"How to Use the ST-8000 in Front of Your PK-232 By Bob Boyd - W1VXV ".
Many of us have used AEA PK-232's since they first came out, have gone on to other boxes, but have kept the 232's for various reasons. I've kept mine because my laptop doesn't have a sound-card, and I can fit the PK-232, TS-440S, a power-supply, and other stuff into a pilot's map-case. Thus the physically smallest RTTY solution until recently has been the PK-232; the DXP38 changes that. I've used the PK-232 from zone 2 and from HB0, and I hope to go digital again from those and other even rarer locations in the future. I recently responded to someone that I had installed Timewave's new DSP kit into my PK-232, and that it worked OK but that I wished that the user could vary the bandwidth because I did not feel it was narrow enough for contesting. Jay, WS7I, gave me a nudge in the ribs by saying "use your ST-8000 as an external modem to the PK-232". I'm not sure why I had not done so, as I had installed a toggle switch into the 232 several years ago so that I could play with an external modem ahead of my PK-232. Anyway, Jay gave me the kick I needed. If you'd like to try an external modem with your PK-232, or you want to try multi-mode software with your ST-8000, here's how to do it.
PLEASE make sure that your PK-232 operates properly BEFORE making any of the following changes. I'm assuming in this discussion that the external modem is an ST-8000 but it could be something else! Users of the PK-232 know that there is "another one of those damnable 5-pin molex connectors" on the back of the 232 labeled 'EXT MODEM'. Timewave sells a cable with the connector affixed; ask for the PK-232RCA radio cable assembly which sells for $7.50 plus shipping. This will provide connection to the ST-8000 or other modem which you plan to use in front of the 232. (I've found it is best to clamp those 5-pin cables to the cabinet of the 232 to reduce flexing on the molex connectors.) Most of you will not already have installed a mini-toggle switch on the front panel of the PK-232, as AL7BB (I hope I have the call correct) described years ago in RTTY JOURNAL. The best place for the switch is in the upper-right hand corner of the front panel. I used a SPDT with a center off position. (When I want to stop all print on the screen I put the switch in the center-off position; this is simpler for me than turning a squelch or other control.) Label the switch positions INT and EXT, or something similar.
Inside the 232 near that EXT MODEM connector, on the motherboard you should find 3 three-pin jumper-blocks labeled JP4, JP5, and JP6. One pin of each jumper block goes to that EXT MODEM connector to provide the RX DATA, TX DATA, and DCD signals. Remove the jumper on the JP4 block and wire the switch so that you can switch the PK-232 (center of the block) to either the internal modem (inside pin) or external modem (pin nearest EXT MODEM). Don't do anything with the other two blocks. (Instead of soldering, I used a wire-wrap gun.) Only two of the wires in the five-pin EXT MODEM cable need to be used. Pin 1 is RX DATA (receive data from the external modem) and pin 4 is ground. Those two wires need to go to the DB-25 connector called Terminal Data on the ST-8000 (pin 3 is RXD and pin 7 is signal ground)**. After double-checking everything, it is time to apply power, place the newly installed modem switch in INTERNAL position and make sure that the 232 works just as it did prior to any modifications. If not, go back and correct the problem now. If OK, switch to EXTERNAL, power-up the external modem (ST-8000 or other) and try receiving a signal.
If not OK, you either have a problem in the switch or cable. If OK, congratulations.
(If you're using a ST-8000 and PK-232, you have now put $4000 of variable filters in front
of a $250 box!) Seriously, there's quite a difference; go back to the ST-8000 manual and
learn exactly how to use the ST-8000 tuning control to vary filter bandwidth! WF1B
software, which works great with either PK-232 or a 'baudot box', serves well in these
tests. Other multi-mode s/w can follow. Questions will be gladly answered to the best of
my ability
Best regards, Bob Boyd - W1VXV ([email protected])
** There is a slight error in the old write-up on how to hook the
ST8000 to the PK232...
The article says to use RXD (pin 3) on the ST8000 Terminal connector....this forces the
operator to run the ST8000 in the reverse mode...and effectively makes the Regen feature
inoperative.
Pin 10 of the same connector is also a RXD...but of a different polarity than pin 3...and
allows the ST8000 to run in the normal mode and allows the Regen feature to be used...
Again, not a big deal but if anyone refers to this information, they will encounter the
same problem as I did...
All the best...
73/ Regards...Lou N2TU