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

[Jeffrey Angus]

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