MFJ MFJ-1224 User manual

MFJ RTTY/CW
COMPUTER INTERFACE
MODEL MFJ-1224
OWNER'S MANUAL

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MFJ-1224 RTTY/CW COMPUTER INTERFACE
Thank you for purchasing the MFJ-1224 Interface. The MFJ-1224 will allow you to transmit
an receive RTTY an CW when use with your transceiver. During reception, the MFJ-1224 con-
verts the CW or AFSK tones from your receiver into computer compatible TTL level signals. The
computer then translates these signals into the represente alpha-numeric characters an isplays
them on the screen. In the Transmit Mo e, the computer generates the TTL signals which are con-
verte by the Interface into AFSK tones for RTTY or into CW keying for CW transmission.
NOTE: The interpretation of the TTL signals requires a specialize HAM program which is
not provi e with the interface. This allows you to select a program which is compatible with your
computer an which has the features you want.
When unpacking, make sure that all of these items are inclu e : (1) INTERFACE, (1) FOUR
PIN MIC PLUG, (1) RCA CABLE, (1) FIVE PIN PLUG, (1) MIC CABLE WITH FIVE PIN PLUG AT-
TACHED an (1) OWNERS MANUAL. THE 12-VDC AC-ADAPTER IS OPTIONAL.
FRONT PANEL
The front panel controls an in icators consist of five push button switches an four LEDs. From
left to right, they are as follows:
ON/OFF This switch controls the power to the interface.
POWER LED This in icator is lit when the power in on.
PHASE LOCK LED This in icator is use with the DATA in icator to ai in tuning the receiver. It
in icates when the interface is locke onto an RTTY signal. It flashes with
the Morse Co e tone for CW reception.
DATA LED This in icator is use with the PHASE LOCK in icator to ai in tuning the re-
ceiver. It flashes on an off with RTTY shift an also flashes with the Morse
Co e tone for CW reception.
CW Transmit LED This in icator is activate by the CW keying circuit. It flashes uring CW
transmission.
RTTY/CW This switch selects either the RTTY or CW mo e of operation.
Shift The next two switches control the shift for RTTY:
In this position the interface is set for a 850 Hz au io shift
In this position the interface is set for a 170 Hz au io shift
In this position the interface is set for a 425 Hz shift an 170 Hz
sen ing shift
In this position the interface is set for a 425 Hz shift an 850 Hz
shift
NORMAL/REVERSE This switch inverts the emo ulate RTTY signal being sent to the computer.

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BACK PANEL
The MFJ-1224 provi es inputs an outputs to allow interfacing to nearly any possible com-
bination of computer an transceiver. The back panel iagram below shows all the interface con-
nections an the paragraphs below escribe their uses. Only a few of the available connections will
be use for any given application; however, the available of a variety of signals greatly enhances
the versatility of the interface.
LOOP OUT The loop-out jack provi es the groun return to rive loop type teletypes.
The user must connect the negative supply voltage to the sleeve. The center
pin is a continuation of the negative supply. The loop out merely acts as a
spst switch switching the loop current on an off.
DIRECT KEYING This output keys rigs requiring irect keying(most rigs with soli state finals)
GRID BLOCK KEYING This output keys rigs requiring gri block keying (most rigs with tube finals)
KEY IN This input jack allows you to externally key the transmitter with your own
electronic keyer or keyboar .
DEMOD OUT The emo ulate output provi es a TTL level signal which correspon s to
the incoming RTTY or CW signal. This output is high on RTTY mark an low
on RTTY space. It is also low for CW tone.
The next connector is a five pin jack, labele K-connector because it is specifically esigne
for use with KANTRONICS software. From left to right the pins are as follows:
DEMOD This pin pro uces the same output as the DEMOD out jack.
GROUND This pin provi es the groun connections between the interface an the
computer.
CW KEY This input pin allows the computer to key the transmitter through the inter-
face. A low on this pin causes the interface to key the transmitter.
RTTY This input controls the AFSK for RTTY transmission. It works in conjunction
with CW ID signals an to operate the push-to-talk switch. This will be cov-
ere in etail later.
CW ID This line controls the au io tone for CW i entification. It works in conjunc-
tion with the RTTY line to pro uce RTTY an CW ID signals an operate the
push-to-talk switch. This will be covere in etail later.

