Ha Yes that is also what I remember from my early HAM days: in 1979 I wrote
an RTTY program for my apple II, and I also inserted plenty of lettershifts. One
single lettershift missed by the receiver might result in one or more lines with
useless figures...
I now insert a lettershift before ever space (I know that fldigi
automatically reverts to lettershift after a space, but anyhow). And also a ls
after each CR/LF.
Losts of activity now on 478.200+
73’s Minto pa3bca.
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Sent: Wednesday, March 06, 2013 20:09
Subject: LF: Re: Re: RTTY Protocol
Hi Minto the other trick when mechanicals were
around was always to transmit a figure as fs9ls even if another figure was
to follow. This ensures the machine doesnt slip into fs mode ....most text is
letters so the extra char doesnt use a lot of time..
Alan
G3NYK
----- Original Message -----
Sent: Wednesday, March 06, 2013 1:57
PM
Subject: LF: Re: RTTY Protocol
My PIC software now does the following when starting a RTTY
transmission:
* Start the TX (mark)
* wait 500 ms to ‘wake up’ the
receiver to the mark
* send two NULL characters to get the receiver in sync
(probably not necessary?)
* then (always) send a letter or figure shift
depending on the first ‘real’ character to transmit.
* then send the
text
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Sent: Wednesday, March 06, 2013 14:38
Subject: Re: LF: Re: RTTY Protocol
On
06/03/2013 13:14, Minto Witteveen wrote:
That settles it. The info I got (from an untrusworthy source it seems)
told me mark is 2125 and space is 2295. See my original message below.
But it is the other way around.
But it is only independent of the sideband used if both sender and
receiver use the same sideband.... You still have to agree.
And it seems that the current consensus is mark = highest tone =
highest frequency. So USB if AFSK is used. Yes
yes. BTW regarding missing the first character 's. In the mechanical
days did we not send CR/LF first to get things going? I have seen the software
have problems during the recent tests, printing Numbers instead of Letters.
This can be alleviated by sending 46RY first, 46 I think being RY with LetFig
set wrong. Eddie
73’s Minto pa3bca
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censeo Carthaginem delendam esse
Sent: Wednesday, March 06, 2013 13:57
Subject: Re: LF: RTTY Protocol
From my days on HF RTTY (~1970) with mechanical
'printers, the highest RF frequency was Mark (or idle tone) It was
independent of which sideband was used. I think this was also the mode used
by the commercial stations
Remember only European lines used bi-polar
signalling. The US used a 20mA mark and no current for space. A mechanical
machine of either type would chatter if the mechanism was not held in Mark.
Timing was mechanical and stop-start was necessary to maintain character
timing sync. with simple mechanical governors.
Alan G3NYK
----- Original Message -----
Sent: Wednesday, March 06, 2013 11:09
AM
Subject: Re: LF: RTTY Protocol
Hmm might this be because ‘in the old days’ (amateur) RTTY was done with the
rig in LSB mode using AFSK?
With mark at 2125 Hz and space at 2295 hz
and mark being the idling position, when using LSB the actual transmitted
frequencies would be ‘swapped’ (reversed)
So MTTY seems to assume rig
at USB, while all (all?) others assume LSB…
Still, Stefan and I seem to do RTTY wrong (i.e. amateur
reversed, as in AFSK on USB).
I just checked my PIC code and I have mark at high (DDS_BASE + 85
Hz) and space at low (DDS_BASE). This then gets swapped around by fldigi
because I listen (via websdr) in USB… This explains why fldigi decodes me
(and Stefan) just right.
This is of course based on the assumption that ‘right’ means
AFSK on LSB, that the space must be the high tone AND the low(est)
frequency.
What _is_ the consensus (if
any)?
73’s Minto pa3bca
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censeo Carthaginem delendam esse
Sent: Wednesday, March 06, 2013 11:44
Subject: LF: RTTY Protocol
Graham
Just confirmed
by test, MMTTY is backwards compared to all other Software. Others idle on
the high tone MMTTY idles on the low, unless the REV is
pressed.
From Wiki
the upper tone used
for idle condition (MARK).
Another site
says
You also have to switch the correct phase position (whether
the lower or higher frequency carrier in frequency modulation corresponds
to "Mark" or "space").
Mind you a Ham education site on the
subject says.
Remember that bfo’s help filter out the carrier waves
to allow for the original signals to come
through
Eddie
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