Andrew O'Brien wrote: > I'm getting many public and private emails from around the world about > JT65A. Some seem to think I'm involved with the software and how it > was to be used for HF. I'm no expert and have only about 40% of the > software mastered at the moment. I have no more clue about HF > applications than anyone else, other than I may have been somewhat > responsible for getting the mode used more on HF. > > Keeping in mind that I am a total rookie, I thought I would attempt > to explain the very basics for HF use and respond to some of the many > emails I received today. > > JT65A is a mode within the WSJT software and , as Chris explained > earlier today, is an MFSK type of signal. The software was designed > for the very critical aspects of EME and meteor scatter applications. > An essential element of EME and Meteor work is weak signal detection > and careful timing of who is transmitting and who is receiving. > Another aspect is that a series of brief messages are transmitted in a > designated order, these essentially meet the accepted requirements for > a valid contact. These is usually the exchange of call sign, grid > square, and some confirmation of received signals. This would be the > equivalent of perhaps a PSK31 contact where the accepted protocol was > agreed that a valid QSO needed to include : Call sign, QTH, RST, and > acknowledgement that the other station received the sent information. > > Somebody suddenly started using JT65A on HF about 2 weeks ago, and us > JT65A ignorant hams simply detected a unknown mode on 20M. My only > involvement was to obtain the software when someone suggested it might > be JT65A and I confirmed the mystery signals were indeed JT65A. After > I mentioned it here and had a "QSO", a dozen or so hams jumped on > the mode , spread the word to others, and the HF applications appear > to have excited many hams. I have been amazed by the emails received > today from different parts of the world all indicated their first HF > JT65A QSO or reception. > > Early today, someone asked me just what can be done with this mode, is > it a legitimate communication application. Again, I'm no expert, but > I'll answer that with a big Y E S .You can do whatever you like with > it , you could in fact have keyboard chats if you wanted to. The > "standard" messages can be changed and you could type in " how's the > weather at your QTH", if you wanted to. It was not designed for this > , but you can do it. Remember, it was not designed for HF work at > all, so already someone has broken the mold . You can do likewise and > use it in anyway you see fit (within your Government's regulations). > > It is no different than Olivia, Hell, ALE, or MT63, in that it just > another mode. The user decides how it is best used. The one major > difference is that the software's default setting is that your typical > transmission lasts about 48 seconds and then you pause for 72 seconds > (12 seconds to the top of the minute and then 60 seconds allocated to > the responding station). > >>From a practical perspective, this mode appears to have uses that lean > toward the testing of propagation paths since the software always > gives you the SNR of a received station. The software records data > every minute, thus you can leave the software in monitor mode while > away from the shack and get a sense of the propagation upon your > return by looking at what was received, what the SNR was, and where > the stations received were located. > > If you are a ham like me, you might like the challenge of making a > contact but not really get in to the whole conversation thing. JT65A > suits people like this by keeping to a minimum exchange and moving > on. However, I will reiterate, you can use the mode to rag chew... > but it would be slow . It could be more efficient than other faster > modes though, since the throughput under poor conditions may be more > reliable than most other modes. > > So, play with it. Monitor . Invent new useful ways to use it. It > has been really great to see over 10 DXCC entities on HF JT65A in the > week since we have been "pushing" it. I wonder who will be the first > to get DXCC JT65A HF.? > >
As many may know, JT65 was originally written by K1JT(?). A paper on JT65 can be seen at http://physics.princeton.edu/pulsar/JT65.pdf and http://physics.princeton.edu/pulsar/K1JT/WSJT_User_600.pdf As far as I can tell, there is a very large use of FEC which of course cuts down on the amount of user data throughput. Additionally, with 65 tones, I believe that the signal is wider than 500 Hz. Hi Hi. "JT65A is generally used on 50 MHz." Thus JT65A on 6M is more like HF propagation...ot at least that on 14MHz and above. It would be wonderful if we could get K1JT to comment on the list for us. For those who are interested in reasons for wider bandwidths on HF, here is what K1JT says, reg. URL http://physics.princeton.edu/pulsar/K1JT/UpdateHistory.txt "1. In earlier versions the vertically-scrolling JT65 waterfall always displayed the frequency range 500-2500 Hz. The range has now been optionally expanded and made more flexible. By toggling a button labeled "BW" at the top of the SpecJT window you can change the displayed bandwidth to 4 kHz. In addition, you can offset the displayed region in 100 Hz steps by using buttons labeled "<" and ">", and you can return the range to its default alignment with a button labeled "|". This new feature provides two significant advantages. If your receiver provides a bandwidth greater than 2 kHz in USB mode, you can now display up to 4 kHz instantaneously (and with offsets, a total range of 5 kHz). The Kenwood TS-2000, for example, provides a 5 kHz bandwidth. The expanded range will make it easier to find other stations to work -- e.g. in contests, and at 1296 MHz where Doppler shifts are relatively large. In addition, extending the displayed spectrum to frequencies below 500 Hz is useful if you are using WSJT as a display tool when operating on CW." Does anyone know the actual transmit bandwidth of J65A? It would appear to be about 2 KHz wide. The bottom line is that Joe Taylor, K1JT, has provided some interesting code based I suppose in part on KA9Q's work, and perhaps that of Dr. Clark, which combined with the corporate knowledge of this group might produce a very robust mode with the possibility of much highere throughput. However, I believe that a new mode based on this or similar work will be considerbly wider than 500 KHz bandwidth. 73, Walt/K5YFW
