Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Or do they use a 3000 Hz BW for testing purposes and compare modes that way? Yes to compare. For example, I want to compare modes at S/N=-10 dB: I send a a signal of 1 mWatt and 10 mW of noise in 3KHz (so 3.33 mW per KHz). Now among this noise you can send your 1 mWatt signal in the way you want (RTTY, PSK...), the bandwidth you want (within 3 KHz) and also the coding you want. The judge will be the error rate: 2% is good, almost 100 % is bad. I guess you mean 2% character errors after going through the FEC mill? For pskmail ARQ to repair that efficiently you want an error rate of 1%. Anything worse generates lots of repeats or overhead through shorting of the packets. Fortunately we can often find a channel which is good enough by using the optimum band and/or going to a free frequency. 73, Rein PA0R Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ * Your email settings: Individual Email | Traditional * To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) * To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
Jose, Just as you were posting this message I was stumbling on a web site that agreed with your comment. With further searching I think I have the relationship. The QEX article has the statement that to go from the 3kHz bandwidth used you subtract 34 dB and add 10 log of the desired bandwidth in Hz. But I think he has it wrong. My search found that you adjust by taking 10log(BWoriginal/BWdesired) and adding it to the given figure. I think the author neglected to consider that the power of the signal is unchanged during the calculation. The result is you need to add 19.82 dB to the reported values to obtain the SNR for a 31.25 Hz signal. As proof (I hope g): Signal: 3000 Noise (3kHz): 3000 SNR(dB): 0 Signal: 3000 Noise (31.25Hz): 31.25 SNR(dB): 19.82 Where the noise is 1 Watt-s per Hz. The article reports that PSK-31 work down to -12 dB in AWGN this actually means it work to 7.82 dB. The channel capacity for that SNR per Shannon-Hartley is 88 bps. PSK-31 attains less that half the channel capacity. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jose A. Amador Sent: Friday, October 26, 2007 2:26 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation Yes, a 3 kHz voice channel...not the inmediate environment of the digital signal, but much, much farther away. And as noise floor is related to bandwidth... Your mileage may vary... 73, Jose, CO2JA
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Rud Merriam wrote: Jose, Just as you were posting this message I was stumbling on a web site that agreed with your comment. With further searching I think I have the relationship. The QEX article has the statement that to go from the 3kHz bandwidth used you subtract 34 dB and add 10 log of the desired bandwidth in Hz. But I think he has it wrong. I have not seen such article yet. My search found that you adjust by taking 10log(BWoriginal/BWdesired) and adding it to the given figure. Makes sense, in the way it takes the extra bandwidth into consideration. I think the author neglected to consider that the power of the signal is unchanged during the calculation. The result is you need to add 19.82 dB to the reported values to obtain the SNR for a 31.25 Hz signal. Seems to be in the ballpark. I had mentally derived some 17 dB as a correction factor, but did not actually calculate it. As Patrick explained, the 3 kHz bandwidth is a sort of equal yardstick to measure up the different modes. As proof (I hope g): Signal: 3000 Noise (3kHz): 3000 SNR(dB): 0 Signal: 3000 Noise (31.25Hz): 31.25 SNR(dB): 19.82 Where the noise is 1 Watt-s per Hz. The article reports that PSK-31 work down to -12 dB in AWGN this actually means it work to 7.82 dB. The channel capacity for that SNR per Shannon-Hartley is 88 bps. PSK-31 attains less that half the channel capacity. Seems it is time to dust off my copy of Sklar's book 73, Jose, CO2JA __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
RTTY is binary FSK so the bandwidth is approximately the deviation (170 Hz) plus the baud rate or 215 Hz. 73, John KD6OZH - Original Message - From: John Becker, WØJAB To: digitalradio@yahoogroups.com Sent: Saturday, October 27, 2007 01:04 UTC Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation How wide is 45 baud RTTY ? At 07:52 PM 10/26/2007, Rick, KV9U wrote in part: How do you make a wider bandwidth for a given mode? Isn't the bandwidth based on the baud rate to begin with?
