[RTTY] UPDATE Re: FSK Keying

[Ed Muns]

I have migrated to the TinyFSK implementation to avoid the Windows timing
irregularities that David summarizes here.

This is similar to the CW mode where a WinKey or other external hardware
keyer is used instead of direct logger keying.  The notable exception is
Win-Test which has somehow figured out how to have flawless CW keying via
the RTS/DTR signals on the radio CAT port without any external hardware,
with the Windows OS.

As to the transmitted signal width, this is a major problem with RTTY today.
A far too large number of signals take up 5-10 "channels" of bandwidth where
other QSOs could exist.  The insidious issue is that the offenders can move
in next to a narrower signal and never know it, while at the same time
causing tremendous QRM for the neighboring station.

This is due to either using FSK with a radio that is unfiltered
(unfortunately, most radios), or not using an AFSK method that is properly
filtered.  2Tone is fixed with the correct filtering but MMTTY defaults to a
much wider than needed bandwidth.  Most users are unaware and don't change
the default.  And, why should they change it?  By leaving it wide, they keep
their neighbors away from their operating frequency!

Fortunately, I use K3 radios that updated the firmware several years ago to
narrowly filter the FSK signal.  While a properly-adjusted AFSK signal may
be marginally narrower still, both are still far, far narrower than many of
the offending signals on the bands today.

But, the primary reason I transmit using FSK is that I do not trust my
ability to consistently maintain proper AFSK adjustment in the heat of
contest, using two or more radios while working stations on each of the two
receivers in each radio.  I fear that I will inadvertently get improper
audio levels that degrade my transmitted signal.  Part of this fear is the
Windows "surprise" we've all experienced where the OS changes the sound card
levels and other parameters from where we've set them.

Ed W0YK
_________________________________________________________________________

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of David G3YYD via
RTTY
Sent: 26 February, 2018 01:55
To: rtty at contesting.com
Subject: [RTTY] UPDATE Re: FSK Keying

Tim

AFSK will outperform serial port FSK at the receive end of the link. No
doubt about it because Windows is not and never will be a real time
operating system.

Windows internal timing causes the transitions between mark/space COM port
line to jitter in time from the 22mS per bit timing required for optimum
decode. As a result this increases the error rate of the decoder.

With AFSK the timing is set by the crystal clock that is driving the sound
card DAC( Digital to Analogue Converter) and therefore has no timing jitter.

The decoder error rate will be as low as it can be.

Further most radios FSK keying is unfiltered creating a very wide
transmitted signal that will cause avoidable QRM to adjacent frequencies. 
Using AFSK the filtering of the signal (in MMTTY the default should not be
used - TX filtering should be set to 512 taps) means that the TX will take
up a lot less bandwidth.

Better still is to use 2Tone DOOK (a version of AFSK) that is very narrow at
<350Hz at -80dB. Fldigi uses a similar scheme and while not quite as narrow
as 2Tone DOOK is very similar and narrower than MMTTY AFSK.

By the way do you think that RTTY is FSK? Many do because of what has been
written in the past. But look at how the decoders work and then match the
transmission to the decoder. All decoders treat the signal as two tone on
different frequencies. They use a narrow filter on each tone frequency - in
the case of 2Tone they are just 45.45Hz wide at -6dB. Then they
combine/compare the amplitude of those tones to decide if it is a mark or
space tone that was transmitted. Note this means each tone is treated as a
on/off keyed signal. In other words RTTY is really ASK (Amplitude Shift
Keying) or if you like OOK (on-Off Keying) So it is not FSK. Or as per 2Tone
Differential OOK (DOOK) as the tone are differentially keyed one going off
as the other comes on.

The best transmission system to use is the one that matches the decoder. 
2Tone and FLdigi do this.

73 David G3YYD

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of
groupsrichart at gmail.com
Sent: 26 February 2018 03:29
To: KenwoodTS-590 at yahoogroups.com; rtty at contesting.com; TS-590 at groups.io;
TS-590S at yahoogroups.com
Subject: [RTTY] UPDATE Re: FSK Keying of TS-590SG

Just to give everyone who has commented a little update:

1. I located another serial card and installed it in my computer. It gives
me a full -/+12VDC swing on the data lines.
2. The optoisolators in my interface are not pulling the PTT and FSK inputs
of the rig low enough to work. When the optoisolator is turned on, I am
still seeing +0.54VDC on the ACC2 inputs to the rig.
3. I tried different values of current limiting resistors from 100Ω to 1.5KΩ
on the inputs to the optoisolators with no change.
4. I checked my junk box for some NPN transistors and found none (I could
have sworn I had some 2N2222s), so I have a few on order for the coming
week. I plan to build the simple resistor/transistor interface that many
have suggested.
5. After I get FSK working, I do plan to also try AFSK. There seems to be a
spirited debate among many as to which is best. I have no doubt that either
method properly used can give good results so I want to find out
operationally which method I prefer.

My thanks to everyone who has taken the time to respond with your comments
and suggestions. I found them all very helpful.

73,
Tim WS4V

On 2/23/2018 2:49 PM, groupsrichart at gmail.com wrote:
>
> I would like to hear from anyone who is successfully keying the FSK 
> and PTT lines via the ACC2 connector on the rear panel of the 
> TS-590SG. What serial adapter and what hardware interface are you 
> using to do so?
>
> I have tried two different interfaces using optoisolators to attempt 
> FSK and PTT keying from a serial card to the rear panel ACC2 
> connector. Both attempts have failed. I am using MMTTY software for 
> keying and I do get the requisite signal change on TXD pin 3 (FSK) and 
> RTS pin 7 (PTT) lines. I have also verified proper setup of the '590 
> by manually grounding the inputs PKS pin 9 (PTT) and RTTY pin 2 (FSK) 
> on the ACC2 connector.
>
> However, I *think* the problem lies with the serial card not providing 
> enough voltage/current for the optoisolators to completely turn on and 
> provide a hard ground to the ACC2 inputs. I have tried two different 
> serial cards and one swings from -4.9 to +5.0 VDC on the data lines 
> and the other card swings from -3.8 to +3.9 VDC. The cards I am using 
> are a two port generic PCI Express SI-PEX15037 and a four port Perle 
> Fast 4 PCI card. Does anyone know of a serial card that has a full -12 
> to +12 VDC swing?
>
> One of the hardware interfaces has 4N25 optoisolators and the other 
> uses Fairchild FOD852 optoisolators. There are 1K series resistors in 
> the input line to the optoisolators and I have tried various values 
> (100, 220 & 470Ω) with limited success but nothing consistent.
>
> While my objective was to keep the rig isolated from the computer, I 
> am thinking about building an interface that uses NPN transistors for 
> keying. Is anyone using NPN transistors to key their '590? Are you 
> tying the ground from pin 5 of the RS-232 port to the pin 4, 8 or 12 
> ground of the ACC2?
>
> Any input is appreciated...I have been off RTTY since purchasing this 
> rig in November and I want to get back on the bands.
>
> Thanks,
>
> Tim WS4V
>

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