TTL level transmit data is present on the FSKN and FSKR pins on J7 of the PK-232 regard less of the position of the RADIO 1/RADIO 2 switch. When left connected to the direct FSK keying inputs of many HF transcievers, the data on these lines will cause noise on the HF transmitted signal on other modes (SSB, FM, etc.) when the other port is being used on another radio. Further, to use direct
FSK keying, one must split the interconnect cable at the PK-232 end because the receive audio and transmit FSKN/R signals use different connectors on the PK-232.

SOLUTION:

Select either the FSKN or FSKR signal (whichever you use) and substitute it for the SQUELCH input on J4 and J6. This allows the TTL level transmit data to appear on J4 and J6 pin 3 as selected by the RADIO 1/RADIO 2 switch. This eliminates both of the above problems. This modification requires no trace cuts or drills and may be easily restored.

MODIFICATIONS:

1) Select the appropriate signal for your application.
2) Remove R150
3) Ground the base of Q6 using a jumper to the pad left by the Q6 side of R150.
4) Connect a jumper between the pad on the SW2 side of R150 and U38 pin 2 or pin 8 depending on your choice in step 1.

NOTE: The pinouts on J7 for FSKN and FSKR are reversed at U38 on some PK-232 schematics. FSKN thus appears on U38 pin 8 and FSKR appears on U38 pin 2. The labels on J7 are correct.

These modifications apply to PK-232s with serial numbers under 1000.
Four simple hardware modifications improve the PK-232's performance.

1. Change C54 from: 0.1 mfd 10% mylar (increase low-frequency rolloff) to: 0.01 mfd 10% mylar
2. Change U16 from: 74LS04 (do this only if bbRAM does NOT hold memory) to: 74HC14
3. Change R35 from: 20K 5% (improve VHF/Morse sensitivity) to: 39K 5%
4. Add: 0.047mfd mylar 10% in series with R79 (same as above)

The following might interest you (copied from K5FL MSO on RTTY):

The following information was received from Wolf, ZS6AQC, concerning new Eproms for the PK-232 PAKRATT, plus a modification to eliminate noise from the op-amps. On recommendation of OM Piet, ZS6AQC I checked the noise in the power bus to the MC34074P op-amps and found (just like he said) that there is a lot of rubbish between the pins 4 and 11 of U23, 26, 28,30,32 and 34. So, I placed some 1 microFarad caps across them and my receive noise is much less (measured on a mark=space scope cross display). In fact, I can now even copy some steady signals that don't even raise the S-meter needle. Hope you can improve yours also? This was received from OD5NG: he
made this mod and resulsts were outstanding.

Then Clark, W9CD made the modification and was pleased with the results. Consequently, I bought from Radio Shack 6 each 1 MF tantalum capacitors ("condensers" to Old Timers),and mounted them on the bottom of the board, with the shortest possibleleads in the positions described above.
The results are OUTSTANDING!!! RTTY signals I could not copy before are now perfect copy, even when you can barely see the traces on the scope. ARQ links, which could not be made before, now flow smoothly. The only thing I don't know if the mod will work if the latest version of the PK232 firmware upgrade is not installed, but Iwould think that it will. Give it a try and you
will be pleasantly surprised.
P.S.: The part number for the referenced capacitors is:
Radio Shack # 272-1434, 1 MFD 35 Volts (Tantalum). Cost $ .59 each.

1. The PK-232 will cause ssb and fm distortion when plugged in to a TS-680 (aux port). My fix has been to add a 470 pF. Hi-Q disk cap. in series with the TX-audio line, and leave the mic gain at maximum. I also have the 600 ohm divider resistor (R 151 radio 1) lifted but don't know if it still helps after the cap mod.
2. When switching from Com-Fax to ComPakratt cartridges the RTTY Rx-after-Tx key F7 is disabled. The fix is to enter Terminal mode on ComPakratt (<C=> t) and then enter conmode converse.

3. I have received mods to convert the PK-232 into a dual-port tnc for gateway dual-rig use from VE7DIE. Drop him a note if interested.

