TNC2.11

 Anyway, removal of the MF10 filter seems to make this phenomenon
disappear!  I suspect that this is an indirect effect, unrelated to the
filtering itself.  Removing the MF10 reduces the loading on the -5 volt
supply, which in turn may make the XR-2211 demod chip happier (the TNC2 manual
warns of degraded modem performance if any additional loading on the -5 volt
supply occurs, and there are other indications that this supply is not as
robust as it should be).

I hope these observations stimulate some interest, and I'd like to hear from
anyone who gives the modification a try.  Also, does anyone have more
information on the use of preemphasis/deemphasis in amateur FM rigs (i.e.,
which of them use it, and what the characteristics are)?  I know the modified
commercial sets will have it, as it is specified in the DOC standards, but for
amateur equipment it seems to be an unknown quantity (like turnaround time).
Sooner or later, the manufacturers of amateur equipment will get around to
giving us specifications which are useful for determining the performance of
radios for data transmission, but until that happy day arrives, I guess we'll
just have to do it ourselves.

        73...   Barry VE3KLW @ VE3PAK-1