[GreenKeys] FSK shifts

[Harold Hallikainen]

Interesting discussion! I remember running 850 Hz shift in 1969.

Looking at FCC Rules for the Maritime Service, I find:

http://www.hallikainen.com/FccRules/2021/80/219/ which references ITU
documents.

Going back to 1986 when the maritime radio service rules were reorganized
into a single part 80, we find
https://www.govinfo.gov/content/pkg/FR-1986-09-02/pdf/FR-1986-09-02.pdf#page=161
. It refers to NB-DP (narrow band - direct printing) telegraphy. The shift
is 170 Hz. When an SSB transmitter is used, it is to be USB. The center of
the AFSK input is at 1.7 kHz with a shift of +/- 85 Hz. The higher emitted
frequency is to be space and the lower mark. This is opposite the amateur
LSMFT. The equipment "must be capable" of operation at 50 baud and not
exceed 100 baud.

>From Wikipedia ( https://en.wikipedia.org/wiki/Radioteletype ):
Due to the efforts of Merrill Swan, W6AEE, of "The RTTY Society of
Southern California" publisher of RTTY and Wayne Green, W2NSD, of CQ
Magazine, Amateur Radio operators successfully petitioned the U.S. Federal
Communications Commission (FCC) to amend Part 12 of the Regulations, which
was effective on February 20, 1953.[22] The amended Regulations permitted
FSK in the non-voice parts of the 80, 40 and 20 meter bands and also
specified the use of single channel 60 words-per-minute five unit code
corresponding to ITA2. A shift of 850 hertz plus or minus 50 hertz was
specified. Amateur Radio operators also had to identify their station
callsign at the beginning and the end of each transmission and at
ten-minute intervals using International Morse code. Use of this wide
shift proved to be a problem for Amateur Radio operations. Commercial
operators had already discovered that narrow shift worked best on the HF
bands. After investigation and a petition to the FCC, Part 12 was amended,
in March 1956, to allow Amateur Radio Operators to use any shift that was
less than 900 hertz.

Harold


> As many started using SSB transceivers that came with filters about 2.4
> khz  and 500 khz.   With audio tones of 2125 and 2975 hz as used on VHF AM
> and FM the 2975 hz tone would not pass very well on the ssb filter and not
> at all on the cw filter.   The 170 shift was just 850 divided by 4.  That
> would allow the tones to pass the 500 hz cw filter and I am thinking the
> audio filters were designed for a pass band of about 300 hz in the
> demodulator front end.
>
>
>
> It is interesting to be on the low bands with the oscilloscope on the
> tones and watch one tone fade in and out during bad band conditions.  I
> noticed that even with the 170 hz shift.
>
>
>
> Ralph ku4pt
>
>
>
>
>
> From: greenkeys-bounces at mailman.qth.net
> [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Russ Miller
> Sent: Sunday, August 22, 2021 12:09 PM
> To: N4TTY at arrl.net
> Cc: Green Keys
> Subject: Re: [GreenKeys] FSK shifts
>
>
>
> It was about 1968 when 170 Hz narrow shift became popular.  If you go back
> to RTTY Journal during that period, you will see the slogan "Broad
> minded?, Try narrow shift!"
>
>
>
> Why is narrow shift preferred?
>
>
>
> Here are some of the reasons: - narrow shift maes copy better with QRM.
> Period, end of discussion.
>
>
>
> Why technically? The ability to use a 500 Hz filter greatly improves the
> signal to noise ratio and helps eliminate adjacent station interference.
>
>
>
> 73
>
> Russ WA3FRP
>
>
>
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