Yes, after I sent the message I (re)checked and found that I switched mark
and space frequencies (due to some obscure reference I used. serves me well for
not checking).
* that mark is the higher (TX) frequency and also the frequency that you
are operating on
* space is the lower (TX) frequency.
And as you noticed Stefan and I use the right shift / mode.
Thanks for clearing this up.
Hi
Minto
On 06/03/2013 11:09, Minto Witteveen wrote:
Hmm might this be because ‘in the old days’ (amateur) RTTY was done with the rig in
LSB mode using AFSK?
Yes,
hence the confusion.
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…
No the
opposite MMTTY Assumes (Demands) (Instructs) LSB.
All others that I have
tested use the modern convention of USB for Digi Modes and the Mark is high
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 is
the same as fldigi
This then gets swapped around by fldigi because I listen (via
websdr) in USB… This explains why fldigi decodes me (and Stefan) just
right.
No swap it is already
correct.?
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)?
This from the author of
MMTTY and in the Help :-
You should understand the concepts of mark and
shift before operating RTTY.
Mark, Shift, and Space
Think
of a RTTY signal as a continuous, constant -amplitude,
suppressed-carrier
signal that shifts back and forth between two distinct
frequencies. RTTY signals
can also be seen as a combination of two CW
carriers at different RF frequencies,
only one of which is on at any given
time. The pattern in which the two tones
are transmitted is what codes the
letters.
One of these RF frequencies is known as the mark
frequency; the other RF frequency
is known as the space frequency. The
difference between Mark and space is known
as the shift. For amateur radio,
the shift has been somewhat standardized at
170 Hz. It is customary to refer
to the mark frequency as the frequency you are
operating on. For example, if
you say you are transmitting on 14085.00 kHz, that
means your mark frequency
is 14085.00 kHz and your space frequency is 170 Hz away.
This
brings up a question: Is the space frequency shifted 170 Hz. below the
mark
frequency, or 170 Hz. above the mark frequency? The answer to this
question is
established by convention. The ham radio convention is to operate
RTTY on lower
sideband, and to call one carrier the mark tone, and the other
carrier, shifted
170 Hz. (0.170 KHz.) below the mark tone frequency, the
space tone. A shift above
the mark frequency is called a reverse-shift.
Where Are the Tones?
The standard for posting
information on the location of a RTTY station is to post
the mark frequency,
but many posts are in error. When you operate AFSK using a
standard ham
transceiver, and use LSB mode, things get even more
complicated.
Here is an outline of what is happening:
You are operating AFSK, LSB (transmit and receive). The transceiver
frequency
display shows the location of your suppressed carrier. That is the
location where
a tone of 0 Hz. would be transmitted.
The transceiver
shows a frequency of 14080 kHz.
You have MMTTY set to use the HAM defaults,
with a mark frequency of 2125 Hz.
(2.125 KHz.) and a shift of 170 Hz.
(0.170KHz.).
You want to tell someone where your mark frequency is located,
or you tuned in a
station at this location, and you want to post its mark
frequency.
The mark frequency you are receiving is actually 14080 KHz. -
2.125 KHz.
= 14077.875 KHz. This last number is what you should post if you
want to post the
mark frequency on a DX Cluster.
Your space frequency is
shifted down another 0.170 KHz. from your mark frequency,
so your space
frequency is on 14077.875 KHz. - 0.170 KHz. = 14077.705 KHz.
73
Eddie
--------------------------------------------------------------------------
Ceterum
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
