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PACKRATT PK-232 Mods - Eliminate Noise [message #3039] Sun, 01 June 2014 19:22
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Registered: December 2004
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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 results 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 possible leads 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 I would 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.
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