[GreenKeys] Freqency shift standards and the HAL ST-6000 (And other rants)

[K0BX]

Nice trip down memory lane Jeff. 

On the PK-232 the shift was 200 HZ as that is what HF Packet was set 
for.  Soon many found that HF Packet was not very good but RTTY was great!

I  have an article on how to change the shift on the PK-232 to 170 HZ 
and optimize the filters for 170 shift.

Take a look at my website.

http://www.qsl.net/k0bx/align.htm

BTW I always wanted a HAL ST-6000 with the scope, but never found one 
that I could afford at the time.

Joe K0BX
on rtty for the past 33 years.  15KSR, 28KSR, 28ASR, 33ASR, 35ASR
ST-5/AS ST-6 with UT-4B, Dovetron MPC-1000, PK-232MBX
Now MMTTY with Rascal

Jeffrey Angus wrote:

>If my somewhat faulty at times memory serves me correct, the standard for 
>RTTY has been
>850 Hz (wide) and 170 Hz (narrow) shift since the time it was first allowed 
>by the FCC on
>amateur bands.
>
>Obviously the HAL ST-6000 has been optimized for these frequencies.
>
>I had always had problems with other stations running the AEA PK-232. (Back 
>when it was
>introduced in the early '80s) And I seem to recall that their idea of 
>"standards" were different
>from others. (I.e. everyone else).
>
>I went and dug up my old copy of a PK-232 manual and found this buried down 
>in the
>middle somewhere: Page 64 actually...
>
>3.4.1.6 Wide Shift IWIDESHFT)
>Use the WIDESHFT command to select wide (1000 Hz) or narrow (200 Hz) shifts.
>MARS stations will find WIDESHFT generally compatible with standard MARS 
>850-Hz
>shift Baudot RTTY operations.
>Nearly all amateuiradio VHF and HF Baudot and ASCII RTTY operators use 170-Hz
>shift. The PK-232's 200-Hz shift is within the passband and filter tolerances 
>of any RTTY
>demodulator in general service.
>
>Ah hah! I was right. 
>
>Considering that the used cost of a HAL ST-6000 was still holding a pretty 
>high value
>compared to the "new in the box" price of a PK-232 that would do other things 
>in 
>addition to RTTY, it explains why the sudden increase in "not right signals" 
>on the
>HF bands.
>
>Yet the people that owned the PK-232 terminals were steadfast that their 
>equipment
>was operating according the the standards. "It says so, right in the manual 
>it does."
>
>Well, they were operating according to standards. Bell-103 comes to mind, 
>except
>it was for 300 baud data over a phone line, and "adapted" as "close enough" 
>for
>use on RTTY.
>
>An excerpt from the Bell 103 specification:
>
>The Bell 103 standard frequencies of 1270 and 1070 Hz (originate mark and 
>space)
>and 2225 and 2025 Hz (answer mark and space)
>
>And again, digging into my questionable memory bucket, on RTTY the tones were
>2125 and 2975 Hz (850 Hz shift) and 2125 and 2295 Hz (170 Hz shift.)
>
>Obviously the reason AEA chose to play "close enough" with the frequency 
>shift 
>was they were using a Bell 103 Modem chip set. And the reasoning was most hams
>buying the PK-232 were interested in AX.25 packet radio. That it would do 
>RTTY 
>was extra, and not specific design criteria.
>
>I dug up my original copies of the Kantronics KAM manual and verified what I 
>thought 
>they were doing. By using capacitive switched filters for the decoding, they 
>could be
>set to any shift accurately. Although they default to 170, 425 and 850 Hz. 
>Much like
>the later model HAL ST-8000 with the shiny knobs. ;-)
>
>End of rant.
>
>This being the internet, I'm sure if I'm wrong, someone will be so kind as to 
>repeatedly
>stab me in the eye with a fork.
>
>Jeff-1.0
>wa6fwi
>
>
>
>
>
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