Vendor: AEA Bulletin: PK3848 Subject: Adjusting the PK-232 internal controls Here are tips that I hope might prove useful to others using the AEA PK-232MBX Mulitmode TNC Adjusting the AEA PK-232 TNC's internal controls There are several controls (7 in all) inside of the PK-232 multi-mode controller that may need to be checked or touched up a bit from time to time. The easiest controls to adjust are the four (4) AFSK board- mounted tone controls. They set the tone frequencies that will be transmitted during the various PK-232 operational modes. To adjust them, I use a bare-bones terminal program (like the older DOS ProComm Plus terminal program or the "Dumb Terminal" mode in PC Packratt) and use the PK-232's built-in "CALibrate" software. >From the "cmd:" prompt, type "VHF ON" and then "CAL"...you'll see a series of numbers scrolling down the screen. The first number is the VHF packet low tone, the second number is the pot designation number on the PK-232 board that should be adjusted. Nice and handy isn't it? That first number should be something very close to 1200...if not, adjust the pot R167 until it reads 1200. Now tap the space bar to shift to the VHF high tone, and adjust R165 until the first number reads 2200. These tone pots are not multi-turn, so just a slight touch will change them drastically...try to get them within a couple of cycles of the correct value...I was able to do it in mine. That takes care of the VHF tones. Type "Quit" to exit the "CALibrate" mode, the "cmd:" prompt returns...then type "VHF OFF" to enter the HF tone mode. Type "CALibrate" again and you'll see the scrolling numbers once more...but this time the first number should read 2110. R168 will adjust the 2110 tone if it's not close enough. Tapping the space bar again switches to the HF high tone, which should read 2310...if not, then R164 needs adjusting. Typing "Quit" again will exit the "CALibrate" mode. Now check the 3 remaining pots. Rig up a "loop-back" connection to the "Radio 1" input connector by shorting pins 1 and 2 on the "Radio 1 Input Connector" on the rear of the PK-232. Make sure that the front panel selector switch is on "Radio 1". Hook-up a monitor scope to the "Scope Output Connector" (on the rear of the PK-232)pins 3 and 5...using a standard cross-pattern RTTY monitor scope is the easiest and most accurate way to monitor these adjustments. You might be able to use the PK-232's tuning bargraph LED's, but the correct adjustment isn't nearly as obvious as when using a true monitor scope. You should still be in the "VHF OFF" mode, and that's fine. Don't go into the "CALibrate" mode quite yet. The scope display should show a varying "blob" of noise in the center of the display...adjust R157 (directly behind the "Threshold" control, until the "blob" is smallest in size and varying randomly. Look for a distinct "null" point. Now re-enter the "CALibrate" mode, and hold down the space bar so that the tones switch back and forth quickly...you should see something approaching two cross -loops on the the screen. Be sure that the scope's amplifiers are not being overloaded, you may need to install an attenuator pad in series with each input if the pattern looks "flattened". Now alternately adjust both R81 and R96 until the cross-pattern is most symetrical ...it should end up being two fairly equal 90 degree cross-loops. When you're satisfied, exit the "CALibrate" mode by typing "Quit", and recheck R157 for a null as described above. Even if you normally don't use a monitor scope on your PK-232, these last three adjustments are important. Here's a quick summary chart for reference when you actually perform the work: VHF ON - CAL R167 - 1200 R165 - 2200 VHF OFF - CAL R168 - 2110 R164 - 2310 R157 - adjust for a null (no tones). R81 & R96 - alternately adjust for the most symetrical cross- loops. This may not be the "only" way to perform the adjustments, but they've worked for me and I hope you'll find them useful as well.