Re: [digitalradio] Another plug for JT65A ... the spectrum efficient mode
Spectrum efficiency must be measured in time necessary to get the info across, length of info transferred, and bandwidth. ((characters/second)/ bandwidth) or characters/(seconds * bandwidth). The bandwidth includes a certain guard band(minimum distance between 2 different signals), which for JT65 is quite small ... but the time is a large factor... To give a small example: Pskmail using PSK500 ARQ has a spectrum efficiency of 23/500 = 0.046 CPS/Hz ... measured on 14094.0 kHz running 100 mW connected to SM0RWO (1000Miles) ... The longest message in JT65 is 13 characters... and a message takes 48 seconds.. the bandwidth (according to the mode description) is 65 * 2.7 = 175 Hz ...which calculates to (13/48) / 175 = 0.001547619 CPS/Hz I would say this is a pretty bad value... :) Rein PA0R Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, I know many are already aware of this, but take a look N9DSJ-1 (EN52ti) Heard N6TE(DM12) on 3576.23 KHz -8dB at 03:32:00Z using JT65A N9DSJ-1 (EN52ti) Heard K3UK(FN02) on 3575.99 KHz -5dB at 03:32:00Z using JT65A Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, Andy K3UK http://www.obriensweb.com/digispotter.html Chat, Skeds, and spots all in one (resize to suit)Yahoo! Groups Links
Re: [digitalradio] Another plug for JT65A ... the spectrum efficient mode
But if the path S/N is so poor that you cannot get the message across at all, isn't the spectrum efficiency zero? ;-) 73 - Skip KH6TY Rein Couperus wrote: Spectrum efficiency must be measured in time necessary to get the info across, length of info transferred, and bandwidth. ((characters/second)/ bandwidth) or characters/(seconds * bandwidth). The bandwidth includes a certain guard band(minimum distance between 2 different signals), which for JT65 is quite small ... but the time is a large factor... To give a small example: Pskmail using PSK500 ARQ has a spectrum efficiency of 23/500 = 0.046 CPS/Hz ... measured on 14094.0 kHz running 100 mW connected to SM0RWO (1000Miles) ... The longest message in JT65 is 13 characters... and a message takes 48 seconds.. the bandwidth (according to the mode description) is 65 * 2.7 = 175 Hz ...which calculates to (13/48) / 175 = 0.001547619 CPS/Hz I would say this is a pretty bad value... :) Rein PA0R Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, I know many are already aware of this, but take a look N9DSJ-1 (EN52ti) Heard N6TE(DM12) on 3576.23 KHz -8dB at 03:32:00Z using JT65A N9DSJ-1 (EN52ti) Heard K3UK(FN02) on 3575.99 KHz -5dB at 03:32:00Z using JT65A Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, Andy K3UK http://www.obriensweb.com/digispotter.html http://www.obriensweb.com/digispotter.html Chat, Skeds, and spots all in one (resize to suit)Yahoo! Groups Links
Re: [digitalradio] Another plug for JT65A ... the spectrum efficient mode
Good point. What you have defined , Rein,is the occupancy efficiency in terms of time.. I was measuring efficiency in terms of bandwidth used. Obviously the othe rmeasure is wether the message was deleivered. Using 5 watts for a 300-400 miles trasmission on 80M at night , PSK250 may have needed sveral repeats to send 13 chracters . So even in term so time PSK250 may have been close to 0.001547619 . I'll do a test tonight. Andy K3UK On Wed, Mar 24, 2010 at 4:27 AM, Rein Couperus r...@couperus.com wrote: Spectrum efficiency must be measured in time necessary to get the info across, length of info transferred, and bandwidth. ((characters/second)/ bandwidth) or characters/(seconds * bandwidth). The bandwidth includes a certain guard band(minimum distance between 2 different signals), which for JT65 is quite small ... but the time is a large factor... To give a small example: Pskmail using PSK500 ARQ has a spectrum efficiency of 23/500 = 0.046 CPS/Hz ... measured on 14094.0 kHz running 100 mW connected to SM0RWO (1000Miles) ... The longest message in JT65 is 13 characters... and a message takes 48 seconds.. the bandwidth (according to the mode description) is 65 * 2.7 = 175 Hz ...which calculates to (13/48) / 175 = 0.001547619 CPS/Hz I would say this is a pretty bad value... :) Rein PA0R Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, I know many are already aware of this, but take a look N9DSJ-1 (EN52ti) Heard N6TE(DM12) on 3576.23 KHz -8dB at 03:32:00Z using JT65A N9DSJ-1 (EN52ti) Heard K3UK(FN02) on 3575.99 KHz -5dB at 03:32:00Z using JT65A Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, Andy K3UK http://www.obriensweb.com/digispotter.html Chat, Skeds, and spots all in one (resize to suit)Yahoo! Groups Links
Re: [digitalradio] Another plug for JT65A ... the spectrum efficient mode
Hi Andy, well, I don't agree... as soon as you talk efficiency, you have to define what that means. For me bandwidth efficiency is 3-dimensional, it defines how much information can be transferred within a certain time span, within a certain bandwidth. JT65A works with 65 frequencies, which are 2.7 Hz apart. So its bandwidth is 175, add to that 2 guard bands if you want to put a different mode close to it on both sides... You can put 2 JT65A signals very close together, because it uses a pseudo-random algorithm to make sure 2 JT65A signals (almost) never use the same concrete frequency at a certain point in time. As such it is quite bandwidth efficient. That changes completely when you would put a PSK signal that close, it would not work anymore. BTW, the comparison I showed was real... PSK500 has a raw speed of 48 CPS, and the net ARQ speed, including arq repeats is 23 CPS. Of course I cannot do it with 100 mW / 1000 Miles all the time, I need 5 Watts for an average connection. On 80m I have a stable connection to DA5UWG during daylight time using PSK500(down)/PSK500R(up). During the night I need MFSK32(down)/THOR8(up) for the same path... Nice thing abt PSkmail 1.0 is that you can start the connect in MFSK16, the system will decide to upgrade the speed/mode when possible, so you work in the most efficient mode most of the time. And BTW, it helps to use modes close to 500Hz bandwidth (PSK500, MFSK32, THOR22) when you use a 500 Hz (matched) filter :) Just wanted to express that looking at problems 1-dimensionally hardly ever reveals the full truth... 73, Rein PA0R Good point. What you have defined , Rein,is the occupancy efficiency in terms of time.. I was measuring efficiency in terms of bandwidth used. Obviously the othe r measure is wether the message was deleivered. Using 5 watts for a 300-400 miles trasmission on 80M at night , PSK250 may have needed sveral repeats to send 13 chracters . So even in term so time PSK250 may have been close to 0.001547619 . I'll do a test tonight. Andy K3UK
[digitalradio] Another plug for JT65A ... the spectrum efficient mode
I know many are already aware of this, but take a look N9DSJ-1 (EN52ti) Heard N6TE(DM12) on 3576.23 KHz -8dB at 03:32:00Z using JT65A N9DSJ-1 (EN52ti) Heard K3UK(FN02) on 3575.99 KHz -5dB at 03:32:00Z using JT65A Bill N9DSJ decoded two stations within 24 Hz of each other, how is that for spectrum efficiency? I was transmitting 5 watts, Andy K3UK