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Next is a eight pin general purpose connector which allows you to a apt the interface to al-
most any computer an software. An internal DIP switch allows the inputs an outputs to be in-
verte if necessary to correspon to the requirements of your computer. From left to right, the
pins are as follows:
RTTY DEMOD This output is a TTL version of a receive RTTY signal.
GROUND This pin provi es the groun connection between the interface an the com-
puter.
CW ID This input pin controls the shift for CW ID transmission.
RTTY This input pin controls the mark an space shift for RTTY transmission.
PTT This input controls the push-to-talk switch of the transmitter.
CW KEY This input controls the transmitter keying circuit.
+5 VDC This input provi es a 5 volt supply for external circuitry such as an RS-232
converter.
Next is a five-pin jack which is use for the microphone connection. From left to right, the
pins are as follows:
PTT OUT This pin is connecte to the high si e of the push-to-talk line. It is shorte to
groun to key the microphone.
PTT GROUND This pin is connecte to the groun si e of the push-to-talk line.
AFSK SHIELD This pin is connecte to the groun for shiel si e of the AFSK line.
AFSK OUT This line carries the au io signal for AFSK RTTY to the microphone input.
FSK OUT This line provi es FSK signal for keying FSK rigs.
AUDIO IN The au io input jack shoul be connecte to the external speaker jack or
hea phone jack of your receiver with a shiel e au io cable. The interface
en of the cable requires an RCA type plug.
SPEAKER OUT The speaker output jack may be connecte to a speaker using shiel e
au io cable. The interface en of the cable requires an RCA type plug.
12 VDC The power jack requires 12 VDC from a 2.5 mm subminiature plug with the
tip positive an the sleeve groun .

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PRELIMINARY CONNECTIONS
Input an output signals must be TTL level (+5 VDC an groun ). Inputs are RTTY an CW
KEY (RTTY an CW on general purpose connector). There is also a separate CW ID input for i enti-
fying in MORSE while operating RTTY. Outputs are DEMOD (RTTY DEMOD an CW DEMOD on the
GENERAL PURPOSE CONNECTOR) an DIRECT an GRID BLOCK. Connections epen on the type
computer an transceiver use . Either the GENERAL CONNECTOR or the K-CONNECTOR will be
connecte to the computer.
CONNECTIONS
FOR CW For transmission an reception of CW, the following connections are necessary.
1.) A 12 VDC power supply to the POWER jack of the interface.
2.) A shiel e au io cable from the external speaker jack of the transceiver to the AUDIO in jack
of the interface.
3.) If esire , a speaker may be connecte to the SPEAKER out jack of interface.
4.) If the interface is to be use to key the transmitter by han , the key shoul be connecte to
the KEY in jack.
5.) The control cable from the computer to the interface.
6.) A cable from one of the KEY out jacks of the interface to the key in jack of the transceiver. If
you are not sure whether your transceiver requires GRID BLOCK or DIRECT KEYING, try one
an then the other to see which one works. No amage will be one if the wrong one is se-
lecte .
FOR RTTY/ASCII For transmission an reception of RTTY or ASCII signals the following con-
nections are nee e :
1.) A 12 VDC power supply to the POWER jack of the interface.
2.) A shiel e au io cable from the external speaker jack of the transceiver to the AUDIO in jack
of the interface.
3.) If esire , a speaker may be connecte to the SPEAKER out jack of the interface.
4.) The microphone/PTT cable to the transmitter. This cable is supplie with the proper push on
the connector on one en an with the other en unwire . This allows the cable to be con-
necte properly for various types of transmitters. For transmitters that have three wire
microphone connectors, only three of the microphone cable are nee e . AFSK shiel shoul be
connecte to groun , PTT shoul be connecte to PTT OUT an AFSK shoul be connecte to
the AUDIO INPUT. The FSK OUT is not connecte when use for AFSK operation.
Consult the owner's manual for your transceiver to etermine the proper connection of the
MICROPHONE JACK. The white wire is the au io line, the re wire is the PTT line, the black
wire is the PTT groun line, the bare (shiel ) wire is the au io groun an the green
wire is the FSK line.
5.) The control cable from the computer to the interface.
6.) If the interface is to rive a TTY current loop, the TTY shoul be connecte to the LOOP out
jack. The sleeve is the negative si e of your supply. The LOOP OUT pin is usually connecte to
the negative si e of your selector magnets.

