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Version 1.73 Copyright © 1997 Link Communications Inc. 1/18/97
links or remotes. Sometimes you want this, so you can send tones down the links to control
other sites. Other times, you don't want tones to go down the links; in those cases you should
turn on the DTMF must for the link port transmitters just like you did for your repeater
transmitter (with command 007).
DTMF Mute Bypass:
The DTMF mute bypass can be used for sending DTMF paging codes over a repeater that
mutes DTMF digits or for passing commands out a link transmitter that normally mutes DTMF
tones. If enabled, it allows you press 'D' (or whatever your force-execution digit is - see
command 078) as the first digit after keying up to disable the muting function until you unkey.
When the 'D' is detected, the controller will ignore any digits received from that receiver until
you unkey. It will not mute those digits on any transmitter and it will not try to decode those
digits and execute any commands. The 'D' itself will be muted as soon as it is detected. If you
do not have an audio delay module, the first part of that 'D' will be heard and might mess up
whatever you are passing tones to. If the tones are going to another controller of the same kind,
turn off the DTMF bypass on the other controller so the 'D' won't cause it to ignore the digits.
If the first part of the 'D' not being muted is still a problem, you will have to get an audio delay
for that receiver, turn DTMF mute off and enter the digits without using a 'D' first, or use the
controller's command to generate DTMF digits (command 033).
Voice Falsing
As mentioned earlier, a DTMF decoder works by watching for 8 tone frequencies, 4 that
represent the row and 4 that represent the column of a 16 key DTMF keypad. If a row
frequency and a column frequency are detected at the same time, the decoder registers it as a
valid digit. Sometimes peoples' voices have those frequencies in them and cause the DTMF
decoder to think that a digit is present when it is not. If you have the DTMF mute turned on,
this will cause it to be activated and your voice will "drop out" for a couple of seconds as the
controller thinks it is muting a DTMF digit. If you have the cover tone turned on, you will hear
it as well. The voice falsing of the DTMF decoder is not the decoder's fault - it is just watching
for those tones. There are a couple of things you can do to reduce falsing. The first thing is to
check all of your audio levels. If you have the receive audio turned up too high at any point
before it gets to the decoder, it may be distorted, which adds harmonics and makes falsing more
likely. If your audio levels are OK and you still have falsing problems, you can change a
resistor that makes the decoder require that the row and column frequencies be present longer
before it considers the digit to be valid. On the RLC-Club, this resistor is R14 and on the
deluxe board it is R19. Some earlier controllers used a 300K resistor which caused the DTMF
digits to be detected in less than 40ms, but voice falsing was common. Later controllers
including all of the RLC-Club's have used a 470K resistor, which sets the decode time to about
50ms. This is still a lot faster than most people release digits, so unless you have a very fast
autodialer, it should keep up. This greatly reduces the problems with falsing. In a few cases,
persistent audio distortion problems or someone's voice will cause falsing even with a 470K
resistor. In those cases, the resistor can be replaced with a larger one to slow the decoder down
even more. Values over 700K or so should be avoided as they may keep the decoder from
working at all. You can make any remaining falsing less annoying by setting the DTMF mute
timer to be relatively short (1..2 sec, or even less if you have an audio delay module).
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