Salvo
You have noticed the difference with Fldigi transmit. It uses differential
on/off keying (DOOK). That is it generates two tones and filters the
individual tones so they are both narrow in bandwidth before combining them
together. This produces a waveform that has considerable amplitude change
during the transition from one tone to the other as both tones are present
at the same time.
This system has some distinct advantages as long as the transmitter is
linear and produces a low level of IMD. It occupies a minimum of bandwidth
and even allows two signal to be received correctly with 85Hz off set
between them. As both tones are present at the same time a transmitter with
poor IMD will produce a wider signal than necessary.
2Tone for AFSK uses a different method, which is it filters the keying
waveform which then frequency modulates the carrier tone. This produces a
signal with no amplitude changes yet has a narrow overall bandwidth. But it
produces a much higher level of spectrum between the mark and space tones
than the DOOK method. But as there is no amplitude change and only one tone
at any instance poor transmitter IMD is not a problem.
2Tone originally used the DOOK method (and the code is still within the
software) but I changed to the one described above as being a better
compromise for those who will overdrive their transmitters so generating IMD
products. It is possible to set 2Tone to use DOOK by manually editing the
2Tone.ini file so that TXmode=1. However as soon as you change 2Tone set up
it will be overwritten.
In terms of transmit effectiveness - received character error rate - I have
found both DOOK and 2Tone FM system to have the same performance. In an
ideal world DOOK is the preferred method as it minimises spectral occupancy
but because a small minority do not know or wilfully misuse their kit I went
for the FM method as the default.
73 David G3YYD
-----Original Message-----
From: RTTY [mailto:rtty-bounces@contesting.com] On Behalf Of iw1ayd -
Salvatore Irato
Sent: 10 June 2014 22:53
To: rtty@contesting.com
Subject: Re: [RTTY] fldigi vs the others
Hi Bill and all.
I have no instrumentals or scientific evidences, but let me trow in my two
cents.
FLDIGI works pretty well. It's better ammunition is the AFSK TX, using a
K3 it result in a clear and crisp modulated AFSK signal. based on reports
and pictures by friends.
RXing is pretty well done but I am back within just a month or so and I
didn't tested it on worst case.
What is pretty amazing about noise immunity, it seems to me, is 2Tone.
Almost one year and half ago, it was several versions ago, I did a pretty
well JA RUN on 40m at the late evening here.
For who isn't acquainted to the EU side of the lower RTTY strip of the RTTY
sub band I could say it is a real nightmare. Our local late evening hours
are a bandwagon of PSK, CW and more exotic digital signal + several
different kinds of noise. Slow shifting carriers, some CW like
manipulations, static crashes and electrical wide band noise, name one and
be sure you have it or all well together on times.
Our region 1 RTTY sub band have a end at 7040, but 7035 is well used from
JA. Having a great tooling, a 2 el at 30m from ground, on 40m it is the most
pure joy when JA comes in. Well, even with the worst Russian single letter
pseudo beacon in betweens mark and space 2Tone is able to make you RUNning
as the hell.
I have been there several more times in other RTTY contests since then.
All the times with two 2Tone windows, one with standard filter and the other
with flutter filter I'd never miss a call. MMTTY is still there in the main
windows of the N1MM Logger setup. But it is quite not usable in all that
noisy, dirty and worst slice of the RTTY sub band.
2Tone continue to steam call by call with even the weakest signal with just
one tone. TOn times I have to shake myself as I didn't listened any RTTY
signal BUT one of the 2Tones windows is decoding valid calls and writing all
those onto the screen. ... One of the two 2Tone or each of the two with
slight better signals.
So far, it's my personal opinion that in a contest where I don't have the
time to switch and experiment with MMTTY profiles 2Tone is the most self
adaptive and thus effective thing - even better than the sliced bread.
BTW I eat a lot of sliced bread ;-) ...
Usually I RUN with K3 and 500 to 300 Hz filters. But also with a IC-7600 and
similar filters = same effect. But even wort audio, of course ...
Back on title, no way for fldigi, even if it is so effective it couldn't not
run 2 different filters algorithms on the same signal. But, anyway, I could
try using it together with N1MM Logger ... but running AFSK. on pileups.
Another way to think about the same kind of experimenting would be: how many
time I wish or would engage Dual PBT or TPF?
I suspect quite never with 2Tones as it work better in noisy environments,
some more hundreds Hertz give the better chances to decode even the weakest
signals ... I almost forgot that audio enhancing feature/s.
Sorry not to have A/B comparison by now. I will look forward on it.
73 de iw1ayd Salvo
PS I use almost the same N1MM Logger env. at home when not in PSK with
FLDIGI stand alone.
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