Through personal experiences with the PK-232, I have found that a somewhat strange problem seems to have been isolated. I had recently had some difficulty with the PTT not holding solidly on transmit. It seemed almost attributable to the buffer/data flow into the unit, as the problem seemed to lessen in severity when the threshold adjustment was increased so the unit could not transmit;
then by backing it off, it would send a packet stream without incident.

By accident almost, I finally decided to drop the input voltage to the tnc (which had been fed by 14.5 volts -- sharing a common power supply as the transceiver). This immediately cleared the "chatter" problem. Apparently, the 232 uses the input voltage in a number of places, one of which is in the PTT
control circuit. Unlike the 5 volt stages, the 13 volt supply is NOT regulated and thus whatever the input voltage is, that's what the "13+ volt" bus would be.

If anyone has similar problems with the PK232, it would seem that you have 3 choices:
1. Buy an AEA or similar transformer to supply fixed 12.6 volts to the unit.
2. Drop your power supply voltage to this point and sacrifice a little bit of power/performance from your transceiver
3. Put in a separate 12 volt regulator circuit for the 232 separately.

I hope this has been of help for anyone who may have incurred similar difficulties.

IN ADTION TO WB2ZTK'S NOTE ON MSG. #329 ABT THE INTERALLY UNREGULATED SUPPLY, THIS CAUSES ADDITIONAL PROBLEMS. IF OTHER RELETIVELY HIGH POWER EQUIPMENT IS TURNED ON OR OFF, THE RESULTANT "GLITCH" ON THE AC LINE COULD AND HAS CAUSED THE PK-232 TO "LOSE ITS MIND" REQUIRING THAT IT BE TURNED OFF FOR A SHORT WHILE (NO INTERNAL BATTS), TURN IT ON AND HV PC-PACKRATT RE-INITIALIZE EVERYTHING. (A PAIN) THIS HAPPENS WHEN I INADVERTENTLY OPEN OR SHUT-OFF MY IC-735 PLUGGED INTO THE SAME LINE
(117VAC) AS THE PWR FOR THE PK-232. IT DOESNT ALWAYS HV THIS EFFECT, LEADING ME TO BELIEVE THAT IT DEPENDS WHERE THE AC LINE WAVEFORM HAPPENS TO BE ALONE IN ITS CYCLE WHEN THE PWR SWITCH IS USED. IF THE WAVEFORM IS NEAR ITS ZERO CROSSING OR AT A LEVEL THAT IS LIKELY TO CAUSE THE LEAST AMOUNT OF INDUCTIVE KICKBACK FROM THE PWR. TRANSFORMER TO PROPAGATE.

TO CAUSE PROBLEMS THE 12V REG. THAT DAN SUGGESTS WITH A 13V INPUT OR EVEN TWO 15V ZENER DIODES BACK TO BACK WITH A 100uf ELECTOLYTIC CAP IS WHAT I USE IN PARALLEL WITH MY SUPPLY NOW WITH GOOD RESULTS. THE BEST PLACE TO PUT IT IS IN THE TNC'S CABINET OR AT LEAST AS NEAR AS POSSIBLE TO IT EXTERNALLY.

All users with PK-232's and PK-87's can use the MBX command in the following manner with the NET/ROM nodes. Normally, MBX call1 monitors packets being sent by "call1", such as from a BBS, etc. MBX call1,call2 monitors just text being exchanged between those two stations. (Presumably it should also prevent other packets from being included which were being sent to other stations, but for some reason other packets find their way to the display with W6IXU multibox.) With the NET/ROM nodes going up, here's some info for using MBX for proper monitoring:
If the user is local and going to another user with just the one local node, use local-15,remote. For instance, WB6WKB is using the node W6AMT-3 to get to WB6SAN, the node will be using WB6WKB-15 to talk to WB6SAN. The MBX should be set to WB6WKB-15,WB6SAN. If WB6WKB is talking up the network to someone else, use the node's callsign instead, since it's whom WB6WKB is actually talking to. In this case, set MBX WB6WKB,W6AMT-3 (assuming W6AMT-3 is the node involved and WB6WKB is visible to you). Internode exchanges and transmissions from the node to other stations are not shown. It's the next best thing to being the connectee! MBX does not work on two callsigns which are not connected to each other, so you can't follow two BBS's simultaneously.
Otherwise, I've found it very useful, many times saving me the hassle of having to connect to read the newest messages or to download the latest Pathefinder or Gateway.

