TAPR

From: K4DMU@WA4UMR
TAPR DCD mods - a review.


                       The TAPR DCD modifications.

                     A review by Joe Leitsch , K4DMU

        During the latter part of May and early June, 1989, I purchased

  constructed and installed four TAPR DCD modification kits- two of the

  XR 2211 Upgrades for an MFJ 1274 and Heath HD4040 (TNC 1 clone) and

  two of the State Machine Upgrades for a Kantronics KPC2 (which wound

  up in a Kantronics KAM) and an AEA PK-232. The following paragraphs are

  my personal experiences and thoughts on the project.

        I tackled the XR 2211 kits first. The only difficulty I encountered

  was an undocumented change in the pc board. There is an area on the

  upgrade board marked "J" that consists of two holes that are strapped

  with a piece of wire for VHF operation and which are wired to a 100K

  pot which adjusts the noise threshold when used on HF. Apparently there

  was a change in the board artwork after the assembly instructions were

  printed, because the "J" holes are CONNECTED by a printed trace on the

  solder side of the board. Therefore, for VHF operation, no jumper is

  needed, but if the threshold adjust pot is to be installed, the builder

  must cut the trace between the "J" holes for the pot to work. 

        Otherwise, the 2211 mod seems to work as advertized. I am able

  to run both TNCs on an unsquelched FM radio with no DCD action until

  a valid Packet transmission is recieved. This results in a quicker

  decode time for the transmission, and if the mod were made at both

  stations, a reduction in TXD time would certainly be possible.

CONTINUED IN FILE TAPR.1