* 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