THERE IS A BUG IN THE LATEST VERSION (1.06) OF THE AEA PC PAKRATT PROGRAM FOR USE WITH IBM PC OR COMPATIBLE COMPUTERS. IF YOU ATTEMPT TO CHANGE THE PACKET PARAMETER SQUELCH AT THE PARAMETER WINDOW FROM THE DEFAULT VALUE OF NEG TO POS, THE PROGRAM WILL ABORT AND GIVE YOU THE ERROR MESSAGE:
.
RS-232 LINK ERROR - WILL REINITIALIZE - PRESS ESC
.
AND AFTER PRESSING ESCAPE, THE PROGRAM WILL TRY TO RE-ESTABLISH A LINK WITH THE PK-232 AND PRESENT THE MESSAGE:
.
PARAMETER DOWNLOAD ERROR
PLEASE REFER TO YOUR PC-PAKRATT MANUAL.
PROGRAM TERMINATING.
.
UNFORTUNATELY, THE PARAMETER DOWNLOAD ERROR MESSAGE ISNT MENTIONED ANYWHERE IN THE MANUAL.

THIS BUG APPARENTLY DOES NOT PRESENT A PROBLEM TO THE VAST MAJORITY OF PK-232 USERS. IT NEED NOT CONCERN YOU IF:
.
YOU HAVE NOT CONNECTED THE SQUELCH SIGNAL LINE BETWEEN YOUR TRANSCEIVER AND THE PK-232 (PIN 3 OF THE RADIO 1 AND RADIO 2 INTERFACE CONNECTORS), OR
IF YOU HAVE MADE THE CONNECTION, LUCKY ENOUGH TO OWN A TRANSCEIVER THAT PROVIDES THE CORRECT SIGNAL SENSE TO THE PK-232 FOR THE PROPER OPERATION OF RF-CARRIER CSMA WITH THE PROGRAM DEFAULT VALUE OF NEG FOR THE SQUELCH
PARAMETER.
.
THE BUG IS EXHIBITED WHEN THE PROGRAM INCORRECTLY ATTEMPTS TO SEND THE COMMAND SQUELCH POS TO THE PK-232. WITH RELEASE 25 JUNE 1987 FIRMWARE, ALLOWED VALUES FOR THE SQUELCH PARAMETER ARE ON, OFF, OR NEG. THE VALUE POS CAUSES THE PK-232 TO RETURN AN ERROR CODE TO THE PROGRAM, WHICH THEN ABRUPTLY CRASHES.
.
FORTUNATELY, THE FIX FOR THIS BUG IS SIMPLE. IT IS ONLY NECESSARY TO CHANGE THE PROGRAM TO SEND THE ALLOWABLE VALUES FOR THE SQUELCH PARAMETER TO THE PK-232. THE PATCH BELOW WILL REPLACE THE PROGRAM VALUES OF NEG AND POS WITH OFF AND ON RESPECTIVELY.

.
USING THE DOS DEBUG UTILITY, ENTER THE FOLLOWING:
.
DEBUG UTILMOD.CHN
-E 614C 20 4F 4E
-E 6160 4F 46 46
-E 6174 20 4F 4E
-W
-Q

AFTER SPENDING A NUMBER OF HOURS BUILDING SOME VERY NICE INTERFACE CABLES, I WAS FRUSTRATED TO THINK THAT I MAY OF HAD TO MODIFY THEM TO COPE WITH A PROGRAM BUG. AEA IS AWARE OF THE PROBLEM, BUT THEY HAVE NOT YET CORRECTED IT. I'M GLAD THAT I WAS ABLE TO COME UP WITH A REASONABLE FIX, AND HOPE THAT THIS INFORMATION PROVES USEFUL TO SOMEONE ELSE.
.
SEE YOU ON THE DIGITAL MODES?

PK232 Mods for AMTOR ARQ

Have you ever attempted to work AMTOR 'ARQ' with software that does not give you split screen?. Well for example when using the TRS-100, or 200 or the APPLE 2E, and compatibles that have no software which allows you to split the screen.

