[GreenKeys] FSK shifts

[Duncan Brown]

Thanks for all the comments on my question about FSK shifts.

I was not asking about the amateur change from 850 to 170 Hz shift. I 
understand the QRM reason for that change.

I was asking about why/when the commercial stations changed to 170 Hz. I 
apparently missed the FCC/ITU mandate for commercial stations to change 
to 170Hz shift.  I would think there would be a diversity advantage of 
850 Hz over 170 Hz and commercial stations would not have the QRM to put 
up with that we have on the amateur bands. Apparently, having more 
channels available for the commercials overrode any 850/170 hz 
advantage. Commercial shore stations could run more power and use space 
diversity to more than make up for the narrower shift that gave more 
channels.

have fun,

Duncan
K2OEQ

On 22-Aug-21 18:26, Richard Dillman wrote:
>
>
> On Sun, Aug 22, 2021 at 5:48 AM Duncan Brown <duncanancy at earthlink.net 
> <mailto:duncanancy at earthlink.net>> wrote:
>
>     I was surprised to learn that KPH is running 170Hz shift on RTTY and
>     that is now the standard for commercial RTTY/SITOR/NAVTEX.
>
>
> Greetings all.  We hope to resume testing on Saturday 9/4 on 12858.5 
> and 6324.5 starting at 1100 Pacific (1800Z) time with Baudot followed 
> by SITOR FEC.  TPO on both frequencies is 5kW using the original KPH 
> Henry HF5000D transmitters.  I hope that with longer notice more folks 
> will have a chance to listen.
>
> Regarding 170Hz shift, this is defined by the FCC emission designator 
> 300HF1B, the use of which goes back several decades to the 
> introduction of SITOR globally as a means of error correcting NBDP 
> (Narrow Band Direct Printing in FCC speak) for maritime 
> communication.  Almost all coast stations used this system as it 
> provided an automated means for ships to connect with the coast 
> station and send and receive messages without operator intervention.  
> While such use has almost completely disappeared, the USCG and the 
> coast guards of several other nations still use the FEC (forward error 
> correction) mode of SITOR for marine information broadcasts on HF as 
> well as MF for NAVTEX.  One can also still hear the channel markers 
> for stations like XSG, XSQ, TAH, etc., although it appears that 
> traffic is seldom passed.
>
> Best Regards,
>
> RD
>
>
> Richard Dillman
> Maritime Radio Historical Society
> https://www.radiomarine.org <https://www.radiomarine.org>
>

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