Hello Rick, >If often wonder if a mode that has a very wide ability to print even if >not tuned in well has to have some tradeoffs in robustness compared with >critical to tune modes. Anyone have specific information about that? The ability of DominoEx to be tuned very easily is that the modulation is an IFK one and not a MFSK one. It means that you measure a difference of frequency not a frequency in absolute as in MFSK. The good point it is easy to tune (no absolute reference of frequency) but the bad point is that when you do an error, the second symbol is also in error...you double the error (it's a bit like in PSK31, which one measures a difference of phase: if you do a error on one symbol, the next symbol will be also in error).
>Can anyone say with some degree of certainly what modes you think will >get through on the low bands with high QRN levels? I think Olivia must be good but Contestia is more close to ideal as twice quicker than Olivia with a minimum S/N just 1 or 1.5 dB superior to Olivia. 73 Patrick ----- Original Message ----- From: KV9U To: digitalradio@yahoogroups.com Sent: Friday, December 01, 2006 7:49 PM Subject: Re: [digitalradio] best mode to use for weak signal HF work and other mode discussions Brett, There are several sound card modes commonly used in addition to the most popular PSK31 and 45 baud RTTY That would be MFSK16, Olivia, Hell, and Throb/ThrobX. Although there are others, I rarely, if ever hear them. I no longer seem to hear any MT-63 and the CHIP modes came and went quickly. I wanted to do more experimenting with DominoEX and last night I got to work some 160 meter NVIS. We started out on MFSK16 but I have been having a lot of problems with this mode as of late and maybe it is because my soundcard is not calibrated correctly, but I find that I have to use about 10 to 20 Hz offset RIT in order to print the other station. MFSK16 really does require extremely accurate tuning of perhaps 4 Hz or so. My rig is an ICOM 756 Pro 2 which is supposed to have very good stability at 0.5 ppm. The other station and I tried some PSK31 for a short time when I lost him on MFSK16 and was just able to get him to try DominoEX at 11 baud. His signal was close to the noise although it was not that noisy on 160 since we are in the winter season. The print was very poor at 11 baud, so we dropped to 8 baud and things got better. Even at 8 baud, the speed of transmission is still faster than MFSK16. We had a CW station come up about 50 Hz below us and when that station was transmitting, it drastically affected the print of the DEX mode, even at 8 wpm. The one thing that DEX has going for it is that it is less critical to tune in. If often wonder if a mode that has a very wide ability to print even if not tuned in well has to have some tradeoffs in robustness compared with critical to tune modes. Anyone have specific information about that? We probably should have tried even slower speeds because later on I had great difficulty copying him and took lots of hits. He is running Linux so did not have the FEC version of DEX. My experience in the past was that the Viterbi coding helps a great deal in good printing, even at 11 baud, but of course your speed drops by all of 50% so you are just a bit slower at 11 baud/FEC than you would be with MFSK16. It would be interesting to hear of other station's experience with DEX and DEX/FEC and various speeds with and without FEC, particularly with the lower baud rates on low band NVIS type operation. One of the things that I have to accept is that almost none of these modes will work very well on the lower bands with high QRN levels from summer static. Can anyone say with some degree of certainly what modes you think will get through on the low bands with high QRN levels? 73, Rick, KV9U Brett Owen Rees VK2TMG wrote: > All, > > I find that I normally use PSK31 - as that is what most other stations > use > and is popular. But, I see a lot of stations that I cannot work - yet > I can > see their trace on the waterfall. Often, they are responding to my CQ and > they just don't make it. Why do people respond to a 2 * 3 call with a > 1*1 or > 1*2 call? There seems to be a strategy for psk31 mode that involves > sending > information multiple times - like a poor man's FEC. I expect that is why > they know who I am - from listening to my 2 * 3 call. > > The thing is - is there a mode that if I can see them on the waterfall > then > I can work them? I see no reason why we can't just go > narrower/slower/more > FEC and go right down into the noise. And why not have it be adaptive > - and > be able to become faster and wider if conditions are good - and even > have a > feature of being able to set a max bandwidth for those who may be > constrained or for where a number of stations are sharing a 2.4KHz > segment? > > Things I like about PSK31: > - easy to tune with start bars, idle bars and ending tail (sorry, my > naming > scheme here) > - narrow bandwidth > - popular > > Things I dislike: > - lack of RX sensitivity at times > - errors at low SN > > Features that would be nice: > - reliable, verified delivery > - ability to use as part of a 'stack' so as to use for APRS or TCP/IP or > file transfer or ALE or sounding or whatever > - easy tuning > - highly adaptive under trying conditions > - be basis of keyboard mode DX mode > - Open Source > > Please - I would like your opinions on this. Perhaps one of the current > modes could be adapted - or am I trying to re-invent the wheel? What > is the > best that is out there currently and can we make use of it? In an ideal > world what would be the theoretical best that we could aim for? I > understand > that with Turbo codes that it is possible to come very close to > theoretical > limits - are amateur protocols using such techniques? Having done some > reading about DominoEX there appears to be various workarounds which > may be > required in order to make a mode practical - like being able to work > around > a carrier on the frequency. > > 73 de Brett VK2TMG > >---------------------------------------------------------- > >No virus found in this incoming message. >Checked by AVG Free Edition. >Version: 7.1.409 / Virus Database: 268.15.3/562 - Release Date: 12/1/2006 > >