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INTERNAL CONTROLS
Caution: Improper a justments of the internal controls will prevent the interface from functioning.
The MFJ-1224 has several internal controls an a justments, as shown in the iagram an e-
scribe below. The layout is shown in FIGURE 4.
AUDIO OUT GAIN This controls the level of the au io for AFSK output. It is preset at the fac-
tory to a reasonable level for most transmitters. Some a justments may be require if your trans-
mitter requires a higher or lower setting. The best results usually occur with high level from
the interface an a low mic gain setting on the transmitter.
INPUT LEVEL It is very important that the input is set to the proper level for use with your
rig. First tune the ra io until no signal is hear (static only), then set the volume slightly lou er
than your normal listening level. Turn the input level pot to the point where the static
oes not cause any flickering of either the PHASE LOCK LED or the DATA LED.
OPERATION
SETTING UP THE MFJ-1224 for CW
Computer Operation:
Enter the program into your computer. Follow the irections provi e with your software. If
using the Kantronics software, it will ask you to "PRESS K" for Kantronics interface or "T" for user
terminal unit. You must press "K". If you press "T", your transmitte RTTY will be inverte .
Teletypewriter Operation:
If your ra io teletype provi es TTL voltages for input an output, you can hook it irectly to
the MFJ-1224. If not, you will have to use the loop supply circuit an a current loop to the TTL in-
terfaces. (SEE CQ, November 1983, page 49.)
CW OPERATION:
The MFJ-1224 uses it's Active RTTY filter to give selectivity for Morse signals an is tune to
2125 Hz., one of the RTTY "High Tones"; consi erably higher than the usual 900 – 1000 Hz. In or-
er to center your CW signal to the CW frequency of the station you are working, some a just-
ment to your receiver's controls will be necessary.

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TOP VIEW
FIGURE 3
MFJ-1224 CONTROL SETTING
1. Set the front panel switches on the MFJ-1224 as shown in Figure 3.
2. Tune the receiver until you hear only noise.
3. Turn the au io gain up to maximum.
4. Re uce RF gain for a comfortable listening level.
5. Remove the cover of the MFJ-1224.
6. A just the internal input level trimpot (next to the NORM/REV switch) until the PHASE LOCK
LED an the DATA LED o not flicker with the au io input (noise). (SEE Figure 4.)
Transceiver Settings:
SET: Mo e to CW
X-tal to ON
RIT to OFF
IF-Shift to ZERO (Center)
Tune in the X-tal Cal as a Morse LO-Tone (900 – 1000 Hz).
Turn ON the RIT.
Please o not touch the VFO.
Transceivers without CW Filters:
A just RIT for a higher pitch until the MFJ-1224's PHASE LOCK an DATA LEDs light. Finish
the setting un er the hea ing "FINISH".
Transceivers with CW Filters, RIT an IF-SHIFT:
A just RIT for a higher pitch. Note that as the pitch goes up, the signal begins to move out
of the PASSBAND of the CW FILTER (S-Meter starts to fall). Using IF-SHIFT, move the CW FILTER
PASSBAND, keeping it over the signal (S-Meter UPSCALE). Continue raising the pitch with the two
controls also watching the MFJ-1224's PHASE LOCK an DATA LEDs. When the LEDs come on,
carefully a just the RIT to center the signal in the PASSBAND of the MFJ RTTY FILTER. Carefully
a just the IF-SHIFT to center the signal in the PASSBAND of the transceivers CW FILTER. Finish
un er the hea ing "FINISH".

