[digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31
Modem description from Peter G3PLX (the modem author): --- The modem is based on a raised cosine shaped tone filter response which has the property of zero ISI and zero adjacent tone interference with no sidelobes. Half the channel filter is in the tx and the other half in the rx, so it's often called root raised cosine because the channel filters at each end have a response which is the square-root of the complete filter. ---
[digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31
Yes, my note about bpsk/qpsk was nonsense. My understanding of theory is that baud equals the spread between tones in an OFDM or 2* baud in basic multi-tone signal. As someone noted, it is not ODFM. That does not fit with a 50 baud and 75 Hz separation. Compromise on total signal width and intersymbol interference. Vojtech
RE: [digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31
I think I am correct, and admittedly picky, to say that what is described is a form of source encoding with QPSK modulation. QPSK only applies to the modulation of two independent bit streams in a signal. A clear way of looking at this is that based on I/Q modulation the I carries one bit stream while the Q carries the other. The encoding below determine how the two bit streams are created. The URL did not work for me. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Andrew O'Brien Sent: Thursday, December 06, 2007 9:19 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31 On Dec 6, 2007 9:39 PM, Vojtech Bubnik [EMAIL PROTECTED] wrote: It is QPSK, not BPSK. 73, Vojtech And while on the subject of QPSK, here is an old article about PSK31 QPSK that I wrote around 2000 for the Logger32 help files, it includes quotes from Peter Martinez that he granted permission for me to use . Andy K3UK QPSK (Quaternary Phase Shift Keying) Operation Andrew J. O'Brien, KB2EOQ QPSK is referred to as an error-correcting PSK mode. Strictly speaking, it is not error-correcting in the traditional sense, but we'll leave that for another discussion. You will find it very useful in copying very weak signals. You will also discover that it is used less than BPSK. The usual convention among QPSK'ers is to use BPSK to establish a QSO and then switch to QPSK You will rarely find someone calling CQ in QPSK mode. Some radio amateurs will switch to QPSK if a BPSK QSO with weak signals is producing poor copy. PSK veterans will point out, however, that while QPSK outperforms BPSK when weak signals are the issue, QPSK will perform no better than BPSK if noise is the signal limiting condition. In the ancient, early days of PSK31, in the last century, QPSK was used as the mode of choice for some PSK nets, but that does appear to be the case in the 21st century. . Tuning a QPSK Signal snip QPSK can perform better than BPSK when band conditions are poor due to polar flutter. At such times you may be able to get copy from a QPSK signal even though the cross in the tuning window is poorly formed. Note: QPSK requires that BOTH stations in the QSO be using the same sideband! While this is not important for BPSK QSOs, it vital when using QPSK. QPSK-Reversed BPSK is demodulated the same way whether you are on upper or lower sideband. This is not true for QPSK, which operates like RTTY. You must shift the signal in a way that the decoder expects or it will not decode. In the case of QPSK, this leads to problems with standards, since the mode is so new. In actual practice, most hams appear to be operating BPSK using AFSK and upper sideband. This means that, when they switch QPSK (without reversing), they must be decoded by the other station using upper sideband and QPSK (without reversing). However, the standard of RTTY operation is lower sideband, and this means that most hams, operating as just mentioned, are operating QPSK-reverse, based on the RTTY standard. What this really means is that, when you and another station decide to switch to QPSK, if you do not know whether that station is using upper or lower sideband, there is a chance that you will not decode that station. If you click again on the mode pane, it will switch from QPSK to QPSK-reverse, and you should begin to copy. One trick is to set all three Rx windows on the signal to be copied, set one aux window at QPSK and the other at QPSK-reverse. When you see which Aux window starts to print readable copy, switch your main Rx window to that mode and you can then So What Is QPSK? How QPSK Got Its Name Peter, G3PLX, says in an article entitled PSK-31, A new radio-teletype mode with a traditional philosophy, says that he called it quadrature polarity reversal keying (which of course would have come out as QPRK), but that everyone else calls it quaternary phase-shift keying (QPSK). It is an error-correcting mode that relies on four phase-shifts rather than two, to create the basic scheme. Peter Martinez' (G3PLX) Description of QPSK The QPSK mode used in PSK31 takes the binary data-stream, at the point where it would otherwise go direct to the BPSK modulator, and feeds that through a 5-bit shift-register. A logic operation then forms the parity function of the 1st, 2nd, and 5th stages, and another forms the parity function of the 1st, 3rd, and 5th, giving two bit-streams at the same 31.25 bps rate as the original data. These two bits form a binary number, the four values of which are mapped to the four possible phase-shifts in the QPSK modulation. Thus a single data-bit from the source results in a 5-bit-long predictable sequence of 90-degree and 180 phase-shifts, interleaved with those of following and preceding bits. In the receiver, a Viterbi decoder is used to keep track
