At 2/23/2007 07:05, you wrote: >Ok, I know all the usual reasons for using input tones on a repeater, >but I have more of a theoretical performance question. Again, I'm >putting together a portable VHF repeater out of a pair of Icom mobiles >(IC-F121) for search-and-rescue use. Since it's for temporary, >emergency use, my primary concern is weak-signal performance, >particularly being able to hear someone out in the field with a 5W >handheld and a rubber duck. Here's my question: For the best chance >of allowing my repeater to hear that weak signal, am I better off >using an input tone and turning the receiver squelch way down (perhaps >even all the way), or using no input tone and plain old carrier >squelch (at a higher level)? I'll almost certainly end up using a >receive tone on this thing anyway just to minimize interference >potential, but it seems to me that doing so might help improve my >"ears" as well. Comments? > >Brian >K9JVA
Generally speaking, CTCSS squelch is slightly more sensitive than noise-activated carrier squelch. However, either one, when properly adjusted, should afford sufficient sensitivity so as to not reject intelligible signals. A very common practice is to logically "AND" the CTCSS & carrier squelch outputs to provide squelch tail reduction (or in the case of Micor squelch, squelch tail elimination on strong signals) while only allowing signals intended for repeating to activate the system. That way you get the best of both squelches. Alternatively, you can use only CTCSS squelch with an audio delay module (ADM) to eliminate the squelch tail, but the CTCSS board will need to have a rather fast decay & the ADM has to be set to a long delay value. Bob NO6B