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Transceivers with CW Filters, No IF-Shift:
Switch to USB an a just the RIT, as above, for "Transceivers without CW Filters." You will
receive an tune stations in the USB MODE, transmit in the CW MODE. Finish the setting un er the
hea ing "FINISH".
Transceivers with CW Filters, No RIT:
Remove the CW FILTER so that the MORSE may be copie via the SSB FILTER. The MFJ-
1224 will provi e the selectivity as nee e for computer work. Procee as per "Transceivers with-
out CW Filters".
Finish:
Log the settings of the CONTROL(s) for future reference. Turn the X-TAL CAL OFF.
With the controls of the MFJ-1224 set for CW, all Morse Tuning will be ma e with the VFO.
Your transmit signal will appear on the frequency to which the other station is listening. If the
transceiver has a igital isplay frequency counter, then your actual transmit frequency will be is-
playe DURING TRANSMIT. Please resist any temptation to a just the RIT an IF-SHIFT from their
"preset" positions.
CW TUNING
1. Tune the receiver to start at a low pitche tone, then progressively tune for a higher pitch. As
you tune higher in pitch, the following occurs:
A. The PHASE LOCK LED blinks On an Off with the co e.
B. Both PHASE LOCK an DATA LEDs blink On an Off simultaneously.
C. Both LEDs remain Off.
* IMPORTANT *
The on y correct tuning occurs at 'B' above when both the PHASE LOCK and the DATA
LEDs b ink ON and OFF simu taneous y with the code.
When the PHASE LOCK an DATA LEDs are blinking simultaneously with the co e an you
on't see noise spikes triggering the LEDs, the DEMOD output will be low (0 VDC) for no tone
an high (+5 VDC) for a tone.
2. Look at your TV screen. The Morse shoul be followe correctly.
NOTE: It may take several lines for the computer to start receiving the Morse correctly.

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SETTING UP THE MFJ-1224 FOR RTTY
Tuning RTTY signals is much easier than tuning CW because reception is not affecte so
much by noise. Since the signal is always present, noise oesn't have a chance to affect the recep-
tion as in CW where the signal is absent for so much time. If a justment for CW has alrea y been
ma e, then a justment for RTTY will probably not be necessary. If the input level trimpot has not
been a juste , follow the proce ure for CW, steps 1 through 6.
* CORRECT TUNING *
The on y correct tuning condition on RTTY is when the PHASE LOCK LED is ON continu-
ous y and the DATA LED is b inking on and off the most pronounced.
1. Set the switches on the MFJ-1224 for RTTY, 170 Hz shift, an NORMAL (SEE Fig. 3A).
2. Set the computer for 60 WPM RTTY. Most RTTY on the Amateur HF ban s is set at 60 WPM,
170 Hz shift.
3. Select an RTTY station on the receiver. The receiver shoul be LSB. Start tuning from a low
pitche tone to a high pitche tone. When the mark frequency of 2125 Hz is receive , the
PHASE LOCK LED is on.
4. Continue tuning until you see the most pronounce ON an OFF blinking of the DATA LED.
Figure 3A

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TO CALIBRATE The MFJ-1224 Computer Interface is a juste at the factory. However,
shoul re-calibration be necessary, here is the proce ure for all frequency relate evices in the
Computer Interface.
CALIBRATION OF THE PLL FREQUENCY
1. Set the MFJ-1224 Computer Interface to receive ASCII at 300 bau , 170 Hz shift.
2. Recor from AFSK Connector of the GENERAL PURPOSE CONNECTOR, two minutes of "*" an
"U" (Capital U) repeate ly on a tape recor er. NOTE: The au io tone control shoul be set
high.
3. Play the tape back into the au io input of the MFJ-1224.
4. Observe the flashing rate of the PHASE LOCK an the DATA LEDs.
5. When the LED of the PHASE LOCK is on stea ily, an the "*" an "U" is occurring on the
screen error free, the PLL frequency is at 2210 Hz.
6. Turn the tab of the PLL trimpot until the PHASE LOCK LED is on stea ily, an the ata is run-
ning across the screen correctly. SEE Figure 4.
NOTE: The DATA LED light will emit only while ata flows. The PHASE LOCK LED will emit stea ily
when the PLL frequency is correct. In iscriminate emission of the PHASE LOCK LED means, that
either PLL is off frequency or that the au io level is too high, allowing copying of ran om noise.
CALIBRATION OF THE MARK FREQUENCY
1. Connect the computer or ra ioteletype control cable to the MFJ-1224.
2. All DIP switches in the 1224 shoul be OFF.
3. Turn the Interface On an set the front panel switches for RTTY, 170 Hz shift, an NORMAL po-
larity.
4. Enter the program into the computer. If using a ra ioteletype, go own to 9.
5. If you are using Kantronics Hamsoft™, press "K" when aske to choose "K" if using a Kan-
tronics Interface or T-User Terminal Unit.
6. Connect a frequency counter with a 1:10 probe to the AFSK output pin of the MIC jack.
7. Go to the RTTY section of the program.
8. Put the computer into RTTY TRANSMIT with no characters in the buffer. For Hamsoft™ on the
VIC-20™ this is CTRL-T. Now go to 10.
9. Put the ra ioteletype in the MARK con ition (Loop Current Flowing).
10. A just VR2 trimpot (see Fig 4.) for a frequency of 2125 Hz (±2 Hz).
NOTE:
The MARK an SPACE frequencies must be set while the Interface is connecte
to the computer or ra ioteletype.

