[GreenKeys] Autostart freq for 170 shift RTTY

[Ralph Mowery]

Just to add a few items to this.  

Rtty was allowed on the ham HF bands, but it was just a make and break
similar to CW and not the  two tones that have been used for many years.  I
think the audio two tones on AM was  legal on the old 11 meter frequency
before the hams lost it to the CB.
The VHF bands could use the audio so much of it was on AM and used the two
tones mentioned for that reason.

As many of the receivers and transmitters were not all that stable years ago
the FCC let hams use any shift up to 1000 Hz (cycles back then) so they
stayed at 850 shift for many years .  As the gear became more stable the 170
hz was used as it was 850 divided by 5.  Not sure why they used 5. 

ON HF any tone pair could be used as long as it was 850 or 170 hz
separation.   When ssb became more common and it was found that clean audio
put into the microphone input would generate signals like the two tone shift
and was legal.  I really hate it when people say AFSK on the low bands by
putting RTTY into the mic jack of a SSB transmitter as the result is not
really AFSK like it would be if AM or FM was used.  So the same gear could
be used on HF or VHF (which was usually AM or FM) the tones of 2125 and 170
or 850 up were used.  To generate clean tones out of the SSB transmitter it
is advised to stay above 1500 Hz for the mark so the 2nd and above harmonics
will be past the 2.2 or 2.5 khz ssb filter in many rigs.  

Ralph ku4pt


-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of w9ddd at tapr.org
Sent: Wednesday, December 30, 2020 5:41 PM
To: harold at w6iwi.org
Cc: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Autostart freq for 170 shift RTTY

Hi all,

I'll make some comments that aren't necessarily facts, bit tidbits that may
help trigger some one else's memory.
First amateur RTTY was only allowed on VHF and higher frequencies. Why 2125
and 2975.  The 850 shift was in use on commercial circuits. Some commercial
used 425 shift. 2125 is fifth harmonic of 425. 2975 is seventh harmonic of
425.  You can crate a frequency standard with a tuning fork (I made one).
Mark was probably low because a closed keyboard contact switches in more
capacitance, therefore lower frequency.  Not sure why space is low on HF.
Also inherited from commercial use?  Not much SSB in use at the time hams
were granted HF RTTY! Even less folks would have thought of using the SSB
mode of a transmitter to do RTTY in that era.

I'm still trying to remember how I did 14,070 auto start with a KWM-1 around
'71.  I remember I was shifting the PTO by making an adapter that plugged
the PTO tube socket, running in CW mode and dropping the drive level to keep
from overheating the finals.

John, W9DDD