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
The part that I don't fully understand is the bandwidth calculation. When I use PSK31, isn't the bandwidth pretty much set by the baud rate and width of the signal? Often it is expressed as around double the baud rate or ~ 60 Hz. Now if I have my rig wide open with the 3.6 kHz bandwidth and tighten it down to say 100 Hz, is this changing anything in terms of its practical ability to work deeper into the noise? Or do they use a 3000 Hz BW for testing purposes and compare modes that way? Doesn't this tend to favor the wider modes when it comes to claims of SNR? 73, Rick, KV9U Rud Merriam wrote: Jose, Just as you were posting this message I was stumbling on a web site that agreed with your comment. With further searching I think I have the relationship. The QEX article has the statement that to go from the 3kHz bandwidth used you subtract 34 dB and add 10 log of the desired bandwidth in Hz. But I think he has it wrong. My search found that you adjust by taking 10log(BWoriginal/BWdesired) and adding it to the given figure. I think the author neglected to consider that the power of the signal is unchanged during the calculation. The result is you need to add 19.82 dB to the reported values to obtain the SNR for a 31.25 Hz signal. As proof (I hope g): Signal: 3000 Noise (3kHz): 3000 SNR(dB): 0 Signal: 3000 Noise (31.25Hz): 31.25 SNR(dB): 19.82 Where the noise is 1 Watt-s per Hz. The article reports that PSK-31 work down to -12 dB in AWGN this actually means it work to 7.82 dB. The channel capacity for that SNR per Shannon-Hartley is 88 bps. PSK-31 attains less that half the channel capacity.
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
I took the dB results from the authors web page and calculated the bandwidth adjusted dB and the Shannon-Hartley channel capacity: Report SNRBWBW Adj Adjusted Capacity Mode (dB) (Hz) 10log(3k/b) SNR (dB) (bps) SSB 9 3000 0.009.00 9482 CW -155017.782.78 77 PSK31 -1131.25 19.828.82 97 PSKFEC -1231.25 19.827.82 88 RTTY -5 21511.456.45524 MFSK16 -13 316 9.77 -3.23177 MFSK8 -14 316 9.77 -4.23146 FeldHell-11 450 8.24 -2.76276 FMHell (105)-105517.377.37148 Olivia32/1000 -12 1000 4.77 -7.23250 Olivia8/500 -9 500 7.78 -1.22406 Olivia16/500-12 500 7.78 -4.22232 DominoEX11 -11 26210.59 -0.41245 DominoEX11FEC -13 26210.59 -2.41171 DominoEX8 -12 346 9.38 -2.62218 I took BW numbers from various web sites so if anyone disputes the values used feel free to tell me so. I can recalculate the values. I suspect that the BW used is sufficient to give a better feel for understanding the performance. In another message I see Rick wondering about the BW for PSK-31. I saw some other values reported but did not pursue that question and went with the conventional usage. For CW I just used a number for reasonable character speed. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Rud Merriam Sent: Saturday, October 27, 2007 1:47 AM To: digitalradio@yahoogroups.com Subject: RE: [digitalradio] Re: QEX Article on HF Digital Propagation Jose, Just as you were posting this message I was stumbling on a web site that agreed with your comment. With further searching I think I have the relationship. The QEX article has the statement that to go from the 3kHz bandwidth used you subtract 34 dB and add 10 log of the desired bandwidth in Hz. But I think he has it wrong. My search found that you adjust by taking 10log(BWoriginal/BWdesired) and adding it to the given figure. I think the author neglected to consider that the power of the signal is unchanged during the calculation. The result is you need to add 19.82 dB to the reported values to obtain the SNR for a 31.25 Hz signal. As proof (I hope g): Signal: 3000 Noise (3kHz): 3000 SNR(dB): 0 Signal: 3000 Noise (31.25Hz): 31.25 SNR(dB): 19.82 Where the noise is 1 Watt-s per Hz. The article reports that PSK-31 work down to -12 dB in AWGN this actually means it work to 7.82 dB. The channel capacity for that SNR per Shannon-Hartley is 88 bps. PSK-31 attains less that half the channel capacity. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jose A. Amador Sent: Friday, October 26, 2007 2:26 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation Yes, a 3 kHz voice channel...not the inmediate environment of the digital signal, but much, much farther away. And as noise floor is related to bandwidth... Your mileage may vary... 73, Jose, CO2JA Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