Re: [digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31
On Dec 6, 2007 9:39 PM, Vojtech Bubnik [EMAIL PROTECTED] wrote: It is QPSK, not BPSK. 73, Vojtech And while on the subject of QPSK, here is an old article about PSK31 QPSK that I wrote around 2000 for the Logger32 help files, it includes quotes from Peter Martinez that he granted permission for me to use . Andy K3UK QPSK (Quaternary Phase Shift Keying) Operation Andrew J. O'Brien, KB2EOQ QPSK is referred to as an error-correcting PSK mode. Strictly speaking, it is not error-correcting in the traditional sense, but we'll leave that for another discussion. You will find it very useful in copying very weak signals. You will also discover that it is used less than BPSK. The usual convention among QPSK'ers is to use BPSK to establish a QSO and then switch to QPSK You will rarely find someone calling CQ in QPSK mode. Some radio amateurs will switch to QPSK if a BPSK QSO with weak signals is producing poor copy. PSK veterans will point out, however, that while QPSK outperforms BPSK when weak signals are the issue, QPSK will perform no better than BPSK if noise is the signal limiting condition. In the ancient, early days of PSK31, in the last century, QPSK was used as the mode of choice for some PSK nets, but that does appear to be the case in the 21st century. . Tuning a QPSK Signal snip QPSK can perform better than BPSK when band conditions are poor due to polar flutter. At such times you may be able to get copy from a QPSK signal even though the cross in the tuning window is poorly formed. Note: QPSK requires that BOTH stations in the QSO be using the same sideband! While this is not important for BPSK QSOs, it vital when using QPSK. QPSK-Reversed BPSK is demodulated the same way whether you are on upper or lower sideband. This is not true for QPSK, which operates like RTTY. You must shift the signal in a way that the decoder expects or it will not decode. In the case of QPSK, this leads to problems with standards, since the mode is so new. In actual practice, most hams appear to be operating BPSK using AFSK and upper sideband. This means that, when they switch QPSK (without reversing), they must be decoded by the other station using upper sideband and QPSK (without reversing). However, the standard of RTTY operation is lower sideband, and this means that most hams, operating as just mentioned, are operating QPSK-reverse, based on the RTTY standard. What this really means is that, when you and another station decide to switch to QPSK, if you do not know whether that station is using upper or lower sideband, there is a chance that you will not decode that station. If you click again on the mode pane, it will switch from QPSK to QPSK-reverse, and you should begin to copy. One trick is to set all three Rx windows on the signal to be copied, set one aux window at QPSK and the other at QPSK-reverse. When you see which Aux window starts to print readable copy, switch your main Rx window to that mode and you can then So What Is QPSK? How QPSK Got Its Name Peter, G3PLX, says in an article entitled PSK-31, A new radio-teletype mode with a traditional philosophy, says that he called it quadrature polarity reversal keying (which of course would have come out as QPRK), but that everyone else calls it quaternary phase-shift keying (QPSK). It is an error-correcting mode that relies on four phase-shifts rather than two, to create the basic scheme. Peter Martinez' (G3PLX) Description of QPSK The QPSK mode used in PSK31 takes the binary data-stream, at the point where it would otherwise go direct to the BPSK modulator, and feeds that through a 5-bit shift-register. A logic operation then forms the parity function of the 1st, 2nd, and 5th stages, and another forms the parity function of the 1st, 3rd, and 5th, giving two bit-streams at the same 31.25 bps rate as the original data. These two bits form a binary number, the four values of which are mapped to the four possible phase-shifts in the QPSK modulation. Thus a single data-bit from the source results in a 5-bit-long predictable sequence of 90-degree and 180 phase-shifts, interleaved with those of following and preceding bits. In the receiver, a Viterbi decoder is used to keep track of all 32 possible combinations of guesses at the transmitted datastream, a running total of how well the received pattern of phase-shifts matches each guess. The clever thing about the Viterbi decoder is that it can be sure that if it throws out the worst 16 guesses before it receives the next signal (which doubles the number of to 32 again), it can never get it wrong, and after about 20 more signals, it can be pretty certain that its guess 20 signals ago was right. The snag is that it can only output its best guess after a delay of 20 signals, or 640mS in the case of PSK31. Longer Viterbi decoders are possible, but the amount of computation doubles at each extra signal delay, and for PSK31, which is used for live QSOs, the delay would be too long. More Facts to
