ICS AMT-1 User manual

ICS
AMT-1 Amtor Terminal Unit
USER MANUAL
l.C.S. Electronics Ltd.
PO BOX 2
ARUNDEL BN18 ONX
WEST SUSSEX
ENGLAND
Phone: (024 365) ~ S90
./
ICS AMT-1 Amtor Terminal Unit
User Manual - CW receive mod for
AMT-1 - AMT-1 Operating Guide -
AMT-1 Commodore 64 applications
operator manual

CONGRATULATION S ON YOU R PU RC HAS E OF AN AMT -1 .AJ.rroR TERMINAL U NIT. You WILL SOON HA VE ON E OF TH E WORLD 'S MO ST
ADVAN C ED H.F . R AD IO D AT A TR A NSMIS S ION SYSTEM S ON TH E AIR!
You shoula be able to get the AMT-1 running quickly and wi thout problems with any modetn SSB trans c eiver and any
ASCII RS232 termina l or personal computer which i s equipped wi th a serial i nterface, simpl y by reading th e
enclosed manual .
Below you will find a list of those transcei v ers and personal computers which are pre s ently known to go "first
time" with the AMT-1:
TRAN SCEIVERS
PERSONAL COMPUTERS
FT ON E TS
180
I TR 7 VIC 20
FL 101/
FT
707
FR 10 1
TS
520
T4XC BBC Model B
FT
901
TS
180S TS 515 T4B / R4B
ABC
80
FT 902 TS
930 TS
820
FT 227ZD
FT
lOlZD TS 130
TS 700 IC 701
FT
10 1 TS 830 TS
120V KWM 3 80
A number of ready debugged applications programmes for personal computer s already exist . Some of th os e f or the
mo re popular computers are enclosed, but I.C.S. ac tively solicits ap p lications inf o rmation from yo u for th e benefi t
of fu ture u sers.
Do tak e care with sy stem grounds and ensure adeuate cable screening to reduce hash radiation into your receiver.
If you h ave not already purchased a personal computer and ~ish t o use it with the AMT-1, check that a serial
interface is available f or it and that it can run full duplex at 110 or 75 Bauds at RS232 lev e ls. Mak e sure
that d ata c an be transmitted and received over the interface simultaneously and that CONTRO L and ESCAPE codes
can be sent from the keyboard . Oth erwise, y ou will have to use the CHRS command from Basic t o generat e these
c odes from other key d epressions.
Che ck ing y our sy stem ou t in ARQ mode
To
check out your sy stem on ARQ, tu ne y our transceiver ( on upper sideband ) to l4.075MHz ( the d ial reading
sho uld be around 14 .07 3.7) .
Then press control-A followed by one of the following selcals:-
GPLX (G3PLXl
HBAK
( HB9AK )
TDJT (
TI3DJT)
KRPA
(K4 PA )
KBBT
( KB6BT )
VAGE
(VK 2AGE)
Th ese stations are amongst th o se most active on AMTOR at the present time.
If the chosen station replies, type :-
(HIS CALL) de (Y OUR CALL) +?
If t he station requests further instructions type:-
HELP +?
In general, 14.075MHz should be avoided for long QSOs and used onl y f or specific ARQ calls.
O nce contact h as been established, both stations should Q SY up several KH z.
When calling CQ, you can call on 14 .075MHz in FEC m ode and QSY once contact has been made .
In many contr i es, there is also considerable AMTOR acti vity on 80 metres, c entred on 3.588MHz.
Don't f orget, if yo u call CQ in FEC mode, m ake sure y ou have fi rst loaded you r own selcal, so t h at yo ur
system will respond if called.
LATE N EWS
As the F.C.C. h ave ju st granted oermission for U .S . amateurs to use Amtor , WlAW is about to commence
broadcasting Amateur Radio N ews in Amtor FEC mode.

1.
2.
3 .
4.
5.
6.
7.
8 .
9 .
10 .
11.
CONTENTS
Introduction
Basic Theory
Getting the AMT-1 on the air
Operating Hints
Escape Codes
Control
Codes
Transceiver Connector
Terminal Connector
Front Panel Displa y LEDs
Internal Adjustments
Computer Interfacing w it h the AMT- 1
Cable Connections
Specification
Schematics
M icrocomputer Applications Programmes
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1
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5
Page 6
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6
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Page 8
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8
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9
Page 11
Page 12
Pages 13 - 15
Page 16

l. INTRODUCTION
The AMT-1 is designed to interface between an SSB
radio transceiver and an ASCII VDU, teleprinter,
or personal computer, using the error-correcting
system known as TOR or AMTOR.
Normal RTTY and ASCII transceive facilities are
also provided as well as cw transmit.
The interface to the transceiver is via an audio
input / output socket, which provides frequency-shift
keyed tone signals from the AMT-1 to the trans-
ceiver mike socket, and accepts received audio from
the transceiver extension speaker connector.
Th ere is also a keying line from the AMT- l to
switch from transmit to receive . This will
normally be connected to the "push-to-talk" line
on the transceiver.
All of these connections can normally be made
between SKl on the AMT-l and the transceiver's mike
or accessory socket.
The interface to the terminal sends ASCII serial
data from the AMT-1 for display or printing, and
accepts data in the other direction from the key-
board. These signals are represented by R.5232
logic levels.
M:>st terminals, or small computers which can be
used as terminals, will connect directly to the
AMT-l via SK2 . The AMT-l can be set to communic-
ate with them at either 75 or 110 Bauds.
Do NOT OPERATE YOUR TRANSCEIVER CCfffINUOUSLY
IN FEC oR Rm TRANSMIT f>'()DE wITHOUT FIRsT
REDUCING I TS OUTPUT TO UNDER HALF POWER.
SERIOUS DAMAGE TO YOUR TRANSCEIVER MAY OTHER-
WISE RESULT.
