Re: stupid question


Justin Mattes--KC2GIK
 

I was thinking the same thing
Justin,KC2GIK

Charlie Trice, K8IJ wrote:


What are the chances of this RTTY thread going somewhere else?

Charlie, K8IJ

----- Original Message -----
From: "ve3iay" <ve3iay@rac.ca <mailto:ve3iay%40rac.ca>>
To: <070@yahoogroups.com <mailto:070%40yahoogroups.com>>
Sent: Saturday, February 13, 2010 12:42 PM
Subject: [070] Re: stupid question

RTTY uses a fixed-length 5-bit code that was originally developed for
electromechanical teleprinters that were used to send Associated Press news
items cross-country. Amateurs started RTTY by using surplus teleprinters,
and when computer RTTY first came in, it was made compatible with the older
equipment. The result is that RTTY continues to use the original character
codes and baud rates, even though there are very few of the original
teleprinters still in use.

A 5-bit code allows at most 32 characters. Take away the 26 uppercase
letters and there's not enough left for numbers and punctuation. A six-bit
code could have been used to get around this (64 characters), but that would
make every character longer, which would take more time to transmit. Since
numbers and punctuation are used much less frequently than letters, most of
the character codes in a six-bit code would be used only rarely and the
extra time for the sixth bit would be mostly wasted. Time is money in the
press business, and in the days when RTTY was originally developed, a more
efficient solution was looked for and found.

The solution was to make almost all of the characters do double duty,
similarly to the way the Shift key on a keyboard lets you change between
upper and lower case instead of requiring two separate keyboards. The two
"cases" in RTTY are called LTRS and FIGS, and you change case by sending a
"shift" character (LTRS or FIGS). In LTRS case, 26 of the codes are used for
the 26 letters (uppercase only). In FIGS case, the same 26 codes are used
for numbers and punctuation.

In LTRS case, the PTI key codes mean PTI. In FIGS case, the identical key
codes mean 058. If the FIGS control character is missed out for some reason
(e.g. noise or interference), the receive decoder will be in the wrong case
and it will print PTI instead of 058. This happens quite often, especially
under high QRM conditions.

To compound this, there are two different conventions about when to send the
shift characters when there are spaces between repeated strings of numbers,
and amateurs haven't been able to agree on which convention to use, or
whether and when to use dashes instead of spaces between numerical strings.

The bottom line is that RTTYers often find themselves having to decode the
letters on the top row of the keyboard as the corresponding numbers: TOO =
599, UE = 74, PPQ = 001 and so on. Most RTTY software has features to make
this a bit easier.

73,
Rich VE3KI

--- In 070@yahoogroups.com <mailto:070%40yahoogroups.com>, David Westbrook <dwestbrook@...> wrote:

PTI = 058 ..
qwertyuiop => 1234567890 ... that's the first letter row of the keyboard
and the number row ...

There's something about a shift in the way rtty works (and the way the
decoder's set up) -- i'm sure someone here will explain far better ..
it's
related to the debate of whether you should sent 599-001-001 or 599 001
001
or 599 001-001, etc .. the rtty@... listserv is a good resource
too -- that discussion comes up there occasionally (including
recently) ..

I wish i'd asked that "stupid" question months ago .. just recently
(from
the rtty list) realized that qwertyuiop=>1234567890 mapping, which now
makes
the "599PTIPTI" junk actually make sense!! Actually helped a couple
times
last night working the wpx-rtty test.

--david
KJ4IZW

On Sat, Feb 13, 2010 at 10:06 AM, Patrick Weatherford <
patricknw@...> wrote:



I was working the WPX RTTY contest this morning, and an Italy station
kept sending me "PTI" as his serial number. S9+10, clear as day, I
asked for several repeats and he kept sending PTI PTI PTI

Maybe I am ignorant, but what exactly is PTI?

Double checked Contesting.com, there is no other contest going on.

Patrick
AE5PW



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