Re: [digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31
You are picky AND correct! Andy. On Dec 6, 2007 10:33 PM, Rud Merriam [EMAIL PROTECTED] wrote: I think I am correct, and admittedly picky, to say that what is described is a form of source encoding with QPSK modulation. QPSK only applies to the modulation of two independent bit streams in a signal. A clear way of looking at this is that based on I/Q modulation the I carries one bit stream while the Q carries the other. The encoding below determine how the two bit streams are created. The URL did not work for me. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Andrew O'Brien Sent: Thursday, December 06, 2007 9:19 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Technical Question: FDMDV / QPSK in PSK31 On Dec 6, 2007 9:39 PM, Vojtech Bubnik [EMAIL PROTECTED] wrote: It is QPSK, not BPSK. 73, Vojtech And while on the subject of QPSK, here is an old article about PSK31 QPSK that I wrote around 2000 for the Logger32 help files, it includes quotes from Peter Martinez that he granted permission for me to use . Andy K3UK QPSK (Quaternary Phase Shift Keying) Operation Andrew J. O'Brien, KB2EOQ QPSK is referred to as an error-correcting PSK mode. Strictly speaking, it is not error-correcting in the traditional sense, but we'll leave that for another discussion. You will find it very useful in copying very weak signals. You will also discover that it is used less than BPSK. The usual convention among QPSK'ers is to use BPSK to establish a QSO and then switch to QPSK You will rarely find someone calling CQ in QPSK mode. Some radio amateurs will switch to QPSK if a BPSK QSO with weak signals is producing poor copy. PSK veterans will point out, however, that while QPSK outperforms BPSK when weak signals are the issue, QPSK will perform no better than BPSK if noise is the signal limiting condition. In the ancient, early days of PSK31, in the last century, QPSK was used as the mode of choice for some PSK nets, but that does appear to be the case in the 21st century. . Tuning a QPSK Signal snip QPSK can perform better than BPSK when band conditions are poor due to polar flutter. At such times you may be able to get copy from a QPSK signal even though the cross in the tuning window is poorly formed. Note: QPSK requires that BOTH stations in the QSO be using the same sideband! While this is not important for BPSK QSOs, it vital when using QPSK. QPSK-Reversed BPSK is demodulated the same way whether you are on upper or lower sideband. This is not true for QPSK, which operates like RTTY. You must shift the signal in a way that the decoder expects or it will not decode. In the case of QPSK, this leads to problems with standards, since the mode is so new. In actual practice, most hams appear to be operating BPSK using AFSK and upper sideband. This means that, when they switch QPSK (without reversing), they must be decoded by the other station using upper sideband and QPSK (without reversing). However, the standard of RTTY operation is lower sideband, and this means that most hams, operating as just mentioned, are operating QPSK-reverse, based on the RTTY standard. What this really means is that, when you and another station decide to switch to QPSK, if you do not know whether that station is using upper or lower sideband, there is a chance that you will not decode that station. If you click again on the mode pane, it will switch from QPSK to QPSK-reverse, and you should begin to copy. One trick is to set all three Rx windows on the signal to be copied, set one aux window at QPSK and the other at QPSK-reverse. When you see which Aux window starts to print readable copy, switch your main Rx window to that mode and you can then So What Is QPSK? How QPSK Got Its Name Peter, G3PLX, says in an article entitled PSK-31, A new radio-teletype mode with a traditional philosophy, says that he called it quadrature polarity reversal keying (which of course would have come out as QPRK), but that everyone else calls it quaternary phase-shift keying (QPSK). It is an error-correcting mode that relies on four phase-shifts rather than two, to create the basic scheme. Peter Martinez' (G3PLX) Description of QPSK The QPSK mode used in PSK31 takes the binary data-stream, at the point where it would otherwise go direct to the BPSK modulator, and feeds that through a 5-bit shift-register. A logic operation then forms the parity function of the 1st, 2nd, and 5th stages, and another forms the parity function of the 1st, 3rd, and 5th, giving two bit-streams at the same 31.25 bps rate as the original data. These two bits form a binary number, the four values of which are mapped to the four possible