2. BAS IC THEORY
Teleprinter communication over radio links has
always been achieved via frequency-shift-keying
of the transmitter carrier frequency, the higher
frequency representing one logic level and the
lower, the other. In traditional RTTY, 32
characters are transmitted by various combinat-
ions of 5 data bits, transmitted serially and
preceeded by a start bit which synchronises the
receiver decoding. It is separated from the
followir,g character by a stop bit. This system,
although usually generated and decoded in modern
equipment electrically, was originally designed
to be decoded mechanically, and suffers from
problems when used on radio links which are
subject to fading and interference. Any such
interference or noise which causes a data bit
to be received in the wrong • polarity results in
an incorrectly printed character. Furthermore,
the start-stop technique used often results in
several characters being in error if a start-
bit is mutilated.
The conceptual basis of the TOR system is that
steps are taken to ensure that an error in the
received signal does not necessarily cause an
error in the output character. This is done by
transmitting extra information along with the
data, which enables the distant receiver to
detect the presence of errors. Instead of 5
data bits, 7 are transmitted. Three bits are
of one polarity and four are of the other.
The vast majority of randomly-occuring errors
result in this 3:4 ratio being altered at the
receiver,- enabling the receiving station to
detect that the data is erroneous.
There are 35 possible combinations of 7 bits, and 32
of these are translated directly to the standard RTTY
character set. others · are used as special control
characters. The start-bit mutilation problem is over -
come
by transmitting the data bits synchronously at
accurately-controlled intervals. The synchronisation
at the receiver is achieved by accurately-controlled
timing rather than by using a start bit.
There are two different types of communication avail-
able i n AMTOR: Forward Error Correction (FEC), and
Automatic Fequest (ARQ) . In the FEC mode, the 7-bit
characters are transmitted twice , and the receiving
station can choose which of the t wo passes the 3:4
ratio test . Up to half of the received codes can
therefore be in error before errors occur in the out-
put . The second transmission of each character is
delayed relative to the first, so that a prolonged
fade or burst of interference will only result in one
transmission of several characters being mutilated,
rather than both transmissions of a few adjacent
characters. EVen if both transmissions are mutilated,
the receiving station prevents an eJ:roneous character
being printed, suppressing the character completely
and signalling the presence of the error via the
ERROR lamp.
In ARQ mode, the transmitter sends a group of three
7 -bit characters in a block- The distant receiver
examines each one, and if any containes an error, an
automatic request to repeat the whole block is made.
In this case , the receiving station sends a repeat
request character to the transmitting station . In
this way interference or fading does not generally
result in errors, but merely a slowing-down of the
transmission of information each time a repeat is
requested. Data blocks and control-codes are trans-
mitted back and forth by the two stations working in
quick break fashion , usu~l!y en the same frequency.
Th is gives rise to the familiar chirp-chirp-chirp of
AMTOR signals on the air.
In both FEC and ARQ modes, accurate synchronisation is
essential between both ends of the link, and this is
achieved by special phasing signals transmitted at the
start of each contact, and maintained by crystal-
controlled timing.
In practice, it is possible for error& to occasionally
"beat" the 3:4 ratio check, and result in printed errors .
Nevertheless, FEC is considerably better than conventional
RTTY, and ARQ is very much better than FEC. The reason
for i ncluding both FEx:: and ARQ features is that ARQ can
only, by its nature, be used between two co-operating
stations, whereas FEC can be transmitted by one station
to any number of stations. Thus FEC is often used for
broadcast messages such as news bulletins and CQ calls .
In the ARQ mode, it is necessary to know
the iden t ity of the other station before establishing the
contact, hence FEC is often used at the start of a contact,
followed by a change to ARQ. The requirement to identify
the intended ARQ contact first arises from the initial
process which is required at the start of the contact.
This feature also enables the ARQ mode to be used to
selectively contact one particular station among a number
who may be monitoring a common frequency.
As well as the facility to transmit and receive FEC signals
and make or receive calls in ARQ mode, the AMT-1 has a
facility to enable it to monitor one side of an ARQ contact
between two other stations. This ability is not inherent
in the ARQ system itself, but is included since it is always
interesting to be able to listen-in to other contacts.
Apart from the AMTOR, the AMT-1 can also operate in conven-
tional RTTY mode both in transmit and receive. It can also
be used to send morse code (CW). The microprocessor in the
AMT-1 carries out code conversions and other processing, bu~
can be bypassed, allowing the ASCII terminal to connect
direct to the FSK modulator / demodulator and communicate in
ASCII over the air.

Page 2
3. GETTING THE AMT-1 ON THE AIR
This section acts as -a quick guide to the install-
ation and operation of the AMT-1. Those sections
which follow give more complete details, and may
be consulted after the basic system is working, or
whenever problems are encountered in getting the
system working properly. References given in
brackets refer to lat er sections where fuller in-
formation can be found .
The
AMT-1 shou ld be connected as follows:
SSS
TRANSCEIVER
D
~
o~
0
00 0
12v PSU
Jo f ORM YOUR OWN SELCAL
SIMPLY COMB I NE TI-iE FIRST LETTER, TOGETI-iER
WITI-i TI-iE LAST TI-iREE LETTERS OF YO UR CALL-
SIGN, THUS TI-iE SELCAL FOR WJ.AW SHOULD BE
!;MAW. THIS IS AN
11
UNOFFICIAL RULE" OF TI-iE
AMToR COl'MuNrTY!
HOME COMPUTER
OR ASCII
TERMINAL
D
! D D D D
SPKR
PTT
MIC .
I
it · 1
AMT -1 I D D D
L..
~~~~~~~~~-t.:~~~-T~E~R-M_l_N_A~L.....:. U _N~IT~~~~•o--~~~~~~~+
110 Baud RS232 ASCII
or 75 Baud
3~ . I POWER SUPPLY
A 12 -14 Volt power supply is required, capable of
providing 800mA. The negative side of the supply
should. be connected to the outer contact of the power
connecto r. The AMT-1 is protected against accidental
polar i ty reversal or overvoltage, but an incorrectly
applied voltage may blow the internal 1 Amp. fuse.