There is a modification in the april issue of QST, page 28 regarding the - ECHO AS SENT- (EAS) command, which is udes in the AMTOR mode to allow you to see on the screen the buffer that is being transmited, as well as echoing back what the other station has acknowledged.

This can be done with the (EAS) CMD, but once the command is turned on there is no way to turned it off in the middle of the QSO. If the (EAS) is left on during the QSO, there is a tremendous amount of confusion on the screen, which can drive you crazy.

Therefore the only way to turn off the command is with a switch installed on the PK-232.

If you read the article by AD7I which attempts to explain his modification, it can also drive you crazy. The schematic shown in the article is fine, but he fails to explain that the whole thing is as simple as installing a switch, one lug of the switch connected to R-179 (THE END CLOSEST TO U-7, PIN 7) not closest to U1, PIN 7 as indicated in the article. There is a typographical error on the top line of paragraph 3 on PAGE 29. So be careful because you're not going to find R-179 near U1 on the PK-232 board.

The use of the comparator circuit shown in the article was used in order to avoid drilling a hole in the front panel of the 232, but in fact you don't have to drillI a hole to install the switch. The switch can be
installed in a very small plastic box, and simply attached to the 232 cabinet by tape or VELCRO.

I read the article 10 TIMES, and started to build the comparator circuit, when I decided to read it again, because there was some confusion. Then buried in the text, there is one small paragraph that clarifies it all.

this should read...

If you want to install a switch instead of building the comparator circuit, just simply wire a SPST toggle switch to R-179 (THE END CLOSEST TO U7, PIN 7) and connect the other lug of the switch to R-135 (THE END CLOSEST TO U5) and that's all there is to it.

So if you are using AMTOR with a terminal program that has no split screen this MOD is excellent. My thanks to AD7I who wrote the article, but perhaps QST did some editing and the whole thing became very CONFUSING.
at least it appeared to me that way.

1.) Kill power, remove all cables label them if necessary electrostatic handling precautions must be utilized.
2.) Remove the top cover by removing all six cover screws, side and rear.
3.) Remove the knob on the threshold control along with the nut which fastens the threshold pot to the front cover.
4.) Remove the entire PC Board by removing all 6 fastening screws.
5.) With the front of the board facing you, locate U-23, an MC34074-P, on my unit (S/N 21186) all of these type chips are colored shiny black and marked "JRC" as opposed to a flat black type packaging on all other IC's. In addition, all of the chips addressed by this mod are on the right hand half of the board. Flip the board over and mark the socket with a felt tip type pen. Also mark pins 11 and 4 which are adjacent to each other. Continue this same procedure with U-26, 28,30, 32 and 34.
6.) With the P.C. board positioned foil side up very carefully install a bypass capacitor across pins 11 and 4. In all cases pin 11, toward the rear of the board, is the minus side. Pin 4, toward the front of the board, is the plus side.
Ideally a ceramic .1 UF @ 25 V or higher, and an electrolytic 1.0 UF @ 25 V or higher should be paralleled across the pins. The two different types of capacitors tend to provide alternate paths and avoid strange resonances that can occur when only one unit is used, providing more effective
bypassing action. A fair amount of dexterity and attention to detail must be utilized by the technician.
If you aren't fully confident of your abilities in this area, it is suggested that just one capacitor in the .1 UF to 1.0 UF range be installed.
Also ceramic types are the most effective types, tantalums are not so effective.
7.) After carefully inspecting your work especially for shorts to neighboring pins, re-assemble the unit and properly re-connect all cables. I think, that like all others that have implemented this
modification, you will be amazed at the enhanced weak signal receive capabilities.

I've just completed my work on the PK 232. I mention earlier in the week of a problem with the PK 232 regarding RFI and how the 13 volt supply line is unprotected from accidentally placing voltages above 13.6 into that box.
This 13.6 v line is connected to a couple of IC and branch to many transistors
and is use as a pull up voltage for many circuits within the box.

Well now that the highly stable voltage regulator in in place along with a RF choke of 20 uH. I can easly hear some of our checkins during the my Faxnet on 28.450. The RFI from that box was of the low level type and was knocking out the weak station when the unit was on.

