[GreenKeys] WRU and SELCAL
Eric Scace K3NA
[email protected]
Mon, 26 Apr 2004 09:59:52 -0400
Suggestions:
1) Stick to "NNNN" (four "N") as the standard turn-off sequence, but programming the SelCal system to turn off on receipt of 3 Ns.
This takes one less slot in a stunt box. This has work successfully for decades on commercial and military RTTY circuits.
2) No need for double-LF in the sequences.
3) Why use [callsign]ZW for the WRU interrogation? What was wrong with the traditional "[callsign]Figs H Ltrs" followed by
immediate drop of carrier? The stuntbox would be set to respond upon receipt of [call] Figs H; the Ltrs was used as a buffer to
compensate for mechanical lag. (See page 17 of the "Teletype Model 28 Stuntbox" booklet.)
4) Given the scarcity of function bars, latches, forks, pawls, levers, etc., perhaps we could agree to use the last 4 characters of
a callsign as the actual selection sequence. For four-character calls like "K3NA", this amounts to a full call. But for "WB3ABC",
"3ABC" would be the sequence encoded into the stuntbox or its electronic equivalent. The cases of overlapping 4-character sequences
would be rare.
5) A complete SelCal system needs to define:
-- "conditioning code": the sequence of characters used to alert machines that call-directing codes are to follow. Upon receipt,
a machine is in the 'select non-print' state.
-- "call directing code" (CDC): this is what selects a machine to receive the message. Selected machines switch to the 'select
print' state.
-- "end of address code": this tells machines that all CDCs have been sent; if the machine hasn't been selected yet, it need not
pay attention to the message. All non-selected machines move to the 'non-select' state and don't pay any attention to anything else
until the next conditioning code is heard.
-- "end of message code" (EOM): this tells machines that were selected that the message has been completed. They can move to the
'non-select' state now.
An example of a commonly used approach:
conditioning code: twelve LTRS, five SP, CR CR LF. Note that normal message text would be unlikely to send a sequence of spaces
followed by a CR. The stuntbox might be encoded to use just four or three spaces, followed by one CR, to actually put the machine
in the 'select non-print' state. The twelve LTRS are sent to allow all the machines to get synchronized.
call directing code: last four characters of a callsign, or ZCZC (selects everyone).
end of address code: CR CR LF. Detection of CR CR or CR LF should be sufficient to put unselected machines into the non-select
state. For reasons discussed below, Figs H must also be interpreted as an end-of-address code.
end of message code: NNNN. Detection of NNN should be sufficient to put a selected machine into the non-select state.
6) If the above definitions are used, the WRU function can be:
12 Ltrs, 5 SP, CR CR LF Ltrs K Figs 3 Ltrs N A Figs H Ltrs (drop carrier).
This uses the conditioning code, CDC, and Figs-H as a WRU/end-of-address code. For the called station, Figs-H triggers the WRU
response. For the other stations, Figs-H places their machines in the non-select state because their CDC did not immediately
precede the Figs H.
As I recall, in the Model 28 world the WRU response was generated by a drum encoded with the response. I don't remember the
number of characters available on the drum, but it should be enough to send some number of Ltrs, CR CR LF DE [callsign]. The drum
clicked on right away after Figs-H was received.
========
Of course all of this can be imitated by computers or other electronic controllers. I detect that one of the desires of the
community is to use sequences which can be handled by traditional machines as well, which is why I made the above suggestions.
-- Eric K3NA
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Roy Norris
Sent: 2004 April 26 00:58
To: [email protected]
Subject: [GreenKeys] WRU and SELCAL
I have been searching the internet and old issues of RTTY Journal
looking for suitable designs for a WRU (answerback) and SELCAL design
that would serve our purposes for an auto start net. While this could
be done on a PC, my thought is that most would not want to keep a PC
running continuously to provide that function. WRU and SELCAL functions
can be provided in a model 28 stunt box arrangement however that
approach would require leaving the TTY machine on or the use of an
analog/TU based autostart which are notoriously sensitive to false
triggers by noise or off frequency signals and carriers.
It seems to me that an ideal solution would be an external,
microcontroller based box connected to the TU via an RS-232 port that
would provide the following functions:
1. PROVIDE DIGITAL AUTOSTART. - monitor the RS-232 output of the
TU and when a valid digital signal is present, close a relay that would
turn on the teletype machine. Turn off the teletype machine when an
"NNNN" is detected.
2. PROVIDE WRU CAPABILITY - monitor the RS-232 output of the TU and
when either the sequence "ZCZC" or (callsign)ZW was received, close a
relay which would key the push-to-talk switch on a transceiver and send
the following string to the TU
: " (20 diddles)(CR)(CR)(LF)(LF)(LTRS)(LTRS) DE (Callsign), (name),
in (location) (CR)(CR)(LF)(LF)(LTRS) NNNNN (CR)(CR)(LF)(LF)(LTRS)",
followed by turning off the relay which had activated the
push-to-talk switch.
3. PROVIDE MULTIPLE SELCAL - monitor the RS-232 output of the TU
and when any of several individually selectable code sequences were
received, close a relay that turns on the teletype machine.
Monitor for "NNNN" and turn off the relay that operates the TTY machine
when received. Codes would include a) ones for receiving a message
directed at that particular station (possibly use the station callsign
as a selcal trigger). b) a code for receiving bullitiens c) a code for
receiving "all-calls".. Each code would be individually activated by a
front panel switch so that an operator could choose to receive or not
receive messages addressed to his station, messages that were bulletins,
messages that were "all-calls".
All of this capability has been incorporated in various devices in the
past so there is nothing new here. I don't recall seeing it available
all in one external unit.
IIt would be wonderful if this capability could be incorporated in the
TTY Connect project currently underway by Gil Smith. I believe he has
made provisions for an optional microcontroller on the board he is
developing but I am not sure the board is designed so that it could
provide these functions. (What say, Gil??) Alternative, a small
inexpensive stand alone box could be designed using a microcontroller.
If there is anyone on GreenKeys that has the necessary skills and would
be willing to undertake the project, please speak up.
Alternatively, I will try and do it myself, although it has been 20
years since I did any programming of this nature and it was on 8085
computers, not microcontrollers. But I guess I could get back up to
speed in a couple of months. It would be tremendously helpful if I
could locate any of IRV Hoff's source code for his RMON program or his
standard teletype program that was use on the 20 meter autostart
frequency of 14.0875 Mhz. Does anyone on the list have this or have an
idea of where I might find it??
I have looked at the aforementioned RTTY12 program. It is written in
Basic and has selcal but no WRU that I can find. Irv Hoff's code would
be the best if we can find it. I hate that I threw away my copies some
years ago.
Thoughts? Suggestiohns ?? Ideas, pro and con ??
Best regards - Roy Norris, K4EEG
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