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
|
|
