[RTTY] UPDATE Re: FSK Keying

Mon Feb 26 14:30:55 EST 2018

On 2/26/2018 1:45 PM, Ed Muns wrote:
> I have migrated to the TinyFSK implementation to avoid the Windows
> timing irregularities that David summarizes here.
In addition to TinyFSK, the microHAM Digikeyer II, microKEYER II, MK2R+
and micro2R (as well as the original microKEYER and Digikeyer) provide
hardware that avoids the Windows timing irregularities.

Further a *TRUE* UART based serial port (not USB) will avoid all but one
of the sources of timing irregularities.  Windows can not natively set
the data rate to a fractional baud rate.  That is, 45.45 baud (22 ms
bits) becomes 45 baud (22.22 ms bits).

> 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.
The third cause of "wide" RTTY signal (one that impacts all other modes
as well) is the terrible phase noise characteristics of many rigs.  All
Yaesu transceivers, Icom transceivers other than the 7850/7851, 7300 and
7610, Kenwood transceivers other than the TS-590/TS-990 and Flex "rigs"
prior to the 6000 series ALL have phase noise levels greater than -140 
dBc/Hz.  Some, for example, Yaesu FT-950, FT-991, FTdx1200, Icom 7600, 
7410, 9100, etc. have phase noise as bad as -120 to -125 dBc/Hz at 10 Hz
as measured by Rob Sherwood <http://www.sherweng.com/table.html>

73,

    ... Joe, W4TV

On 2/26/2018 1:45 PM, Ed Muns wrote:
> 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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