Re: [digitalradio] Digital Mode tests this evening - FLDIGI
Hello Skip, On 4/16/2010 4:24 AM, KH6TY wrote: Hi Tony, The aircraft reflections are usually recognizable. They certainly are - especially at UHF. You can hear the pulsations in the background noise change in rate as the airplane flies around and sometimes even see the frequency shift on the waterfall, SBSpectrum (Peter Martinez) can reveal the inaudible Doppler shifts as well. I suspect the weaker, underlying Doppler you can't hear can cause interference with certain modes. Since Contestia and Olivia keep printing after the transmission has ceased, I suspect that the interleaving and redundancy is carrying enough data over the peaks and valleys that we hear to produce perfect print, but I am no theorist on this, for sure! Seems like a reasonable analogy Skip. It would be interesting to see these effects Skip. Feel free to send a few screen-shots. Thanks, Tony -K2MO Tony wrote: FWIW, PSK125R does not survive the Doppler disturbances on UHF. Olivia or Contestia does. Therefore, the mode we have found works best under the severe conditions of multipath, Doppler shift, Doppler spread, and very weak signals is Contestia 16-500 at 30 wpm. the minimum S/N is -12 dB, which is essential for weak signal UHF and VHF digital operation as every dB of S/N we can get is important for weak signal work. 73 - Skip KH6TY Skip, Thanks for the info. The path simulator results seem to agree with your observations on the high bands. I bet you have a fair share of problems with aircraft Doppler? I've noticed multiple reflections from multiple aircraft while monitoring VHF beacons. Spectrum analysis reveals how great those Doppler shifts can be; the mixing of 2 or 3 multipath signals can play havoc with throughput. . While it's not quite the same, we didn't get a chance to test on HF today. Andy tried his best to accomodate (always there for us Andy), but conditions weren't good between us on 80 meters. Tomorrows another day. Thanks again. Tony -K2MO __ Information from ESET NOD32 Antivirus, version of virus signature database 5032 (20100415) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com
Re: [digitalradio] Digital Mode tests this evening - FLDIGI
FWIW, PSK125R does not survive the Doppler disturbances on UHF. Olivia or Contestia does. Therefore, the mode we have found works best under the severe conditions of multipath, Doppler shift, Doppler spread, and very weak signals is Contestia 16-500 at 30 wpm. the minimum S/N is -12 dB, which is essential for weak signal UHF and VHF digital operation as every dB of S/N we can get is important for weak signal work. 73 - Skip KH6TY Skip, Thanks for the info. The path simulator results seem to agree with your observations on the high bands. I bet you have a fair share of problems with aircraft Doppler? I've noticed multiple reflections from multiple aircraft while monitoring VHF beacons. Spectrum analysis reveals how great those Doppler shifts can be; the mixing of 2 or 3 multipath signals can play havoc with throughput. . While it's not quite the same, we didn't get a chance to test on HF today. Andy tried his best to accomodate (always there for us Andy), but conditions weren't good between us on 80 meters. Tomorrows another day. Thanks again. Tony -K2MO Tony wrote: All, I'll be QRV for digital mode testing this evening after 2200z (April 15) till 0500z (April 16). QRG 14108 / 3588 (+ / - QRM). Modes of interest: 1. MFSK32 (Fldigi) 2. PSK250R (Fldigi) 3. MT63 1K (Fldigi) I've created a test transmission that will send each mode in sequence starting with MFSK32 and ending with MT63 1K (long iterleave). RS-ID will be used to facilitate automated band switching. Fldigi needs to be configured to do this: Click CONFIGURE IDs and UNCHECK RECEPTION DISABLES DETECTOR. This will enable automatic band switching upon the reception of RS-ID. The RX-ID located in the upper right corner of Fldigi's main window must be checked (green light). See you on Andy's sked page http://www.obriensweb.com/sked/ http://www.obriensweb.com/sked/ Thanks, Tony -K2MO __ Information from ESET NOD32 Antivirus, version of virus signature database 5031 (20100415) __ The message was checked by ESET NOD32 Antivirus. http://www.eset.com
Re: [digitalradio] Digital Mode tests this evening - FLDIGI
Hi Tony, The aircraft reflections are usually recognizable. You can hear the pulsations in the background noise change in rate as the airplane flies around and sometimes even see the frequency shift on the waterfall, but the big problem is that there is an almost constant, often fast, shift in frequency on UHF that causes the phone signal voice pitch to change in frequency so much and so fast that it is chopped up. That seems to be most prevalent when trying to cross several levels of propagation enhancement and signal are stronger due to the enhancement, but also when no enhancement is evident at all on the Hepburn maps http://www.dxinfocentre.com/tropo.html, and signals are weaker. If both stations are within the same level of enhancement, there is usually