Sorry but I may have missed something. Your point is ? ? ? At 07:11 PM 10/27/2007, you wrote: I took the dB results from the authors web page and calculated the bandwidth adjusted dB and the Shannon-Hartley channel capacity: Report SNRBWBW Adj Adjusted Capacity Mode (dB) (Hz) 10log(3k/b) SNR (dB) (bps) SSB 9 3000 0.009.00 9482 CW -155017.782.78 77 PSK31 -1131.25 19.828.82 97 PSKFEC -1231.25 19.827.82 88 RTTY -5 21511.456.45524 MFSK16 -13 316 9.77 -3.23177 MFSK8 -14 316 9.77 -4.23146 FeldHell-11 450 8.24 -2.76276 FMHell (105)-105517.377.37148 Olivia32/1000 -12 1000 4.77 -7.23250 Olivia8/500 -9 500 7.78 -1.22406 Olivia16/500-12 500 7.78 -4.22232 DominoEX11 -11 26210.59 -0.41245 DominoEX11FEC -13 26210.59 -2.41171 DominoEX8 -12 346 9.38 -2.62218
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Hello Rick, When I use PSK31, isn't the bandwidth pretty much set by the baud rate The baud rate and the windowing (square, cosine...) chosen... down to say 100 Hz, is this changing anything in terms of its practical ability to work deeper into the noise? There will be no change if you have only gaussian noise, but if you have QRM it is another story. Or do they use a 3000 Hz BW for testing purposes and compare modes that way? Yes to compare. For example, I want to compare modes at S/N=-10 dB: I send a a signal of 1 mWatt and 10 mW of noise in 3KHz (so 3.33 mW per KHz). Now among this noise you can send your 1 mWatt signal in the way you want (RTTY, PSK...), the bandwidth you want (within 3 KHz) and also the coding you want. The judge will be the error rate: 2% is good, almost 100 % is bad. Doesn't this tend to favor the wider modes when it comes to claims of SNR? No it is indifferent. 73 Patrick - Original Message - From: Rick To: digitalradio@yahoogroups.com Sent: Sunday, October 28, 2007 1:20 AM Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation The part that I don't fully understand is the bandwidth calculation. When I use PSK31, isn't the bandwidth pretty much set by the baud rate and width of the signal? Often it is expressed as around double the baud rate or ~ 60 Hz. Now if I have my rig wide open with the 3.6 kHz bandwidth and tighten it down to say 100 Hz, is this changing anything in terms of its practical ability to work deeper into the noise? Or do they use a 3000 Hz BW for testing purposes and compare modes that way? Doesn't this tend to favor the wider modes when it comes to claims of SNR? 73, Rick, KV9U Rud Merriam wrote: Jose, Just as you were posting this message I was stumbling on a web site that agreed with your comment. With further searching I think I have the relationship. The QEX article has the statement that to go from the 3kHz bandwidth used you subtract 34 dB and add 10 log of the desired bandwidth in Hz. But I think he has it wrong. My search found that you adjust by taking 10log(BWoriginal/BWdesired) and adding it to the given figure. I think the author neglected to consider that the power of the signal is unchanged during the calculation. The result is you need to add 19.82 dB to the reported values to obtain the SNR for a 31.25 Hz signal. As proof (I hope g): Signal: 3000 Noise (3kHz): 3000 SNR(dB): 0 Signal: 3000 Noise (31.25Hz): 31.25 SNR(dB): 19.82 Where the noise is 1 Watt-s per Hz. The article reports that PSK-31 work down to -12 dB in AWGN this actually means it work to 7.82 dB. The channel capacity for that SNR per Shannon-Hartley is 88 bps. PSK-31 attains less that half the channel capacity.