3 •2 TRANS . CE IVER CONNECTOR, SKl
This is a 7-pin socket, although a 5-pin DIN plug
can be used in it. Pin 1 is the audio input from
t he transceiver, and should be connected via a
screened cable, the screen of which should be
taken to pin 2. Pin 3 is the audio output from
the AMT-1 to the transceiver (u sually to the MIKE
sock . et) and should be similarly screened, with
the . ·s· creen taken to pin 2. An internal pre-set
(RVl) can be used to vary the audio output level,
although an external attenuator may be needed to
reduce the level in some cases (7 . 3). Pin 5 is
the transmit-changeover line from the AMT-1 to
the "p ush-to-talk" line on the transceiver. In
most cases all of the connections from SKl can be
made to the MIJ<E · ~ocket of the transceiver, the
speaker output of the transceiver being taken to
a spare · pin on the MIKE socket. The connections
and signals levels for SKl are described more
fully in section (7).
3.3 TERMINAL CONNECTOR, SK2
This is a 5 pin 240° DIN connector. Pin l is the
serial data input to the AMr-1 from th e terminal
k eyboard, pin 5 is the data output fr~m the AMT-1
to the terminal display, and pin 3 is the common
return for these pins. The signal levels are
RS232 compatible. Pins 2 and 4 carry control
signals which need not be connected initially
(8.4 and 8.5).
The signal polarit y can be changed by internal
link s ( 8). However, most terir.ir.als ~r smcll
computers will interface directly without alter-
ations. Any CTS or RTS control lines from the
terminal can initially be left unconnected or
strapped into the "unused" state, as appropriai:e
to the terminal in question.
further details about the CTs· and RTS are given
in sections (8) and (11).
.. ::, ~:~. ,.
If your terminal cannot operate at 110 Bauds, remove
the cover of the AMT-1 and cut link 12 to give 75 Baud
operation.
Connect power to the AMT-1. The front panel display
should step through all the combinations of the display.
This verifies that it is working, and it stops with the
ESC LED lit, together with the ARQ, FEC, RTTY and CW LEDs
all dimly lit. A carriage return and linefeej ( newline)
are sent to the terminal on power up. A further check
that the terminal interface is working can be obtained
by typing the letter Q, whereupon the following line
should be displayed:
V:Ol I:???? T;30 B:45 S:20 L:l N:l
The V: number may be differenct on later versions of the
software. The significance of this orint-out is exolained
in (5 .8). - -
Memorise the LED panel display at this point, with the
ESC LED lit and all mode LEDs lit. This is called the
ESCAPE condition, and from it, the AMT-1 can be commanded
to enter any of its three operating modes. It can also be
commanded to alter or set up any of its internal para-
meters. The ESCAPE condition is always reached by entering
an ESCAPE character from the terminal, (except in the by-
pass mode) (5.4). The three modes may be entered by key-
ing the letter A,R or C, for AMTOR, RTTY or CW (morse).
Thus, to change from any mode to, for example, RTTY, enter
ESCAPE followed by R. The ESCAPE character can normally
be sent from the terminal by means of the key labelled ESC .
However, in some computers this key may be used for a
different function, in which case some other way must be
used to send an ESCAPE code to the AMT-1 (11.4).
3.4 TUNING DISPLAY
The AMT-1 has a 16-LED tuning display located in the centre
of the front panel. It is not illuminated in the ESCAPE
condition. To observe how it operates, key the letter A
on the terminal. The tuning display should light. If
there is sufficient background noise from ~he receiver
input, a broad flickering band should be seen. TUne in
an unmodulated carrier in USB mode on the receiver, and
slowly tune the tone across the passband.
At some point the display should stabilise to one or two
LEDs lit at one end, the spot of light moving across the
display to the other end as the tone frequency is tuned
across the passband of the audio filter in the AMT-1-
The display wil finally break up into a broad band of
noise as the tone is tuned out of the filter passband •

Now tune in an FSK signal, and notice how the
signal appears as two dots joined by a dimmer
band of light,as the signal keys from one tone
to the other. Practise tuning such signals to
the point where the two dots are placed
symmetrically either side of the centre line
of the display. Note that the AMT-1 is designed
to receive the 170Hz FSK shift standard, and
it may not always be possible to tune in wider
shift commercial signals without one or the
other (or both) tones remaining outside the
300Hz filter bandwidth of the AMT-1. Ch some
transceivers with variable bandwidth capabil-
ities, it may be advantageous to narrow the
passband of the transceiver so that it just
brackets the AMT-1 passband. Not all trans-
ceivers with a CW filter fitted will operate
in this way if . the position of the BFO is not
suitably placed relative to the CW filter
passband.
3. 5 RTTY OPERATION
To switch to RTTY mode, enter ESCAPE then R.
T he RTTY mode LED will light, and some garbled
characters will appear at the terminal until
an RTTY signal is tuned in. At this point ,
text will become intelligible and the TRAFFIC
and IDLE LEDs will light alternately.
If copy still remains garbled, there could be
several reasons for it: the Baud rate of the
signal could be wrong; the signal may not be
RTTY at all, or it may be transmitting
reverse polarity. To try another Baud-rate,
enter ESCAPE followed by B, followed by the
Baud-rate desired, entered as a two-digit
number (5.2). Common Baud-rates in use are
45, SO and 75. Then enter R to get back to
RTTY mode. If the signal is reverse polarity,
try receiving it on the other sideband .
A
good indication that the signal is reversed,
should it sound to be a hand-keyed signal with
periods of no keying, is that the ERROR LED
will be lit during such periods, indicating
that the stop-bit is of the wrong polarity (9 . 3).
If the signal is not RTTY, it may be an AMTOR
FEC mode signal, in which case try entering
ESCAPE A, as described later.
To transmit an RTTY signal, enter control-A
from the terminal . This is normally done by
holding down the CONTROL key and simultaneously
keying the letter A. If this is not possible
on some personal computers, then a software
routine must be written, or a special function
key programmed to send the ASCII code 01 (11.4).
on entering control-A, the AMT-1 turns the
transmitter on via the PTT line. Check that
the drive level on the transmitter does not
exceed the continuous-carrier level. kijust
RVl in the AMT-1 to achieve the desired level
(7 .3).
