Notes on the ICS Basic Repeater Controller from Joe at ICS 02-May-19

Too much audio is sometimes worse than not enough audio for the MT8870 decoder chip. 
What I discovered is that a resistor change on the inputs to the DTMF decoder makes 
the RX AU LEVEL pot (R29) setting much less critical. I found that often times the 
radio fed a bit more receive audio level into the controller and at that point the 
DTMF decoder was real hit and miss. If you want to make the changes to your board, 
change R20 and R26 from 10K to something in the 47K-56K range. I had a bunch of 
49.9K resistors, so that is what is in the new controllers we are shipping. I did 
send several out with 22K, but found that the higher value was even better yet. 

Here's a very helpful hint on making repeater on-off commands: disable the transmitter, 
not the receiver, or you will have to use the control receiver port to re-enable the 
receiver. I prefer to make a couple of macros, i.e. enter DTMF Command Strings into 
memory, to disable and enable the transmitter without having to put the controller 
into setup mode.

To reduce the tone audio level feeding the TONE LEVEL pot (R19), change R15 from 22K 
to something in the 47K-100K range. [Suggested by Bob WA1MIK]