mailing list archive messages, I've experimented with > > my own second rig on a dummy load sending a canned CW message (K2 s/n > 1641). > > > > This will, I hope, be a moot point in a few months. I'm trying to learn to > > copy the CW barebrained instead of using the decoder. (I got rusty from > > when I first learned it back in 1999.) But I want to at least be able to > > check my copy using the decode function if I can until then. Between them, > > maybe I can hold a coherent QSO! > > > > Thanks, > > Gwen, NG3P > > > > -- > > > > -+-+-+-+- > > Jenny Everywhere's Infinite: Quark Time > > http://quarktime.net > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[hidden email] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to [hidden email] > > > -- -+-+-+-+- Jenny Everywhere's Infinite: Quark Time http://quarktime.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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Gwen Patton writes:
> I do try to have the decode around 3 or 4, but code that'll decode with the preamp off doesn't even make the CWT bar flicker with it on. I copy code in my head but have played with the CW decoder on my KX2 for amusement and also at our FD station so the others could see what was being sent and received. A couple were interested in learning the code. One fella brought an MFJ CW reader. We could not get a "solid copy" on either of them except on very strong signals. With typical band conditions and even sorta weak QRP stations, I can get maybe 80% copy - not bad, but not 100% copy. I've also found the threshold around 3-5 to be the best, like you, though does tend to change from station to station and day-to-day depending upon band conditions. > So there's more at work here than signal strength. The advice on better copy without excessive RF gain is valid. However, you do need that extra gain to properly drive the CWT and decoder on most signals, as you noted, even if the signal-to-noise ratio is compromised. Tuning and filtering is also important. I usually set my CW filter at 25-30Hz for best decode and push the button that sets the VFO to the proper offset to center the CWT ... then tweak the VFO just a bit for best decode. Lastly, I have found the decode to work better at 18-20 wpm or higher; slower code speeds is prone to triggering on noise. I would recommend tuning where there are no signals - just noise - and set things for no false decode from the noise, then tune to the station you want to decode. Hope the above helps. The decoder can be a good tool for helping you learn the code, just realizing you will seldom achieve 100% copy on the decoder (and sometimes even by ear!). I admire you for your desire to learn the code. It takes a lot of nerve to get on the air for those first few QSOs. We all remember our first QSOs. And as we'll all tell you, the best way to improve your CW is to get on the air. Most CW ops are more than willing to match your code speed (except in a contest maybe) to give you an enjoyable QSO and help you along. Sorry for the long reply, but hopefully helpful to you and some others. 72, Paul NA5N PS - email me if you'd like to arrange a sked on the air. Will use my straight key and any speed is fine. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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