Having set the system to transmit an RTTY
carrier, type on the keyboard and the text will
be transmitted over the air, simultaneously
appearing on the terminal display. If the
terminal displays each letter twice, then enter
ESCAPE L ~ and remember in future to do so each
time the terminal is switched on. Also refer
to section (5.6).
To end an RTTY transmission, enter control-D
(ASCII code 04). The AMT-1 will then return
to receive.
3.6 CW OPERATION
To send CW, enter ESCAPE c. The CW LED will
then light. Enter data via the keyboard and
the .l\MT-1 will send it as CW by keying the PTT
line. The PTT line can be shorted to earth to
keep the transmitter on between code elements,
and the AMT-1 will still send perfect CW, since
the tone output is also keyed.
Page 3
The transmitted text is displayed on the terminal as it
is sent. It is possible t.o type faster than the CW send-
ing speed, but remember to use the space bar between words.
To change the sending speed, enter ESCAPE S followed by
the required speed in words-per-minute (5.10) followed by
C to return to CW mode. Do not initially use sending
speeds higher than 50 w.p.m. without consulting section
10.2 regarding setting RV2.
3.7 AMTOR OPERATION
Enter ESCAPE followed by A to enter AMTOR mode. The FEC
LED will light, together with the STBY LED. The tuning
display will also light. In this condition the AMT-1
will do nothing further until an FEC signal is received.
If such a signal is tuned in, at first nothing will happen
until the signal sends a phasing pattern, recognisable as
a characteristic rhythm which is sent from time to time.
It is this which distinguishes an FEC signal from an RTTY
signal to the ear, since when an RTTY station pauses, it
emits an unmodulated carrier. When an idle pattern is
detected by the AMT-1, it will synchronise to it, the FEC
and IDLE LEDs will light, and the tuning display will
change from continuous mode to the "two dot" display, the
line joining the two dots being no longer present (9.2) •
When the distant operator begins to type, the TRAFFIC LED
will light and the . message will be received at the terminal.
At the end of the transmission, the STBY LED will come on
as the distant station sends an "end of transmission" code.
If the signal fades out and no such code is received, the
STBY LED will come back on after some garble has been
printed for a few seconds.
To make an FEC transmission, enter control-a from the
terminal (ASCII code 02). The transmitter will switch on.
Enter the message at the terminal, and end the transmission
by entering control-D (ASCII code 04). It is important to
end with control-D and not ESCAPE, in order to ensure that
the "end of transmission" code is properly sent.
If the characteristic "chirp-chirp" sound of an ARQ
signal is heard, then it should be possible to monitor
it by entering control-F (ASCII code 06). If two
signals are present on the same frequency, · indicated
by interleaved long and short bursts of signal, possibly
at different signal strength, then it will be the one
that is transmitting - sending long bursts - which can
be monitored. If only one signal is heard, sending only
short bursts, then the ARQ-iisten mode will not lock
until that station changes to sending long bursts.
After entering control-F, tune the signal in as · a~curately
as possible and the AMT-l will lock to the signal,
possibly blinking the tuning display a few times at first
if the signal is noisy, but endin~ with the display in
the "two-dot" mode synchronised to the timing of . the
signal. The text being transmitted by the distant station
will be displayed at the terminal. If the signal changes
to receive mode (sending short bursts), the AMT-l will
drop out of sync., the PHASE LED will come on · ~gain and
the tuning display will revert to ' ' t.be continuous mode,
trying to sunchronise to another signal. It will also
do this if it has not received an error-free block for
15 seconds, or if control-F is entered to force the unit
to start synchronising to a new signal.
It is a characteristic of this ARQ-listen mode that, if
the distant signal is idling, false synchronisation is
quite possible. In this case, garble will be displayed
and the ERROR LED may be on even if the signal is clean.
The terminal may well display strings of IIIII, FFFFF,
88888, or %%%%%characters. In this case, enter control-F
again to attempt another sync. Synchronisation will
always be achieved quickly when the signal stops idling.
Tc exit the ARQ-listen mode, simply enter control-D.
The signal being monitored may be making an ARQ phasing
call. If this is the case, · the terminal will display a
repeated 4-letter groµp and the RQ LED will be on
continuously.
This · 4-letter group is . the selective-call code of the
station being called by the station being monitored.
It is normal practice in AMTOR operation for each station
to choose its own unique , -4-letter group, usually chosen
from the letters of · the 'Station callsign. The AMT-1 may
be set to respond to its own unique code by entering
ESCAPE I followed by the 4 letters chosen (5.5),
followed by A to return to AHTOR standby. In this case,
the FEC, ARQ and STBY lamps will light.

If you have entered your own selcal in this way,
and a station calls using this code, then your
station will respond. ·The STBY LED will go out,
the transmitter will be keyed to reply with short
bursts between the · received long bursts of the
calling station, and his message to you will
appear at the terminal. This is one way that
an ARQ contact can be initiated. The other way
is to initiate the ARQ call oneself, using the
selcal code of the station called. To do this:
While the AMT-1 is in the AMTOR mode, enter
control-A (ASCII code 01) followed by the four
letters of the other station's selcal code .
The
PHASE LED will light , and the transmitter
will be keyed with l ong bursts to initiate the
call . When the other station replies , the PHASE
LED will be replaced with the IDLE LED. You may
then type your message to the distant station.
With either method of initiating an ARQ contact,
the direction of sending can be changed in one
of two ways. The normal way is for the sending
station to end his transmission with the
characters +? (no gap between them) . This
signals the other station to commence the change-
over procedure. When this is completed, the two
stations will have changed over from sending long
bursts to short and vice versa. The other method
which must be used with care, is for the receiv-
ing station to enter control-C (ASCII code 03).
To end an ARQ contact, the last station to be
sending should enter control-D (ASCII code 04),
whereupon an "end of contact" code will be sent,
switching both stations back to STBY. Refer to
(10. 2) if you have problems with ARQ contacts .
