Rick, ARQ is perfect for being sure emcomm and other messages are delivered error-free, but for chatting, most people will not want to slow things down waiting for an acknowledgment. Rather, they just ask for a repeat when it is needed. In addition, we can correct errors (a single apparently misspelled word, for example) with what we think is the right word, or fill in a missing word with our brains (since we can visualize things in context). Overall, this is usually faster than using ARQ and good enough for casual conversation.
However, for sending pictures, ARQ is sometimes absolutely necessary, especially with a compression technique in which a single byte ruins the whole picture. The Western Pennsylvania emcomm group has fully implemented NBEMS over both repeaters and simplex, but mostly over VHF, and, because VHF tends to be more constant and tends to be much more error-free than HF, did not want to spend the extra time (on any mode or speed) to slow down for ARQ, so we developed the Wrap program, which sends a checksum at the end of the message, and error-free reception can be verified that way. On our MARS emcomm net, MT63 on HF usually produces error-free copy on the statewide net, and Wrap is useful with MT63 also just for verifying that there were no errors, or indicating that a resend is necessary. However, far enough away, there may always be some stations, under poor conditions, that either need a repeat of the whole message, or need to have ARQ used to repeat bad blocks if there are many. The advantage of Wrap is that a one-on-one ARQ link is not needed except when that is the only way to get the message through. Bulletins can be transmitted in MT63 and received error-free by most stations, with others needing a resend, or perhaps a relay. On VHF SSB weak signal phone, it is common practice to use "vocal FEC" (to coin a term!) and just repeat callsigns twice or "over" twice to accomplish the contact during poor conditions. The standard call on CW is a 3x3 call, which is a type of "manual" FEC to try to get at least one of each callsign through. Most files these days are very large, compared to those in DOS days, and with the bandwidth limitations on HF, it just takes too long to send a very large file, even using a fast mode and ARQ, so I think there is little interest in file transfer on the bands either. Still, I have always though it would be very convenient to be able to send a schematic to explain something, but these days, that can be done with most stations by using the Internet. FAE400 is a great development, but the learning curve is too steep for emcomm operators thrust into a position without much training. That is why we elected to use commonly used digital modes and provide ARQ with flarq when necessary, and the learning curve is not as steep that way. ARQ definitely has its place, but is usually needed for messaging or when poor conditions require it (for example, if QSB is strong). I think that is why only a handful of hams have any interest in ARQ modes for chatting. That is how I see it. Other's opinions may vary, of course. 73, Skip KH6TY NBEMS Development Team Rick W wrote: > > > It seems that there are only a handful of hams who have any interest in > ARQ modes for chatting. There don't even seem to be many interested in > even using this for public service communications either and quite > frankly I am very concerned by this. > > There is nothing wrong with using older techniques and technologies, but > when breakthroughs occur that move us much farther along the path to > having the ability to both keyboard and send files error free for the > first time with a sound card mode, it tells you that hams really are not > interested in this after all. I have brought this up on a number of > other groups with nearly no response. > > FAE400 is not that new since it has been around for several years. Maybe > part of the problem is that it is only available on one program that is > less popular, but I have not been able to get much interest from other > multimode digital mode developers. > > 73, > > Rick, KV9U > > . > > -- *Skip KH6TY* http://KH6TY.home.comcast.net
