The narrowest occupied bandwidth is to use 2Tone DOOK this takes up less
than 350Hz (that is at -80dB). There is also a slight receive decoder
advantage when using 2Tone as a decoder as it is a better spectral match
than 2Tone AFSK. 2Tone AFSK is a little wider at about 450Hz at -80dB.
Cannot really avoid it as it uses frequency modulation which comes with a
set of sidebands. DOOK is amplitude modulation of the individual tones.
Probably next best is Fldigi AFSK which is actually similar to 2Tone DOOK.
Dave and I corresponded on this some years ago. I can tell by looking at the
2Tone display if someone is using Fldigi or 2Tone DOOK or an AFSK or a radio
FSK system.
MMTTY AFSK with the transmit bandpass filter on and set for 512 TAP about
500/550Hz wide. Without the TX filter at 512 taps (this is not the default
setting) it is not much better than most radio FSK systems.
None of these AFSK/DOOK systems have timing jitter and so are good
performers.
2Tone FSK systems are a compromise. The pFSK requires external hardware to
convert a tone to a DC keying signal and has very low levels of timing
jitter. The TinyFSK that uses an Arduino is also jitter free. The FSK using
a COM port line has a lot of timing jitter due to the way Windows works. I
do not recommend it at all but put it in at popular request. This does cause
degraded decode performance. Why spend a lot of money on TX/PA/Antennas and
throw it potential performance away using this system?
Other systems that generate FSK from a COM port line all have timing jitter
and are not recommended including MMTTY/EXTFSK.
I have seen on my own SDR display some stations taking up 6KHz with all the
key clicks they have. On enquiry invariably they are using FSK with an old
ICOM rig. I am not sure about the newer ICOM rigs. Also many of the Yaesu
(all?) are very wide compared to 2Tone DOOK when using radio FSK mode.
I can only recommend K3 for use with radio FSK. There may be others as good
but not to my knowledge. However K3 is even better using AFSK/DOOK so might
as well use DOOK.
The safest bet is to use one of the AFSK/DOOK systems. Carefully ensure the
radio is not overdriven I use a 20dB resistive pad between the sound card
and the radio. The other advantage of using AFSK/DOOK is that it can be made
frequency agile so it follows the AFC value in other words where you are
receiving you also transmit. This reduces the offset to almost zero during
S&P and makes the RX tuning less critical. When in RUN mode the net facility
should be turned off so as other call you off frequency your TX does not
follow...
73 David G3YYD
From: Ktfrog007@aol.com [mailto:Ktfrog007@aol.com]
Sent: 24 October 2016 14:34
To: keepwalking188@ac0c.com; g3yyd@btinternet.com; rtty@contesting.com
Subject: 2Tone
Hi Jeff,
Which of the 2Tone RTTY keying methods are you referring to?
TX AFSK:
TX DOOK:
TX pFSK:
TX TinyFSK:
TX FSK:
73,
Ken, AB1J
In a message dated 2016-10-23 9:59:01 P.M. Coordinated Universal Tim,
keepwalking188@ac0c.com writes:
The Icom is a good radio but generally speaking the FSK waveform is pretty
(and in some cases amazingly) fat for that make especially. AFSK - or
better yet using David's 2Tone application for transmit on the other hand
would give you the best possible signal - and it's rig-independent!
Good luck on your gear hunt!
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
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