I am very happy with the addition for two reasons.

1. It protect the PK 232 from Murphy and I.
2. It gives my rig isolation from the RF that was leaking down the power supply leads to a common power supply shared with the rigs and other devices.

For those that plan to add this protection, you'll find plenty of room inside the PK 232 to place this additonal Voltage reg. You might want to consider adding a bridge rectifier and 120 to 18 v @ 1 amp transformer, and connect the voltage regulator to that. I feel that the voltage regulator should be internally placed in the PK 232 along with the choke because of the leakage that was coming from the leads to a external supply. Some will find that placing ferride beads to help from this leakage, and keeping their external supply as is. Well some of us use power supplies that are ajustable and might apply voltages above 18v to the PK 232. The internal voltage regulator protects against this over voltage and choke blocks the RFI, this placement makes the best sense to me and thats how I went.

Are you having trouble with your PK-232 Locking up (not returning to receive mode) when a high RF signal is present? If so AEA says to add a .01 MFD Capacitor across D30.

D30 is located in lower right hand corner of Main Board, parts pictorial page I-1 of operating manual, just to the left of JP2 and JP3 beside SW-2.

AS A RESULT OF THE BULLETIN I SENT ON USING 2 TNC'S ON ONE RTU, SEVERAL HAVE REQUESTED THE SPECIFIC DATA ON THE PK-232 TNC.
THERE ARE SEVERAL WAYS TO MODIFY THE PK-232 TO ACCOMPLISH THE DATA INVERSION ON THE SQUELCH OR REC. DATA LINE (RF-DCD). I HAVE A HEATHKIT HK-232 SO I'LL USE THAT FOR EXPLANATION...HOPEFULLY THE CKT DESIGNATIONS ARE THE SAME AS THE AEA PK-232. THE FOLLOWING IS A CROSS REF TO PIN #'S:

DATA MFJ-1270 RTU PK-232

---- ------ ------ ------
GND PIN 2 ------------- PIN 2 ------------ PIN 4
TX AUDIO PIN 1 ------------- PIN 1 ------------ PIN 2
RX AUDIO PIN 4 ------------- PIN 4 ------------ PIN 1
PTT PIN 3 ------------- PIN 3 ------------ PIN 5
RF-DCD (SQU) PIN 5 ---->------- PIN 3 ------- 1N914 1N914

* THE SQUELCH LINE MUST HAVE THE LOGIC SIGNAL INVERTED TO WORK . THIS CAN BE DONE INTERNALLY BY CHANGING Q6 FROM A NPN TO A PNP TRANSISTOR. GARDEN VARIETY WORKED OK (2N3906 OR 2N2905 OR EQ.)
THIS APPROACH REQUIRES REMOVAL OF Q6 AND REPLACING IT WITH THE PNP AND ADDING A "PULLUP" RESISTOR 47K FROM +5V TO THE INPUT SIDE OF R150 THIS CAN BE DONE ON THE CKT BOARD SINCE R149 HAS 5V ON THE END NEAREST THE FRONT PANEL AND THE PULLUP
SHOULD BE ATTACHED THERE AND TO THE END OPPOSITE THE FRONT PANEL ON R150.

IF YOUR PK-232 IS SOU PREFER NOT TO MODIFY IT YOU CAN INSTALL A CKT EXTERNAL BY ADDING A 2N2222 TRANSISTOR AND 3 RESISTORS HERE IS THE CKT :

PK232 PIN 3 <--- -----------------------------> +5V

# 5K RES. # 47K RES

-----\ |
C \ 47K |

2N2222 -----#------------------->----> TO KEY LINE
E / B IN 914

/

---------- GROUND

THE ABOVE CKT CAN ALSO BE ADDED INSIDE THE PK-232 AND USE THE AVAIL +5V SUPPLY . THE ABOVE CKT IS THE ONE I'M PRESENTLY USING AS IT PROVIDES EXCELLENT ISOLATION FROM THE RTU'S TO THE PK232. I INSTALLED THE CKT INSIDE THE 232 ON TOP OF TAddress any queries to JIM/W5IFP @ W5IFP

TTLevel transmit data is present on the FSKN and FSKR pins on J7 of the PK-232 regardless of the position of the RADIO 1/RADIO 2 switch. When left connected to the direct FSK keying inputs of many HF transcievers, the data on these lines will cause noise on the HF transmitted signal on other modes (SSB, FM, etc.) when the other port is being used on another radio. Further, to use direct
FSK keying, one must split the interconnect cable at the PK-232 end because the receive audio and transmit FSKN/R signals use different connectors on the PK-232.