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
This is to address the question of why a mode can work at -10 dB when Shannon-Hartley indicates this is not possible for that mode. The calculations adjust the reported dB for a 3kHz signal to the show the dB for bandwidth of the mode. This is the dB applicable for Shannon-Hartley. I lacked the ambition this evening to calculate the Eb/N0 for the modes to see how they compared on that basis. I just tossed in the theoretical channel capacity to show the theoretical capacity. The results are also applicable to the threads on possible new modes of operation. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Becker, WØJAB Sent: Saturday, October 27, 2007 7:16 PM To: digitalradio@yahoogroups.com Subject: RE: [digitalradio] Re: QEX Article on HF Digital Propagation Sorry but I may have missed something. Your point is ? ? ?
[digitalradio] Re: QEX Article on HF Digital Propagation
--- In digitalradio@yahoogroups.com, Walt DuBose [EMAIL PROTECTED] wrote: Rud Merriam wrote: After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net Rud, If you go back to the DCC presentation of KN6KB of a few years back on his new software modem...he measured the robustness of Pactor, MT63 and several other modes and Pactor wasn't that much more robust than MT63 at a -5 dB SNR. If I invested a $K Buck or so in Pactor III and WinLink, I'd claim it was the best thing since sliced bread...woudln't you? 73, Wa;t/K5YFW Hi Walt, Actually it is better if not many amateurs get a PTC-II modem since this way I and othe PACTOR 3 users have a better chance of connecting to a Winlink2000 PMBO and download our e-mail! Never thought about that have you? hi hi hi!!! 73 de Demetre SV1UY
[digitalradio] Re: QEX Article on HF Digital Propagation
PSK31 failed, bad copy even under good SNR, with 3 ms multipath and 10 Hz Doppler. It did not do well with 2 ms multipath and 1 Hz Doppler. Since Pactor uses PSK I wondered if it would similarly fail as shown by the PSK31 results. I suspect that it handles Doppler better through frequency tracking algorithms. PSK31 bandwidth is much lower than of PSK100 that Pactor 2/3 utilizes. PSK100 will lock to a signal 100/31 times far mistuned than PSK31. Symbol length of PSK31 is 32msec, symbol length of PSK100 is 10msec. I would say that PSK31 will be oblivious to 2ms multipath, but I suppose the phase difference of both reflections will not be stable, causing phase modulation of the summed multipath signal, which PSK100 with convolutional code will be able to handle. 73, Vojtech OK1IAK
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Something that has long been unclear to me is how can we have all these modes that work far below zero db S/N and yet the Eb/No (energy per bit relative to noise) can theoretically not go much lower than between 1 and 2 dB below zero dB according to the Shannon Limit? Then you need to take the value of the baud rate and bandwidth of the signal into consideration and that ratio is multiplied against the Eb/No. Wouldn't that further raise the required S/N ratio? We often see measurements of modes that work -5, -10, even -15 dB S/N? What are they measuring if not something related to the Eb/No? Pactor has proven the worth (necessity?) of using full time FEC and a moderate baud rate OFDM signal using PSK. Otherwise, you wouldn't you need some kind of training pulse sequence as used on the 8PSK MIL-STD/FED-STD/STANAG modems? 73, Rick, KV9U Vojtech Bubnik wrote: PSK31 bandwidth is much lower than of PSK100 that Pactor 2/3 utilizes. PSK100 will lock to a signal 100/31 times far mistuned than PSK31. Symbol length of PSK31 is 32msec, symbol length of PSK100 is 10msec. I would say that PSK31 will be oblivious to 2ms multipath, but I suppose the phase difference of both reflections will not be stable, causing phase modulation of the summed multipath signal, which PSK100 with convolutional code will be able to handle. 73, Vojtech OK1IAK