If propagation between the two stations is poor,
the contact may sometimes be held up by repeat
sequences ,' i~dicate d by either the ERROR or RQ
LED being . ~ it. In this case, the terminal data
output will pause whilst the repeats are in
progress. this occurs at the receiving end,
and also during . "local copy• at the sendinq end.
If the ERROR or RQ LEDs are on continuously for
15 seconds or more, then a PHASE operation will
take place, during which the original calling
station will repeat the call and the originally
called station will cease keying and attempt to
re-synchronise. 1'b intervention by either
operator is needed during this operation.
Typing may continue at either end, provided the
internal buffer stores do not overflow (4.2).
If, in the PHASE condition, contact is not
re-established within 30 seconds, then the
station will revert to STBY. This 30 seconds
time-out can be changed to any value between
one and 100 seconds by entering ESCAPE T follow-
ed by the required time-out figure (5.11).
4. OPERATING HINTS
4.1 In RTTY and AMTOR modes, transmission is by
means of a code with 32 different combinations.
Two of these are used to switch ensuing text
between one set of 30 letter characters and
another set of 30 figures and punctuation marks.
These "lettershift" and "figureshift" characters
are automatically generated by the AMT-1 in the
translation from ASCII code. In most cases the
user need not be aware of the operation.
However, it sometimes happens that the received
text gets in the wrong character set by mistake.
If the received text appears in figure-shift
erroneously, enter a DELETE character from the
terminal (ASCII code 127, or HEX 7F). This will
force the following received text back to letter-
shift.
The AMT-1 has an automatic system for sending an
extra shift character after either a carriage
return, linefeed, or NULL character, which
ensures that a distant station will always start
a new line in the correct shift. Since the rec-
eived shift will be unknown at t he start of a
transmission, therefore, it is always good
practice to start each transmission with a
carriage return and a line feed.
Page 4
This al so has the effect of ensuring that both the
sending and receiving print-positions are synchronised
and ensures that the distant receiving station's first
line does not overrun the end of the line.
The AMT-1 also has an automatic system to generate a
carriage return and linefeed if a space character is
entered after the 60th character in a line. This
ensures that overprinting can not occur at the receiv-
ing end, particularly if the user is typing faster than
the terminal is echoing the text and is not aware of
approaching the end of a line. This facility can be
disabled by entering ESCAPE N ~ (5.7).
During RTTY and ARQ contacts , it is possible to type
into the AMl'-1 even wh il st receiving. Any text so
entered will be held in the internal buffer, and will
the n be transmitted as fast as possible when the
terminal unit bas changed to transmit. This type-
ahead facility is not available on FEC mode, although,
if text is entered faster than six character per second,
it will build up in the buffer, as it will in CW mode.
Since, when transmitting in FEC mode, distant stations
can only synchronise when the signal is idling, each
transmission must start with a period of idles. The
AMT-1 does this automatically for a short period, but
if a longer period would help the distant station to
tune in, then, after entering control-B, simply leave
a suitable pause before commencing typing. The practice
common in RTTY of sending a line of RYRYRYRY at the start
of a transmission to allow the distant station to tune in
is not helpful on FEC mode.
4.2 The internal t ransmit buffer will hold 960 characters,
allowing a useful amount of text to be typed in advance
if required. If the buffer fills , any more text entered ·
will be lost. It is possible to prevent this if the
user's terminal is an intelligent computer, by using the
RTS output from SK2 pin 4 to inform the computer that
the buffer is full. See section (8.4 and 11.l).
To cancel the buffer contents completely, enter contrcl-X
(ASCII code 24, or HEX 18).
Note that if there is still some text waiting in the
buffer when control-D is entered to end the transmission
(in RTTY or FEC) or end the contact (in ARQ mode), then
the remaining text will be transmitted before closedown.
If control-X is entered after control-D and before the
closedown has ta.ken place, then the closedown is cancelled.
The transmission will then idle w hen the buffer has emptied.
In the previous section, it was mentioned that the use of
control-C to "break-in" to the other station's transmiss-
ion during and ARQ contact, must be u sed with care . The
reason is that any subsequent +? sent after the break will
probably leave the remainder of the distant station's
broken transmission in figureshift. The DELETE key will
have to be pressed quickly to correct this. It can also
be confusing to the distant operator if he is interrupted
in the middle of a transmission. If the distant station
interrupts you in this way, and you wish to respond to
the interruption, then enter control-X to clear the buffer
and enter a carriage return linefeed to set the correct
shift.
The normal method of establishing contacts on RTTY is to
put out a CQ call and then listen for a reply, or to call
a station after hearing him end a contact. Ch AMTOR, it
is normal practice to make CQ calls in FEC mode, announc-
ing your own selcal code during the call. At the end of
your call, a distant station can then call you back in
either FEC or ARQ mode, provided of course, that you have
previously entered your selcal code using the ESCAPE I
procedure (6.5). Another way to initiate an ARQ contact
is to call a station directly in ARQ mode, perhaps as he
is ending a contact. You must, of course, know his selcal
to do this. It is also common for AMTOR stations to
maintain a listening watch on a common frequency, in which
case a selcal transmitted on the frequency will quickly
establish if the station is available.
When making an ARQ call using a transceiver, it can
happen that the replying station comes back slightly off -
tune, indicated by an off-centre tuning display. rt is
tempting to correct this error by adjustment of the main
tuning dial. This temptation should be resisted, as it
will result in the transmitter frequency changing as well,
and this will probably result in the distant station
having to retune at his end.

This can result in an endless series of retune
operations at · both ends. The rule, therefore, is
for the calling station to leave his main tuning
control untouched, and to retune any offset with
the receiver clarifier control (RIT). The called
station should leave his RIT in the central pos-
ition, and use the main tuning to ensure his
tuning display remains central throughout the
contact. A different technique may be needed if,
for example, one station is crystal-controlled.
It is ev en possible to adjust the transmitter
frequency independently of the receiver, whilst
w atching the RQ LED. Set th e fr equenc y to the
midp oint of th e range outside of which th e RQ LED
comes on as a result of the di stant station
req" ~ esting a repeat wh en y our signa l is off
tune in his receiver! A similar operation can be
used to optimise the transmitter power level.