SOLUTION:

Select either the FSKN or FSKR signal (whichever you use) and substitute it for the SQUELCH input on J4 and J6. This allows the TTL level transmit data to appear on J4 and J6 pin 3 as selected by the RADIO 1/RADIO 2 switch. This eliminates both of the above problems. This modification requires no trace cuts or drills and may be easily restored.

MODIFICATIONS:

1) Select the appropriate signal for your application.
2) Remove R150
3) Ground the base of Q6 using a jumper to the pad left by the Q6 side of R150.
4) Connect a jumper between the pad on the SW2 side of R150 d U38 pin 2 or pin 8 depending on your choice in step 1.

NOTE: The pinouts on J7 for FSKN and FSKR are reversed at U38 on some PK-232 schematics. FSKN thus appears on U38 pin 8 and FSKR appears on U38 pin 2. The labels on J7 are correct.

This little piece of software could be of some help to those PK-232 users who feel tired by lack of hardware clock on their otherwise fine units.

This program is VERY SIMPLE and does just plain transfer of the time and date (not necessarily UTC though) from your computer to your PK. It is meant to be called from your AUTOEXEC.BAT file before you call the communications program you use, i.e. PROCOMM.

I wrote it in BASIC, but you may compile it to get a "pure EXEcutable" file.
Here it is:

10 OPEN "COM1: 9600,N,8,1,CS,DS,CD" AS #1
15 T$=TIME$:D$=DATE$
20 HOUR$=LEFT$(T$,2)
25 MINUTE$=MID$(T$,4,2)
30 SECOND$=RIGHT$(T$,2)
35 MONTH$=LEFT$(D$,2)
40 DAY$=MID$(D$,4,2)
45 YEAR$=RIGHT$(D$,2)
50 PRINT #1, "DA ";YEAR$;MONTH$;DAY$;HOUR$;MINUTE$;SECOND$
55 CLOSE #1
60 SYSTEM

Before you type this in, modify line 10 to match settings of your PK-232 (i.e. look up Line Settings if you use PROCOMM). Also mind COM1 used. Save it as PK_CLOCK.BAS, for example. Then add somewhere to your AUTOEXEC.BAT
the following:
.
.
.
BASICA PK_CLOCK (or just PK_CLOCK if you compiled it to PK_CLOCK.EXE)
.
.
.

You will have to specify the path to BASICA.COM and PK_CLOCK.BAS, of course.

Now, each time you turn your HI-TECH stuff on you will enjoy this little comfort of allowing the computer to tell the PK-232 what time it is, hi.

PK232SAT

The PK-232 can copy satellite telemetry from AO-13 and Uosat 9 and 11. A minor hardware modification is needed to copy Uo-11. Satellite related bulletins as well as satellite status reports are sent in plain text for part of each telemetry frame daily on AO-13 and most days on Uo-9 and 11.

The following settings will copy AO-13 SSB Baudot RTTY telemetry which is sent on 145.812 Mhz on the hour +15 and +45 minutes when operating mode B and on 435.651 Mhz on the hour +00, +15, +30 and +45 minutes when in mode JL:
BA, RXR = OFF (mode B), RXR = ON (mode JL), WI = OFF, RB 50

The following settings will copy Uo-9 and Uo-11* FM AFSK ASCII telemetry on 145.825 Mhz (if not heard try 435.025 MHZ):
AS, WI = ON, AB = 1200, (RXR is inoperative at this speed)
* The hardware modification discussed below is needed to copy Uo-11.
Frequencies are plus or minus doppler shift. An oscilloscope connected to the PK-232 will simplify keeping up with the doppler shifted tones on AO-13 as a shift in the cross pattern is seen easier than a shift of the PK-232's leds. Tones do not change with doppler on the Uosat birds as they are FM AFSK.

