Thanks to everyone for their input here. To clarify, the modem is a Harris RF-3466A. It has many options that are configurable. One option is a Mark Hold option. This option can be set to “OFF, ON, SWITCHED” switched means that the mark
tone is produced whenever the RTS (request to send) signal is asserted. On means on all the time. The way I have this setup was an attempt to avoid needing to manually switch between TX and RX with some switch or some such.
I set it up so that the exciter is set to VOX and the mark hold is set to SWITCHED. In this way the TX will automatically switch between RX and TX when the typing starts and stops and no other intervention is required. Kind of like a QSK
for RTTY.
In addition, there is a device (Black Box CAP) before the modem that does ascii-baudot conversion as well as 9600 bps to 45.45 baud conversion. This allows me to use a standard PC with a usb-serial dongle and a standard terminal program
and not have to worry about getting down to 45.45 baud or using a terminal program that supports baudot. This also lets me connect this 9600 baud/ascii channel to my serial console server which allows me to telnet to any serial device in the shack – including
this RTTY modem. Just very convenient.
This Black Box CAP device will buffer the data coming in a 9600 and it is set up to assert the RTS line to the harris modem when there is data present. So whenever a character comes from the terminal program, the CAP asserts the RTS line
and the modem produces audio for the character. When the character is done being sent, the audio drops and the transmitter reverts to receive mode (VOX). Works really well! But apparently won’t work for RTTY QSO (sad face).
One current workaround is if I type faster than 45.45 baud. The CAP device will buffer up to (I think) 8K of data. As long as there is data flowing on the 45 baud side, RTS will stay asserted and the audio will flow as expected.
If you want to see/hear how it is working currently, here is the end of a longer video showing it in operation:
https://youtu.be/2qJhX7wah_Y?t=1069
the whole Part 3 video that goes into the setup is
https://youtu.be/2qJhX7wah_Y
and there are two earlier parts of the project also available you in the link below if you’re interested.
So, based on everyone’s feedback, it looks like I have to figure out a secondary, out-of-band method to manually initiate the RTS when starting a transmission and manually release the RTS line when ending my transmission.
I have some ideas on this. But thanks everyone for their wisdom on this. I had a sneaking suspicion that my setup would not be good on the other side of the QSO.
From: W2HX
Sent: Friday, January 14, 2022 10:00 PM
To: '[email protected]' <[email protected]>
Subject: Mark Question
Hi all,
I’m still working on getting set up for RTTY at my QTH. I am planning to start with a glass tty set up, then get my M28s wired into the set up. I am using a 1980’s vintage Harris modem that converts RS-232 to audio tones and vice versa.
The way it is setup, when I type, I hear the mark/space transitions for each character. However, no audio is produced between the characters. Meaning no mark tone would be transmitted between characters.
Question: How big of a deal is this when doing RTTY? I know that some TUs might not recognize that there is neither a space nor a mark audio frequency present, and may produce garbage on the screen/printer. Or, do most operators use a mark-hold
function while receiving that would prevent (reduce) the garbage?
Bottom line, should I go with what I have? Or work hard to make sure a mark tone is present at all times between characters?
73 Eugene W2HX
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