On Feb 13, 2007, at 7:42 PM, Don Hill AA5AU wrote:
> Chen, can you please confirm what USOS (Unshift on Space) is
> exactly and how it's done. It is my understanding that USOS returns
> the decoder to LETTERS after a space. If this is the case, then
> how can it be explained that I see a lot of "AA5AU TOO 001 001"
> reports where the signal report ends up in LETTERS but the actual
> serial number ends up in FIGURES?
(<Blush> Thanks for the kind words, Don.)
The sequence above that you saw can be explained this way...
If the sender is using USOS, s/he assumes that you are too.
So, to send the above exchange, he sends
AA<FIGS>5<LTRS>AU<SPACE><FIGS>599<SPACE><FIGS>001<SPACE><FIGS>001
The extra <FIGS> after each space is neccessary since the USOS
protocol assumes that both ends have turned their states to <LTRS>
right after the spaces.
The reason you printed TOO is because you missed decoding the <FIGS>
just before the 599. However, the neat thing about USOS is you have
a second chance to see another FIGS come by before receiving the 001
and yet another FIGS before that second 001.
My understanding is that USOS is really intended to help make text
messages print cleaner in case some character is decoded by mistake
as a <FIGS> -- i.e., right after the next space character, the system
reverts back to printing text instead gibberish.
Conveniently, <SPACE> is encoded by the octal 04 character in both
LTRS and FIGS shifts, otherwise USOS would not work very well.
I think it is an unintended consequence that contest exchanges also
improves by using USOS.
But.... not always...
Under the strict USOS rule, if you send "599 OR", the USOS
transmitter sends it as
<FIGS>599<SPACE>OR
which means that someone not set to receive USOS will receive it as
"599 94". If you are using USOS and you get repeated puzzled ??? in
return (especially in the Roundup where state and province
abbreviations are sent right after the RST), your software is using
this strict variant of USOS.
So, the above should have answered your other question:
> I've read that USOS has to be enabled on both the transmit and
> receive end.
The way to get around this, if you get repeated AGN AGN, is to send a
599OR with no space in between the 599 and the OR. This will force a
<LTRS> to be sent before the OR. Or, heh, heh, you can send a dash
before OR, i.e., 599-OR.
In fact, my favorite is to use "599-OR OR" if I am on software that
sends strict USOS. Yep, a dash can be very useful, and the space
between the two "OR" allows a USOS receiver a second chance to switch
to LTRS.
That said, I have also encountered software (in fact, I think there
may be more of this kind than the strict kind) that sends a <LTRS>
immediately after a space when USOS is in use, if the character
following the space is in the LTRS set, in which case "123 YO" is
sent as
123<SPACE><LTRS>YO.
Notice that both a USOS recipient and a non-USOS recipient will
decode that into "123 YO". The newbies who are not using USOS are
happy, USOS fanatics like W6WRT are happy. At the expense of a
slower exchange most of the time.
Unfortunately, I don't think the various RTTY software allow you to
select which variant of "USOS" to transmit with.
> I recall receiving bulletins and when we'd take a hit, the text
> would jump to the next line or return and
> type over the existing line. This NEVER happens in amateur RTTY.
> Why?
Hmmm, I think it should also happen with Amateur RTTY if you use
machines that obeys CR (carriage return) strictly, which no software
I know does.
If you are on a mechanical teletypewriter and an error bit causes
something else to turn into a CR, the carriage will move but the
platen will not advance, causing the previous line to be
overwritten. The platen of a TTY only advances when a LF is received.
I know that some 1970 era software TTY emulators will strictly obey a
CR. But I don't know any RTTY software that will allow a line to be
overwritten. It really not hard to do with systems such as MacOS X
that allow alpha channels.
> Final question. In today's ham RTTY programs, when you hit the
> ENTER key, do you send both a CR and LF characters (2 characters?).
> I'm thinking yes.
I know that cocoamodem outputs the CR/LF pair when you hit the enter/
return key. I have no clue what the others do.
On receive, cocoaModem will turn both CR and LF into new lines on the
screen, but if you receive a LF right after a CR, no extra line
advance is produced -- i.e., the CR/LF pair is treated as a single
newline character.
73
Chen, W7AY
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