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Hello Rick, S/N in dB is measured versus a conventional noise bandwidth (3 KHz in general). This permits to compare modes against gaussia noise as you consider the signal power (indifferently of the way you modulate and the coding you use) and the noise power (the same for all modes). Eb/N0 is related to the SNR at the output of the matched filter (it is the energy of the bit / the energy of the noise in the equivalent noise bandwith for the duration of the bit). It is interesting to compare modulations vis-a-vis of the Shannon limit (-1.6 dB) but it is not what we finally need (S/N as defined above). 73 Patrick - Original Message - From: Rick To: digitalradio@yahoogroups.com Sent: Friday, October 26, 2007 8:39 PM Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation Something that has long been unclear to me is how can we have all these modes that work far below zero db S/N and yet the Eb/No (energy per bit relative to noise) can theoretically not go much lower than between 1 and 2 dB below zero dB according to the Shannon Limit? Then you need to take the value of the baud rate and bandwidth of the signal into consideration and that ratio is multiplied against the Eb/No. Wouldn't that further raise the required S/N ratio? We often see measurements of modes that work -5, -10, even -15 dB S/N? What are they measuring if not something related to the Eb/No? Pactor has proven the worth (necessity?) of using full time FEC and a moderate baud rate OFDM signal using PSK. Otherwise, you wouldn't you need some kind of training pulse sequence as used on the 8PSK MIL-STD/FED-STD/STANAG modems? 73, Rick, KV9U Vojtech Bubnik wrote: PSK31 bandwidth is much lower than of PSK100 that Pactor 2/3 utilizes. PSK100 will lock to a signal 100/31 times far mistuned than PSK31. Symbol length of PSK31 is 32msec, symbol length of PSK100 is 10msec. I would say that PSK31 will be oblivious to 2ms multipath, but I suppose the phase difference of both reflections will not be stable, causing phase modulation of the summed multipath signal, which PSK100 with convolutional code will be able to handle. 73, Vojtech OK1IAK
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
Rick, The measurement of SNR and Eb/No are two different measurements. The confusion comes because they are both cited in dB. It took me quite a lot of rereading material to clearly understand them. I dumped my understanding of it onto my web site at http://thehamnetwork.net/wiki/#Shannon-Hartley%20%5B%5BShannon%20Limit%5D%5D . To see the math and graphs clearly you need to have some support software installed. See http://thehamnetwork.net/wiki/#Graphics%20%5B%5BMath%20Expressions%5D%5D for details. The actual Shannon Limit is -1.6 dB for Eb/No. The limit for SNR is not expressible, that I have seen, as a single number. Instead it is determined by the power, noise, and bandwidth. More simply, by the SNR and bandwidth. One of the datum I found interesting is that below 0 dB SNR the channel capacity drops precipitously. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Rick Sent: Friday, October 26, 2007 1:39 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation Something that has long been unclear to me is how can we have all these modes that work far below zero db S/N and yet the Eb/No (energy per bit relative to noise) can theoretically not go much lower than between 1 and 2 dB below zero dB according to the Shannon Limit? Then you need to take the value of the baud rate and bandwidth of the signal into consideration and that ratio is multiplied against the Eb/No. Wouldn't that further raise the required S/N ratio? We often see measurements of modes that work -5, -10, even -15 dB S/N? What are they measuring if not something related to the Eb/No? Pactor has proven the worth (necessity?) of using full time FEC and a moderate baud rate OFDM signal using PSK. Otherwise, you wouldn't you need some kind of training pulse sequence as used on the 8PSK MIL-STD/FED-STD/STANAG modems? 73, Rick, KV9U
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
