Jim, This problem has bothered IC type dtmf decoders for years. One would not see it as much if controllers did not mute rx-to-tx audio for security reasons. Some controllers allow this muting to be turned on/off. Other needs for passing the dtmf, such as for echolink, can be useful.
Lowering the dtmf input level is one solution for it is easy to set the level somewhat higher than needed. To best set the level with common dtmf decoders like the 8870 and 8880 is use of a scope on pin 3, the internal op-amp output. One can see here the actual audio the decoder is decoding. Most Hams do not have access to a scope is one problem. It is rather difficult to state a proper level for there are so many variables in the dtmf audio; level, twist and level of each tone, and varying levels with the 8 tones. I usually set to about 3 V p-p from a center digit. 73, ron, n9ee/r >From: Jim Brown <[EMAIL PROTECTED]> >Date: 2008/03/27 Thu PM 11:30:46 CDT >To: Repeater-Builder@yahoogroups.com >Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller > >My experience is with the CAT-300 controllers, but I have found that if the >level to the DTMF decoder is set too high, it is a lot more prone to falsing >and covering a transmission with the cover tone. I have found that female >voices gave the most problem. Reducing the level to the DTMF decoder in the >controller cleared this up for me. > >73 - Jim W5ZIT > >"Tony L." <[EMAIL PROTECTED]> wrote: The DTMF muting >feature on one of our CAT-1000 controllers occasionally > falses and sends cover tone over a user's voice. This happens to one > user more so than anyone else. > > Is there an adjustment? Why does this happen on only one of 3 idential > controllers? > > Thanks. > > > > Never miss a thing. Make Yahoo your homepage. > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