The power output of the transmitter can be reduc-
ed progressively during an ARQ contact to the
point just before the RQ LED starts to come on.
Remember that no text will be l ost if the power
is reduced too far for a moment or two, It is
even possible to make a pre-arranged change of
frequency or band. With care, this can be
achieved in the middle of a contact without
l osing any text. The calling station must be
the first to change frequency in this way, with
the called station following, so that the calling
station begins to send the phasing pattern on the
new frequency if the change tak es longer than 15
seconds.
4.3 There are some inherent operating limitations
associated with the us e of different transmission
speeds at each end of the AMr-1. For example, if
an RTTY signal is received at 100 Bauds, and is
sending traffic at fu ll speed with no gaps,
characters will be entering the unit at a rate of
13.33 per sec. If the terminal is operating in
110 Baud ASCII, then characters will be sent to
the terminal at a rate of 10 per second.
5.
Text will buil d up in the internal 64 ch aracter
buffer and this may eventually fill. If it does,
some text will be lost. Although the unit is
capable of copying RTTY at a data rate of 100
Bauds, it cannot handle a character rate faster
than 10 c.p.s. when operating with a terminal at
110 Bauds, and no faster than 6.66 c.p.s. when
operating at 75 Bauds.
There is no restriction on receive speeds when
operating in AMTOR mo de, as the maximum character
rate receivable on AM TOR is 6.66 c.p.s . There
m ay, however, be a problem when transmitting, as
text entered at 110 Bauds from the terminal may
build up in the transmit buffer when operating
in AMTOR mode or in RTTY mode at Baudrates lower
than 75. The transmit buffer is much larger
(960 characters) and the RTS handshake line is
available to extend this when required in computer
applications (11.l) • Ch slow speed CW, text will
normally build up in the buffer anyway, and since
CW is sent at a non-uniform character rate, it is
an advantage that some text is held in the buffer
to keep the letter spacing correct. If sending
at high cw speeds, especially from a 75 Baud
terminal, the buffer may always remain empty, and
this will give rise to uneven letter spacing in
the output morse code.
ESCAPE CODES
From
previous sections, it should be clear that
other than changing from one mode to another by
using t he ESCAPE key, further functions may also
be carried out. These will now be described in
detail. These codes are normally preceeded by
ESCAPE, but if the AMT-1 is already in the ESCAPE
condition, as shown by the ESC LED plus all four
mode LEDs, then another ESC code is not needed.
Page 5
5.1 ESCAPE A
This code enters the AMTOR standby mode from . whence
FEC signals may be received. ARQ can also be received
if the selcal code has been entered. FEC or ARQ
transmissions can be made, or ARQ signals may be monit-
ored, by using control-B, control-A, or control-F, as
described above.
5.2 ESCAPE B
This mode enables the user to set the Baudrate at which
the AMT-1 is t o operate when in the RTTY m ode. After
entering B, follow it with a two-digit number, indicating
the desired Baudrate . Although th e common Baudrates are
45 , 50 and 75, th e AMT-1 will accept any figure between
01 and 99. l'Cte that if Baudrates below 10 are required,
the leading zero must be entered. If 00 is entered, the
unit will be set to 100 Bauds. Both transmit and receive
are set to the same Baudrate. If a character other than
a number in the 0 - 9 range is entered by mistake, the
terminal will print a questionmark and the AMT-1 will
return direct to the ESCAPE mode. While the Baudrate is
being entered, the ESC and RTTY LEDs will be lit. When
the second digit has been entered, the AMT-1 will return
to the ESCAPE condition.
5.3 ESCAPE C
This code enters the CW mode, as previously described.
5.4 ESCAPE D
This code enters the "direct" or bypass mode , in which
the microprocessor is bypassed and serial data from the
terminal is passed direct to the output frequency-shift
generator. Serial data demodulated from incoming
received audio is fed directly v ia the serial output
to the terminal. In this mode, ASCII code cap. thus be
transmitted and received (simultaneously, if required).
The Baudrate is determined by the terminal , and indeed,
any code or speed can be transmitted through the system
under these conditions, subject to the limitations of the
receive filter, which limits the top speed to about 120
Bauds. l'Cte that in this mode the PTT line is c ontinuousl y
enabled. This is necessary in order to keep the tone
generator switched on. The PTT line must be externally
d isconnected from the transceiver to allow it to pass
received signals. The AMT-1 will not respond to any
ESCAPE code in this mode . An ESCAPE code wi ll be trans-
mitted directly over the radio. The only way to "escape"
from this mode is to switch the power suppl~· off and then
on again.
5.5 ESCAPE I
This code enables the user to set the selective call
" ident" of the unit. This is the four-letter group to
which t he unit will respond in ARQ mode. If the ESCAPE I
function has not been used since the unit was switched on,
then the unit will not respond to ! \NY ARQ call, but o nl y
to FEC transmissions. To set th e ident, enter ESCAPE I
followed by the required four-letter group. Only the
l etters A - z are accepted. If any other character is
entered, the terminal will display a questionmark and
revert to the ESCAPE condition. Whilst the ident is
being entered, both ESC and ARQ LEDs will be lit .
When the fourth letter has been entered, the unit will
revert to the ESCAPE condition.
5.6 ESCAPE L
This code turns on or off the "echo" facility, whereby
i nput from the terminal is sent back to the terminal to
appear on the display. This is the normal way in which
it will be used, with the terminal effectively working
as a separate keyboard and display. If _ the terminal ha s
its own "echo" or "local copy" facility, then this should
be disabled. In the event that this cannot be done, then
the echo facility of the AMT-1 will have to be disabled.
This is achie v ed by entering a zero after the L. The
lack cf t~e AMT-1 echo facility is a distinct disadvantage,
especially in ARQ mode ( w here the presence of the echo
indicates when each character h as been transmitted and
accepted by the receiving station.

ESCAPE L 1 is used to turn the echo on again.
On switch-on, the echo is enabled.