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Calibration of 170 Hz Shift
1. Put the computer into RTTY RECEIVE. For Hamsoftt™ on the VIC™.
2. Connect a frequency counter in the same manner as setting the MARK Frequency.
3. The counter shoul rea 2295 Hz.
4. If the counter oesn't rea 2295 Hz, then a just VR3 (see Fig 4) for a rea ing of 2295 Hz (±2
Hz).
Calibration of the 850 Hz Shift
1. Set the MFJ-1224 front panel switches for 850 Hz shift.
2. Connect a frequency counter as in Calibration of the MARK Frequencies.
3. The frequency counter shoul rea 2975 Hz.
4. If the counter oesn't rea 2975 Hz, a just VR4 (see Fig. 4) for a rea ing of 2975Hz (±2 Hz).
SOFTWARE CONSIDERATIONS
DIP SWITCH There is an eight switch DIP package on the PC boar . These switches are use to
configure the inputs an outputs of the GENERAL PURPOSE CONNECTOR to work correctly with
your computer an software. The following chart illustrates functions of each switch:
SWITCH POSITION FUNCTION SIGNAL AT PIN
1 ON CW KEY LOW-KEY
1 OFF CW KEY HIGH-KEY
2 ON CW ID KEY HIGH-CW-SHIFT
2 OFF CW ID TONE LOW-CW-SHIFT
3 ON KANTRONICS PTT N/A
3 OFF GENERAL PTT N/A
4 ON RTTY INPUT LOW MARK
4 OFF RTTY INPUT HIGH MARK
5 ON GENERAL PTT N/A
5 OFF KANTRONICS PTT N/A
6 ON PTT INPUT HIGH PTT
6 OFF PTT INPUT LOW PTT
7 ON CW DEMOD OUTPUT LOW TONE
7 OFF CW DEMOD OUTPUT HIGH TONE
8 ON RTTY DEMOD OUTPUT LOW TONE
8 OFF RTTY DEMOD OUTPUT HIGH TONE
MFJ-1223 RS-232 INTERFACE

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The MFJ-1223 is use to connect the MFJ-1224 to RS-232 Ports. Since the MFJ-1224 uses
TTL voltage (+5 VDC) an RS-232 ports are ±12 VDC, a interface becomes necessary to intercon-
nect. Our MFJ-1223 allows the use of the port.
I. VIC 20™
A. Use with the MFJ-1252 or the MFJ-1264 Software.
NOTE: The connector cable supplie with the Software has the proper connections for the
GENERAL CONNECTION PORT an the VIC USERS PORT. The DIP-Switches are set at the
factory for this computer an software, an cable.
MFJ-1224 General Connector User Port MFJ-1224 DIP-Switches
RTTY DEMOD B, C, L 1 ON
CW DEMOD B, C, L 2 ON
GND N 3 ON
CW ID H 4 OFF
RTTY J, M 5 OFF
PTT (IN) NOT USED 6 OFF
CW KEY K 7 ON
B. Using Kantronics Hamsoft™ an Hamtext™ software.
NOTE: The connector cable supplie with the software will connect irectly between the K
CONNECTOR an the USERS PORT. The DIP switches will have to be set for use with this
software:
MFJ-1224 "K" Connector Control Port MFJ-1224 DIP Switches
DEMOD 6 1 OFF
GND 8 2 OFF
CW KEY 3 3 ON
RTTY 2 4 OFF
CW ID 1 5 OFF
6 OFF
7 OFF
8 OFF
C. Using RAK Electronics RTTY/CWII Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 General Connector User Port MFJ-1224 DIP Switches
RTTY DEMOD B, C 1 ON
CW DEMOD D 2 ON
GND I 3 OFF
PTT J 4 OFF
RTTY M 5 ON
PTT (IN) NOT USED 6 OFF
CW KEY K 7 ON
+5 VDC NOT USED 8 OFF

