TNC2.3
Apart from improving the copy of some signals, the removal of the MF10 had an
unexpected beneficial side-effect.  I immediately noticed a dramatic decrease
in the rate of DCD falsing on noise (I run the receiver unsquelched, which is
essential for weak signal reception and fast receiver risetime).  Apparently
much of the false DCD activity is caused by noise at the high end of the audio
passband which was being unduly emphasized by the MF10 filter.  One further
side-effect: I have often noticed that my TNC2 would give a continuous DCD
indication when there was NO input signal applied (i.e., with the receiver
turned off or squelched).  I have no idea how common this phenomenon is, but
at least one other amateur has mentioned having this occur (I believe his was
one of the MFJ TNC2 clones).  It may not represent a serious problem, but it
is a bit disturbing, and it indicates to me that all is not well in the
demodulator. 
CONTINUED IN FILE TNC2.11