5.7 ESCAPE N
This code turns the automatic-newline facility
on or off. It i s enabled at switch-on and will
automatical ly ensure that both a carriage return
and a line feed are inserted into the text in
substitution for any space which occurs after
the 60th character position in any l ine. This
ensures that no line is too lo ng for the distant
station's printer. In cw m ode, carriage return
and linefeed codes are not transmitted, but
nevertheless the auto n ewline function serves
to format the echoed text on the terminal into
neat lines.. When it is desired to use a different
linelength, the auto-newline function may be
disabled with ESCAPE N ~ and enabled with
ESCAPE N 1.
5.8 ESCAPE Q
!i.
This code causes the AMl'-1 to output to the
terminal values of all of the parameters that
have been programmed via other ESCAPE functions.
This explains the print out wh en Q is entered to
test that the AMI'-1 is w orking . The number
printed after the V: is the version number of
the software. When the unit is switched on,
the ident will be shown as I:????, to indicate
that no ident has been set. The unit will not
respond to any ARQ call. The AMTOR timeout is
set to T: 30, the Baudrate to B:45, the CW speed
is S:20, and the L: and N: are both l at switch-
on. N ote that all these parameters are retained
even though the mode may be changed. It is not
necessary to " re-enter the ident before entering
AHTOR mode each time.
5.9 ESCAPE R
This code selects RTTY mode. on selection, the
AMT-1 will receive RTTY. Control-A will change
it to transmit, and control-D returns it to
recei v e, as previously described.
5 •10 ESCAPE S
This code allows the user to set the word-per-
minute speed that will be used in cw mode. one
should enter a two-digit number after the S, in
a similar fashion to that used for Baudrate.
Use a leading zero for speeds less than 10 w.p.m.
Entering 00 will set 100 w.p.m., and if a
character other than a number is entered, a
questionmark will be printed.
5. 11 ESCAPE T
6.
This enables the user to set the time-out in the
ARQ phasing condition, i.e. the length of time
in seconds during which the unit will keep try-
ing to resynchronise with the other station be-
fore giving up and returning to STBY. Again,
a two-digit number between Ol and 99 can be
entered, with 00 giving 100 seconds :
CONTROL CODES
A part from ESCAPE sequences, other functions
executed by the AMT-1 are selected by ASCII
control codes, usually entered from the terminal
by depressing the CONTROL key and simultaneously
k eying a letter. Not all control codes have the
same meaning in different modes, nor are all
active in all modes.
6.1 CONTROL-A
In RTTY mode, this code forces the AMr-1 from
receive to transmit. In AMTOR mode, followed
by four letters to form the outgoing selcal code,
it initiates an ARQ call. If a character other
Page 6
6.2
than a letter (A - Z) is entered as any of these four,
the unit will print a questionmark and then revert to
AMI'OR STBY. Control-A has no effect in CW mode.
CONTROL-B
In RTTY mode this code has the same effect as control-
A. In AMrOR mode, it will initiate an FEC transmission.
In cw mode it has no effect.
6•3 CONTROL-C
This code has the same effect as control-D in RTTY
mode. During an ARQ contact, it can cause a "break-
in" if the distant station is sending. Control-C has
no effect in other modes.
6.4 CONTROL-D
In RTTY, control-D switches from transmit to receive.
In AMTOR FEC transmit, it causes an "end of transmiss-
ion" code to be sent, followed by switching off the
transmitter and reverting to STBY. During ARQ contacts,
control-0 will cause the contact to be terminated,
switching both stations to STBY. This works only when
the station that entered control-D is in send mode and
has finished sending any text that may be in the buffer.
If control-D is entered whilst the station is in receive,
then closedown will be delayed until the station switches
to send. In the ARQ-listen mode, control-D terminates
the listening mode and returns the unit to STBY.
Control-D has no effect in cw mode.
6 •5 CONTROL-E
This code is a special one and causes a specific non-
ASCII code to be sent from the AMl'-1 to the terminal.
This code can be interpreted by a computer, the details
of which are described in section (ll.3). Ch most simple
terminals, this "status" code may or may not print as a
character of some sort. It might be interpreted as a
control character by the terminal, and for this reason
control-E should be used with care.
6.6 CONTROL-F
This is only valid in AMl'OR mode, where it will initiate
the ARQ-listen mode.
6.7 CONTROL-G
This is not strictly a control code, but will cause a
BELL character to be transmitted to the distant station.
The echo back to the terminal will be an asterisk.
This ensures that if the terminal itself is configured
to respond to a control-G by issuing an audible alarm,
it will not do so if an alarm code is transmitted.
If a BELL code is received over the radio, the AMT-1
will send a control-G to the terminal, however.
6.8 CONTROL-X
In RTTY, CW, ARQ and FEC transmit modes, control-X will
cancel any text which may not yet have been sent from
the buffer • . In addition, if control-D had previously
been entered ~ o signal the end of the transmission or
contact, control-X will effectively cancel control-D.
6.9 DELETE
7.
In RTTY and AMTOR modes, this has the effect of forcing
any subsequently received text into the "lettershift"
character mode. It can be used to correct '1IlY received
signal which has switched into figureshift in error.
Carriage retur n , linefeed and NULL control characters
are treated as text and passed to the transmitter.
They also have the effect of causing t he next non-
control character to be preceeded by the appropriate
lettershift or figureshift.
SKl:
TRANSCEIVER CONNECTOR
7.1 Pin 2 is the common earth return for the other signals
carried by this socket. It is also strapped to the
metal chassis of the AMT-1 to ensure good immunity
from external RF fields. The screens of the leads
to pins l and 3 should be connected to this pin.

Page 7
7. 2
Pin l is the audio input from the receiver. The
input impedence is lOOK Ohms and the audio level
should be between SQn V. and l V. rms.
This signal may be derived from the external loud-
speaker socket of the transceiver, but it is
better if the audio can be taken from a point ahead
of the gain (volume) control such that the speaker
volume can be varied (or turned off) without affect-
ing the audio level to the AMT-1. An audio output
is often available from the accessory socket or
phone-patch socket or it can simply be wired to a
spare pin on the MIKE socket.