no problem, even if both signals are weak. Since Contestia and Olivia keep printing after the transmission has ceased, I suspect that the interleaving and redundancy is carrying enough data over the peaks and valleys that we hear to produce perfect print, but I am no theorist on this, for sure! In the case of PSK125R, you can see the carriers severely shifted in frequency on the waterfall and becoming jagged lines instead of straight ones. Decoding is perhaps 10% compared to Olivia and Contestia which will generally be 95% to 100% under the same conditions, depending upon the S/N. A CW note at the same time sounds like a buzz saw instead of a note. Even the very narrow Contestia or Olivia modes often fail, so we have found that 16-500 is the best compromise between sensitivity, speed, and bandwidth on UHF. Olivia or Contestia 8-250 theoretically should be 1 dB more sensitive, but usually have more errors than 16-500 when signals are near the noise threshold. The wider PSK250R and PSK500R modes, even though wider, are not usable because they require a greater S/N. We have been looking for a mode that will provide 24/7 coverage of our state (over a 120 mile radius) with reasonable antenna gains (14 dBi) and power (100 watts). HF does not do it because propagation changes over the course of 24 hours, 6M propagation is always very spotty, and often propagation, when there is no enhancement on 2M, is worse than on 70cm, so we are fortunate to find that Olivia and Contestia work well enough on 70cm to do the job. 73 - Skip KH6TY Tony wrote: FWIW, PSK125R does not survive the Doppler disturbances on UHF. Olivia or Contestia does. Therefore, the mode we have found works best under the severe conditions of multipath, Doppler shift, Doppler spread, and very weak signals is Contestia 16-500 at 30 wpm. the minimum S/N is -12 dB, which is essential for weak signal UHF and VHF digital operation as every dB of S/N we can get is important for weak signal work. 73 - Skip KH6TY Skip, Thanks for the info. The path simulator results seem to agree with your observations on the high bands. I bet you have a fair share of problems with aircraft Doppler? I've noticed multiple reflections from multiple aircraft while monitoring VHF beacons. Spectrum analysis reveals how great those Doppler shifts can be; the mixing of 2 or 3 multipath signals can play havoc with throughput. . While it's not quite the same, we didn't get a chance to test on HF today. Andy tried his best to accomodate (always there for us Andy), but conditions weren't good between us on 80 meters. Tomorrows another day. Thanks again. Tony -K2MO
[digitalradio] Digital Mode tests this evening - FLDIGI
All, I'll be QRV for digital mode testing this evening after 2200z (April 15) till 0500z (April 16). QRG 14108 / 3588 (+ / - QRM). Modes of interest: 1. MFSK32 (Fldigi) 2. PSK250R (Fldigi) 3. MT63 1K (Fldigi) I've created a test transmission that will send each mode in sequence starting with MFSK32 and ending with MT63 1K (long iterleave). RS-ID will be used to facilitate automated band switching. Fldigi needs to be configured to do this: Click CONFIGURE IDs and UNCHECK RECEPTION DISABLES DETECTOR. This will enable automatic band switching upon the reception of RS-ID. The RX-ID located in the upper right corner of Fldigi's main window must be checked (green light). See you on Andy's sked page http://www.obriensweb.com/sked/ Thanks, Tony -K2MO
Re: [digitalradio] Digital Mode tests this evening - FLDIGI
I will be there too. Andy K3UK On Thu, Apr 15, 2010 at 3:46 PM, Tony d...@optonline.net wrote: All, I'll be QRV for digital mode testing this evening after 2200z (April 15) till 0500z (April 16). QRG 14108 / 3588 (+ / - QRM). Modes of interest: 1. MFSK32 (Fldigi) 2. PSK250R (Fldigi) 3. MT63 1K (Fldigi)
Re: [digitalradio] Digital Mode tests this evening - FLDIGI
FWIW, PSK125R does not survive the Doppler disturbances on UHF. Olivia or Contestia does. Therefore, the mode we have found works best under the severe conditions of multipath, Doppler shift, Doppler spread, and very weak signals is Contestia 16-500 at 30 wpm. the minimum S/N is -12 dB, which is essential for weak signal UHF and VHF digital operation as every dB of S/N we can get is important for weak signal work. 73 - Skip KH6TY Tony wrote: All, I'll be QRV for digital mode testing this evening after 2200z (April 15) till 0500z (April 16). QRG 14108 / 3588 (+ / - QRM). Modes of interest: 1. MFSK32 (Fldigi) 2. PSK250R (Fldigi) 3. MT63 1K (Fldigi) I've created a test transmission that will send each mode in sequence starting with MFSK32 and ending with MT63 1K (long iterleave). RS-ID will be used to facilitate automated band switching. Fldigi needs to be configured to do this: Click CONFIGURE IDs and UNCHECK RECEPTION DISABLES DETECTOR. This will enable automatic band switching upon the reception of RS-ID. The RX-ID located in the upper right corner of Fldigi's main window must be checked (green light). See you on Andy's sked page http://www.obriensweb.com/sked/ http://www.obriensweb.com/sked/ Thanks, Tony -K2MO
