MFJ-1270 Modifications



Improved DCD Performance Modification

The MF-10 filter circuit severely limit’s the decoding capability of the MFJ-1270 TNC. Once you perform the this modification you will experience very noticeable improvement in the ability of the TNC to decode more packets than ever before.

1. Remove U18 (MF-10).

2. Remove U17 DIP Header.

3. Connect a 1000pf capacitor from U17.8 to U18.1. You can remove the sockets for U17 and U18 completely if you desire or plug the 1000pf capacitor into socket pins U18.1 and U17.8. I prefer to remove the sockets and insert the capacitor on top of the board where the sockets use to reside.

4. Remove C36.

5. Replace C35 and C42 with a 0.01uF capacitor.



DCD modification for open squelch operation

This modification will allow your MFJ-1270 to operate with the radio's squelch completely open.

1. Replace R73 with 180K ohm resistor.

2. Place a 0.01uF capacitor in parallel with 180K ohm resistor and connect it between U20.3 and U20.6.. I chose to put it on top the board between R73.2 (pin connected to U20.3) and CR15.A (pin connected to U20.6). (see pictures below)




This page was last updated on 21-Aug-2013