My understanding is that the Eb/No is more of what you would find at the antenna terminals, without the bandwidth of the receiver? Using your data on your web site, how does this relate to say, PSK31 modulation? Would the SNR also be at zero with the 31 bps baud rate with the B/C (Bandwidth in Hz divided by the Channel capacity in bps) at ~ 1.? Then how do you get the much lower SNR ascribed to a mode such as PSK31? ( ~ 10dB or so?) According to your chart it would need about 7 times the B/C ratio? I had thought the ratio would be somewhat fixed at about 63 Hz BW to 31 bps or around ~ 2.. What am I missing? The BW is actually much wider than the number we usually use for PSK31 to get the much lower SNR? How do you make a wider bandwidth for a given mode? Isn't the bandwidth based on the baud rate to begin with? 73, Rick, KV9U Rud Merriam wrote: Rick, The measurement of SNR and Eb/No are two different measurements. The confusion comes because they are both cited in dB. It took me quite a lot of rereading material to clearly understand them. I dumped my understanding of it onto my web site at http://thehamnetwork.net/wiki/#Shannon-Hartley%20%5B%5BShannon%20Limit%5D%5D . To see the math and graphs clearly you need to have some support software installed. See http://thehamnetwork.net/wiki/#Graphics%20%5B%5BMath%20Expressions%5D%5D for details. The actual Shannon Limit is -1.6 dB for Eb/No. The limit for SNR is not expressible, that I have seen, as a single number. Instead it is determined by the power, noise, and bandwidth. More simply, by the SNR and bandwidth. One of the datum I found interesting is that below 0 dB SNR the channel capacity drops precipitously. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
How wide is 45 baud RTTY ? At 07:52 PM 10/26/2007, Rick, KV9U wrote in part: How do you make a wider bandwidth for a given mode? Isn't the bandwidth based on the baud rate to begin with?
RE: [digitalradio] Re: QEX Article on HF Digital Propagation
Rick, Good questions. My only response right now is I dunno. g Back to the books. The QEX article based its results on a rate of 2% character error rate. PSK-31 with AWGN needed -11 dB. Crunching the numbers that at -10 dB you need a bandwidth of 227 Hz for 31.25 bps. At -11 dB would need somewhat more. Pushed to give some kind of answer I wonder if (1) since our received bandwidth is much wider than 31.25 Hz perhaps the sidebands are helping the situation and (2) is the reported SNR accurate? Additionally, for the latter is the SNR for just the 31.25 Hz bandwidth or for the entire received bandwidth? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Rick Sent: Friday, October 26, 2007 7:53 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: QEX Article on HF Digital Propagation My understanding is that the Eb/No is more of what you would find at the antenna terminals, without the bandwidth of the receiver? Using your data on your web site, how does this relate to say, PSK31 modulation? Would the SNR also be at zero with the 31 bps baud rate with the B/C (Bandwidth in Hz divided by the Channel capacity in bps) at ~ 1.? Then how do you get the much lower SNR ascribed to a mode such as PSK31? ( ~ 10dB or so?) According to your chart it would need about 7 times the B/C ratio? I had thought the ratio would be somewhat fixed at about 63 Hz BW to 31 bps or around ~ 2.. What am I missing? The BW is actually much wider than the number we usually use for PSK31 to get the much lower SNR? How do you make a wider bandwidth for a given mode? Isn't the bandwidth based on the baud rate to begin with? 73, Rick, KV9U
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
Rick wrote: Something that has long been unclear to me is how can we have all these modes that work far below zero db S/N and yet the Eb/No (energy per bit relative to noise) can theoretically not go much lower than between 1 and 2 dB below zero dB according to the Shannon Limit? That's right... Then you need to take the value of the baud rate and bandwidth of the signal into consideration and that ratio is multiplied against the Eb/No. Wouldn't that further raise the required S/N ratio? Actually, those negative SNR's are calculated on a 3 kHz (or similar voice channel) bandwidth. It does not tell the true story, but as a yardstick, it helps. We often see measurements of modes that work -5, -10, even -15 dB S/N? What are they measuring if not something related to the Eb/No? Yes, a 3 kHz voice channel...not the inmediate environment of the digital signal, but much, much farther away. And as noise floor is related to bandwidth... Pactor has proven the worth (necessity?) of using full time FEC and a moderate baud rate OFDM signal using PSK. Otherwise, you wouldn't you need some kind of training pulse sequence as used on the 8PSK MIL-STD/FED-STD/STANAG modems? 73, Rick, KV9U As I see it, Pactor does a whole lot more on the bandwidth it uses than the US_federal/military, non power limited standards. About the training sequence, the Viterbi demodulator ability to guess out the right bits out of the wrong received bits is another of the hidden Pactor II/III strenghts. Your mileage may vary... 73, Jose, CO2JA __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu
Re: [digitalradio] Re: QEX Article on HF Digital Propagation
I thought about the same. On pactor, the doppler perturbation is 31/100 of the signalling rate, thus, results less affected, even without taking into account the FEC and QRQ strenghts that Pactor also packs along. 73, Jose, CO2JA Vojtech Bubnik wrote: PSK31 failed, bad copy even under good SNR, with 3 ms multipath and 10 Hz Doppler. It did not do well with 2 ms multipath and 1 Hz Doppler. Since Pactor uses PSK I wondered if it would similarly fail as shown by the PSK31 results. I suspect that it handles Doppler better through frequency tracking algorithms. PSK31 bandwidth is much lower than of PSK100 that Pactor 2/3 utilizes. PSK100 will lock to a signal 100/31 times far mistuned than PSK31. Symbol length of PSK31 is 32msec, symbol length of PSK100 is 10msec. I would say that PSK31 will be oblivious to 2ms multipath, but I suppose the phase difference of both reflections will not be stable, causing phase modulation of the summed multipath signal, which PSK100 with convolutional code will be able to handle. 73, Vojtech OK1IAK __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu
[digitalradio] RE: QEX Article on HF Digital Propagation
After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: Rud Merriam [mailto:[EMAIL PROTECTED] Sent: Thursday, October 25, 2007 1:10 PM To: 'digitalradio@yahoogroups.com' Subject: QEX Article on HF Digital Propagation There is a great article in the QEX I just received (Nov/Dec 2007). The author is Daniel Crausaz HB9TPL in Switzerland. He reports on modeling and testing PSK, RTTY, Olivia, MFSK, DominoEx and Feld-Hell under various propagation conditions. I need to digest his work with respect to the OFDM proposal since the results indicate PSK may not be an optimal choice. Olivia works better under all the conditions tested. MFSK seems to be second. At first glance I would say this is because the transmission rate is so slow for Olivia at 2.5 character per second. I would find that painfully slow for even a chat mode. Interestingly, RTTY performs about the same under all the conditions tested. PSK either works well or just fails. It has problems in flutter conditions which seem to me be the conditions prevalent a lot of the time. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net
Re: [digitalradio] RE: QEX Article on HF Digital Propagation
Rud Merriam wrote: After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net Rud, If you go back to the DCC presentation of KN6KB of a few years back on his new software modem...he measured the robustness of Pactor, MT63 and several other modes and Pactor wasn't that much more robust than MT63 at a -5 dB SNR. If I invested a $K Buck or so in Pactor III and WinLink, I'd claim it was the best thing since sliced bread...woudln't you? 73, Wa;t/K5YFW
Re: [digitalradio] RE: QEX Article on HF Digital Propagation
One other comment. I have said before on this list that I have seen and used to have data produced by SouthWest Research Institute here in San Antonio that shows the maximim probable data capability of a single PSK signal. This study was done for the U.S. Government in research to find the best robust, medium throughput mode for a nation command alert system os some sort. I suspect it had something to do with always being able to keep the President informed under the most trying conditions with some sort of broadcast system. The upshot of all this as a limited discussion of a number of hams that were at the reporting session that the current MIL-STD modems could be improved on but that to obtain the desired throughput you would need more than the bandwidth associated with normal SSB transmitters. While amateur radio main not want a 4 or 5 KHz signal and the throughput that the government wanted, I think that a compromise bandwidth, something between that of PSK31 and perhaps 1 KHz with OFDM signal might be adequate for hams use on HF. As many have said before...if you REALLY want/need 100 error free copy, you are going to need an ARQ function and FEC. The trick is finding just how much of you signal you are going to give to FEC vs user data and how hard do you want to enforce ARQ. 73, Walt/K5YFW Walt DuBose wrote: Rud Merriam wrote: After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net Rud, If you go back to the DCC presentation of KN6KB of a few years back on his new software modem...he measured the robustness of Pactor, MT63 and several other modes and Pactor wasn't that much more robust than MT63 at a -5 dB SNR. If I invested a $K Buck or so in Pactor III and WinLink, I'd claim it was the best thing since sliced bread...woudln't you? 73, Wa;t/K5YFW
