[RTTY] ARRL attack on current RTTY users

[Kok Chen]

On Nov 21, 2013, at 9:28 PM, Don Hill AA5AU wrote:

> So in other words, even though many of us are not against removing the symbol rate, for the sake of argument, we are to tell the FCC
> that we ARE in fact against removing the symbol rate in order to preserve the existing bandwidth regulation.

Don, there are a couple of points that can be made regarding higher symbol rates (By the way, if anyone finds these ideas to make sense and be useful, please feel free to adapt them for use in your own comments to the FCC.  I relinquish any copyright.):

1) increasing symbol rate has nothing to do with improving communications through HF propagation, instead, it all has to do with allowing certain high data speed implementations to be legal (including one commercial implementation that Joe W4TV has mentioned).  These are speeds well beyond a hundred of us can type at the same time.  

2) any bandwidth that is wider than 100 to 200 Hz can already handle selective fades, as easily demonstrated by our use of ATC in steam RTTY.  In fact, efficiencies suffer when you send higher bit rates since you have to handle errors from selective fades that can last for hundreds of milliseconds.  Any correction mechanism will need to have memory longer than the HF fade durations (which at a higher data rate means buffering lots more data), or it involves ARQ (which is in itself inefficient compared to ATC schemes).

3) when all else is equal (after your modulation/demodulation scheme can overcome the selective fading), a lower symbol rate will win over the same scheme at a higher symbol rate.  It is an intrinsic part of mathematics and mother nature.  Different modulation schemes can give you different Eb/No (basically SNR) performance, but given a scheme, the slower symbol rate will be better (there is less equivalent noise bandwidth for the same transmit energy per bit).

In an emergency, I would rather use a lower symbol rate and narrower bandwidth to call for help.  Unless I also need massive amounts of data to ask for help.

Although lower symbol rates can get through better, we will suffer (just from probability arguments) a greater chance of having our emergency communications disrupted by a wideband signal than we will from another narrow band signal.  Especially if the wideband signal comes from an automatic station that has no way of knowing if we, the narrow band station, is even asking for help (the situation today).

Anyway, you guys can massage the above better than I can.  English is my third language -- and it is getting worse with old age, especially since I no longer need to use it at work anymore after retiring :-P.

> My post to the reflector regarding the RM assigned to this proposal was sent to the moderator for approval (ARRL conspiracy?).

Nah, I am getting  through (I think :-).

> It's RM-11708 and so far I haven't found it up on the FCC site yet although I'm not 100% I'm looking in the right place.

Don, it is mentioned here at the FCC web site

http://apps.fcc.gov/ecfs/comment/view?id=6017477620

and the actual petition as filed, can be read here:

http://www.arrl.org/files/media/News/Petition%20for%20Rule%20Making%20AS-FILED%2011%2015%202013.pdf

73
Chen, W7AY