[NCARC] Addendum to the 145.115 intermod issue

[Steve Henry]

Hi folks-

KO0J reminded me of another avenue of investigation that we initially tried
that may still help.   Willis-- if you would also include this in the
newsletter that would be great.

The intermod happens most of the time in the transmitter tail.   Since there
is no 100 Hz tone coming in from a ham transmitter into the repeater during
this tail, that means that somehow 100 Hz is still coming in as part of the
intermod contamination signal. ( I've confirmed that during the transmitter
tail portion of the repeater operation, 100 Hz PL input is still required to
re-trigger the repeater input being mixed in... for a while I thought there
might be a bug in the 7K code due to changes made in the most recent
firmware ROM).

One major source of 100 Hz is the CTCSS encoder signal we have being
generated in the interface box.   I've historically turned this signal off
(prevented the 7K repeater controller from mixing it in), but unfortunately
this only shuts it off from getting mixed in with the transmit signal...
this tone is still being generated and is still a possible signal source.
With the changes we're making this weekend, it will be easy to turn this
signal off and on and have it not be a potential signal contaminant (we're
using an entirely different CTCSS encoder generation circuit that is in the
repeater itself, not in the interface box.

'73

-Steve, N7GN