RXR does not operate above 300 baud because of hardware limitations. As Uo-9 sends normal shift this is no problem. But to copy Uo-11's inverted shift an unused inverter in the PK-232 (U15 pins 1 and 2) must be wired to a switch in series with the output to JP4 as follows:
1. Solder a jumper wire between U15's pins 1 and 6.
2. Cut the circuit board trace connecting U15's pin 6 to the inside pin of JP4. This trace is easiest to cut where it comes out from under R20 on the top (component side) of the PC board. Be sure to double check that this is the correct trace with an ohm meter. Cut with care (with a sharp X-acto
knife) so adjacent traces are not touched.
3. Mount a SPDT switch on the front panel where it will not interfere with other components (like near the upper left corner by the AEA logo).
4. Connect the center of this switch to the inner pin of JP4 or the trace that goes to it (which was cut to disconnect it from U15 pin 6).
5. Connect the switch contact which will be "RXR OFF" to U15 pin 6.
6. Connect the switch contact which will be "RXR ON" to U15 pin 2.

As you have the PK-232 apart, this is a good time to sand off all the paint where the two cabinet shells mate and screws fasten to improve RFI shielding. Star washers under the cabinet screws will also improve grounding. This reduced PK-232 RFI into my receiver. Toroids on all cables connected to your receiver may also help reduce RFI.

Now you can copy Uo-11 with the same settings as for Uo-9, but with your new hardware RXR switch "ON". Be sure to return it to "OFF" when you want to return to normal operation, as this switch is on line for all modes when the PK-232's internal modem is used.
If you have an HF RTTY modem you can use this with the PK-232 to improve copy of AO-13, (as well as greatly improve terrestrial HF operation of the PK-232) as the lack of individual tone filters and 200 Hz shift of the PK-232 results in less than optimum decoding. I found that with my HF modem's 170 Hz shift (which is AO-13's RTTY tone shift) and separate tone filters I can copy AO-13 RTTY telemetry from horizon to horizon error free, while the PK-232's internal modem will return occasional errors until the signal reaches a high enough strength to overcome the PK-232's modem's bandpass (not separate tone) filtering and 200 Hz shift limitations.
Also on HF RTTY I can copy weak signals with a greatly reduced error rate.
All you need do is wire in 3 double throw switches with the center pins of JP4, JP5 and JP6 connected to the center lugs of your double throw switches.
Then wire the inside and outside pins of JP4, JP5 and JP6 to these switches so that the JP center pins are switched to the inside pins for the internal PK-232 modem or to the outside pins for your external modem. These switches can be mounted on the front panel where space permits (like the
upper right corner under "model PK-232"). To ease future servicing I recommend not soldering directly to the pins on JP4, JP5 and JP6. Check your catalogs (or local electronic supply store) for DIP connectors that are .100 center/.040 square hole size and wire your switches to them. Be sure to mark each connector so you'll always reconnect them to the correct pins in the future. A look at the PK-232 schematic will clearly show you what you are doing. A triple pole double throw switch would be nice if you can find one. I made do by ganging a SPDT and DPDT together.
Earlier PK-232's connected the middle pins of JP4,5,6 to the inner pins with a circuit trace on the bottom of the PC board. These three traces must be cut.
Check beneath the JP pins to see if your model has these traces. Current models use three removable jumpers that will not be needed with the switches.

The above information is based on my own experimentation and several conversations with the helpful technical staff at Advanced Electronics Applications (AEA). The Uosat 11 hardware mod was published by AMSAT-UK in their monthly OSCAR NEWS #73, October 1988.

A list of programs for determining satellite passes can be obtained from PROJECT OSCAR, P.O. Box 1136, Los Altos, Ca. 94023-1136 and from AMSAT, P.O. Box 27, Washington D.C. 20044. Everyone interested in satellite activities is invited to check into the Tuesday night East Coast, Central and Pacific Coast AMSAT nets on 3840 Khz (+/- QRM) at 8 PM local time. Two meter AMSAT nets also are active in some areas. Contact AMSAT or Project Oscar for more information on these nets and for other satellite related information. Join the space age today.