'lb ch eck t hat the audio level is within the correct
range, tune in an unmodulated carrier that can be
varied in level. The position of the tuning dis-
play should not vary as the audio level is varied
slightly up or down.
7.3 Pin 3 is the audio output from the AMT-1 to the
transceiver . This is a sinewave and can be varied
between zero and l v. rms by means of the internal
preset, RVl. The tone is keyed on and off by the
microprocessor, turning on a little after the PTT
line does, such that there is no drive to the
transmitter until the changeover to transmit is
completed. This ensures that no key-clicks are
radiated. Pin 3 can be connected to an auxiliary
audio input on the transceiver if such an input
is available . ~rmally it will be taken to the
MIKE input. If the audio level from the AMT-1 is
too high, fit a resistor in series with the MIKE
input connection at the transceiver end of the
lead. This will drop the audio level to that
normally expected from a microphone.
It should be possible to leave the MIXE gain
control in its normal position. Choose a series
resistor such that RVl can be set to give the
correct transmitter drive level with its slider
somewhere near the middle. It is important not
to overdrive the MIKE input of the transceiver,
or spurious emissions can be produced on either
side of the wanted signal, even if the transmitter
output stage is not overdriven.
7.4 Pin 5 is the PTT line connection. This is driven
from the AMT-1 by an open collector transistor
which connects the line to ground when the AMT-1
enters transmit mode. The PTT line must be
positi ve with respect to earth at the transceiver ·
when
in receive condition. This is true of all
popular transceivers. A simple connection can
therefore be made between the AMT-1 and the PTT
l ine which will normally be available on the MIKE
socket. In the event that . the PTT input on the
transceiver is not of the "earth-to transmit"
type, then a small relay should be connected
between the AMT-1 PTT output and the + 12 V.
supply. The contacts can be connected to the
transceiver .
Pins 4, 6 and 7 are not connected.
8. SK2: TERMINAL CONNECTOR
8.1 Pin 3 of SK2 is the common earth return '" for the
other pins on the socket. It is also connected
to the A.'fl'-1 chassis.
8.2 Pin l is the serial input from the terminal to
the AMI'-1. A negative voltage on this pin corres-
ponds to the stop-polarity, and a positive voltage
to the start polarity. The terminal should output
a negative voltage to the AMT-1 on this pin when
in idle condition. If the polarity needs to be
reversed, the internal link LJ.O in the AMI'-1 can
be cut. The data into the AMT-1 must be ASCII
code with one start bit, 8-bit data bits, and
either one or two stop bits. The eighth data bit
(sometimes called the parity bit) is ignored by
the AMT-1, and can be either zero, one, odd, or
even parity. The data rate accepted by the AMT-1
is either 75 or 110 Bauds, selected by internal
DIL switch SW3 (10.5).
8.3 Pin 5 is the ASCII output from the AMI'-1 to the terminal.
The logic l evels and data format are as per the input on
pin l. The AMT-1 outputs are zero (start pol'arity) in
the parity bit with the exception of the "status"
character output. This is sent when the AMr-1 responds
to a control-E character from the terminal (11.3).
In this case the parity bit is one. The polarity of the
output signal can be inverted by cutting LKS.
8.4 Pin 4 is the RTS (Request To send) output from the AMT-1
which can safely be ignored in most applications.
!bwever, its purpose is to inform the terminal, or compu-
ter, when the AMT-1 can or cannot accept text for trans-
mission. For example, if the internal 960 character
buffer fills during entry of text from the terminal, then
RTS changes. The cemputer should respond by stopping the
flow of data until the AMT-1 signals that there is a space
in the buffer. This line also indicates that the AMT-1
cannot accept data when it is not in a transmit mode, such
as FEC-receive or ARQ-listen, or during an ARQ call
before the distant station has replied. A positive volt-
age on this line indicates that text can be accepted, and
a negative voltage indicates that it cannot. !bte that
the AMT-1 will still accept control characters even if
this line is negative. The polarity of this signal can
be inverted by cutting link LK4 (11.l) •
8.5 Pin 2 is the CTS (Clear 'lb Send) input to the AMT-1.
For most applications, this pin can be left disconnected.
It serves a similar purpose to that of pin 4, but in the
opposite direction. It can stop text from being sent out
by the AMT-1, e.g. when the computer is temporarily busy
with another task, such as storing a block of text on
disk or cassette. During this time any data from the
AMT-1 might be missed. If this pin is taken negative,
then any received text will be held in a temporary 64-
character buffer within the AMT-1. It will be released
when CTS is taken positive (or left open) • • The polarity
of this signal can be reversed by fitting a iink in LK6
position. If this is done and CTS is left open, then the
AMI'-1 will not permit any data output. In this case, CTS
must be held negative if it is not used. see section (11.2).
9. FRONT PANEL DISPLAY LED'S
There are three displays on the front panel. The right-
hand one,comprising four red LEDs, indicates which of the
principal modes the AMT-1 is in. The centre display, com-
prising green LEDs, is a tuning display. It gives an
analogue indication of the frequency of the received tones.
The left-hand display indicates the status of the unit
within each mode. The significance of each LED · is described
below:-
9.1 MODE DISPLAY
ARQ is lit when the AMr-1 is in AMTOR standby mode and is
ready to receive either FEC or ARQ calls, or if it is in
ARQ conta ct or making an ARQ call.
FEC is lit if the AMI'-1 is either receiving or transmitting
an FEC signal.
RTTY is lit when the AMT-1 is in RTTY mode, either transmit
or receive.
CW is lit in the CW mode.
9.2 TUNING DISPLAY
The tuning display is turned on only when the AMT-1 is i.~
receive. A high-frequency tone will give a spot on the ·
left side of the display, and a low frequency tone on the
right side. In RTTY receive, the display will be lit
continuously. A signal will show as a dot which should
flicker rapidly between the left and right-hand side of
the display. In FEC receive, the display changes to the
"two-dot" mode, where the display is only gated on at the
exact centre of each data bit. Thus the display will not
show the dot as it traverses from one side of the display
to the other, but only as two separated dots - one on each
side.