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II. C-64™
A. Using the MFJ-1265 or MFJ-1253 Software.
NOTE: The connector cable supplie with the software has the proper connections for the
GENERAL CONNECTION PORT an the C-64 USERS PORT. The DIP Switches are set at the
factory for this computer, software, an cable.
MFJ-1224 General Connector User Port MFJ-1224 DIP Switches
RTTY DEMOD B, C, L 1 ON
CW DEMOD B, C, L 2 ON
GND N 3 ON
CW ID H 4 OFF
RTTY J, M 5 OFF
PTT (IN) NOT USED 6 OFF
CW KEY K 7 ON
+5 VDC NOT USED 8 OFF
B. Using Kantronics Hamtext™ Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 "K" Connector Control Port MFJ-1224 DIP Switches
DEMOD 6 1 OFF
GND 8 2 OFF
CW KEY 3 3 ON
RTTY 2 4 OFF
CW ID 1 5 OFF
6 OFF
7 OFF
8 OFF
C. Using the AEA-SOFT an MBA-TEXT, VERSION 1.2 Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 GENERAL CONNECTOR User Port MFJ-1224 DIP Switches
RTTY DEMOD J 1 ON
CW DEMOD J 2 ON
GND 1, 12, A, N 3 OFF
CW ID NOT USED 4 ON
RTTY F 5 ON
PTT (IN) E 6 OFF
CW KEY H 7 OFF
+5 VDC NOT USED 8 OFF

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III. APPLE™
A. Using the C. H. GALFO Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 General Connector Apple Game Port MFJ-1224 DIP Switches
RTTY DEMOD 2 1 ON
CW DEMOD 4 2 ON
GND 8 3 ON
CW ID NOT USED 4 OFF
RTTY 15 5 ON
PTT (IN) 14 6 ON
CW KEY 13 7 ON
+5 VDC NOT USED 8 ON
B. Using the Kantronics Hamsoft™ Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 "K" Connector Apple Game Port MFJ-1224 DIP Switches
DEMOD 3 1 OFF
GND 8 2 OFF
CW KEY 14 3 ON
RTTY 12 4 OFF
CW ID 13 5 OFF
6 OFF
7 OFF
8 OFF
C. Using the AEA-Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 General Connector Apple Game Port MFJ-1224 DIP Switches
RTTY DEMOD 2 (PBO) 1 ON
CW DEMOD 4 (PBO) 2 ON
GND 8 GND 3 OFF
CW ID NOT USED 4 OFF
RTTY 15 (ANO) 5 ON
PTT 14 (AN1) 6 OFF
CW KEY 13 (AN2) 7 OFF
+5 VDC NOT USED 8 ON

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IV. TRS-80 COLOR COMPUTER™
A. Using the Kantronics Software.
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 "K" Connector Hamsoft Pac MFJ-1224 DIP Switches
DEMOD DEMOD 1 OFF
GND GND 2 OFF
CW KEY CW KEY 3 ON
RTTY RTTY 4 OFF
CW ID CW ID 5 OFF
6 OFF
7 OFF
8 OFF
B. Using Clay Abrams Software
NOTE: The DIP Switches must be set for this software as follows:
MFJ-1224 General Connector Seriall I/O (P2) MFJ-1224 DIP Switches
RTTY DEMOD PIN 2 1 OFF
CW DEMOD PIN 2 2 ON
GND PIN 3 3 OFF
CW ID NOT USED 4 OFF
RTTY PIN 4 5 OFF
PTT (IN) NOT USED 6 OFF
CW KEY PIN 4 7 OFF
+5 VDC NOT USED 8 ON
NOTES: 1. A TTL TO RS-232 CONVERTER MUST BE USED WITH THE CLAY ABRAMS
SOFTWARE. (We recommen the MFJ-1223).
2. PLACE A 1 µF ELECTROLYTIC CAPACITOR FROM PIN 2 (DATA IN) OF THE
SERIAL I/O TO GROUND.
Hamsoft™ an Hamtext™ are tra emarks of Kantronics, Inc.
VlC-20™ is a tra emark of Commo ore Business Machines, Inc.
TRS-80™ Color Computer is a tra emark of Tan y Corporation

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Figure 4

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