RE: [digitalradio] RE: QEX Article on HF Digital Propagation
I should have been more clear in my comment. The QEX article shows that PSK31 is terrible under conditions that induce phase changes. The MFSK16 and Olivia did much better. Even RTTY worked well under those conditions. PSK31 failed, bad copy even under good SNR, with 3 ms multipath and 10 Hz Doppler. It did not do well with 2 ms multipath and 1 Hz Doppler. Since Pactor uses PSK I wondered if it would similarly fail as shown by the PSK31 results. I suspect that it handles Doppler better through frequency tracking algorithms. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Walt DuBose Sent: Thursday, October 25, 2007 9:38 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] RE: QEX Article on HF Digital Propagation Rud Merriam wrote: After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net Rud, If you go back to the DCC presentation of KN6KB of a few years back on his new software modem...he measured the robustness of Pactor, MT63 and several other modes and Pactor wasn't that much more robust than MT63 at a -5 dB SNR. If I invested a $K Buck or so in Pactor III and WinLink, I'd claim it was the best thing since sliced bread...woudln't you? 73, Wa;t/K5YFW Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links
RE: [digitalradio] RE: QEX Article on HF Digital Propagation
Any chance of you locating that study information? I would like to use every technique possible to maximize the data in a 500 Hz signal. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Walt DuBose Sent: Thursday, October 25, 2007 9:51 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] RE: QEX Article on HF Digital Propagation One other comment. I have said before on this list that I have seen and used to have data produced by SouthWest Research Institute here in San Antonio that shows the maximim probable data capability of a single PSK signal. This study was done for the U.S. Government in research to find the best robust, medium throughput mode for a nation command alert system os some sort. I suspect it had something to do with always being able to keep the President informed under the most trying conditions with some sort of broadcast system. The upshot of all this as a limited discussion of a number of hams that were at the reporting session that the current MIL-STD modems could be improved on but that to obtain the desired throughput you would need more than the bandwidth associated with normal SSB transmitters. While amateur radio main not want a 4 or 5 KHz signal and the throughput that the government wanted, I think that a compromise bandwidth, something between that of PSK31 and perhaps 1 KHz with OFDM signal might be adequate for hams use on HF. As many have said before...if you REALLY want/need 100 error free copy, you are going to need an ARQ function and FEC. The trick is finding just how much of you signal you are going to give to FEC vs user data and how hard do you want to enforce ARQ. 73, Walt/K5YFW Walt DuBose wrote: Rud Merriam wrote: After a comment off list from Demeter I checked the Pactor specifications. It uses DBPSK or DQPSK. Why do the reports about Pactor indicate it is more robust than the QEX article would indicate? Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net Rud, If you go back to the DCC presentation of KN6KB of a few years back on his new software modem...he measured the robustness of Pactor, MT63 and several other modes and Pactor wasn't that much more robust than MT63 at a -5 dB SNR. If I invested a $K Buck or so in Pactor III and WinLink, I'd claim it was the best thing since sliced bread...woudln't you? 73, Wa;t/K5YFW Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links
[digitalradio] Re: QEX Article on HF Digital Propagation
Rud, How did DominoEx rate? 73, Steve N6VL
