Ron Wright wrote: > 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.
Or just because muting DTMF gives a FALSE sense of security... turn muting off and let the users use all those fancy features in their modern rigs for DTMF paging, etc... is what we decided to do. It also makes it a lot easier for us to hear when someone's "frustrated" that the "darn thing" won't respond (IRLP, the controller, whatever feature they're trying to use) and we can hear that their DTMF is ultra-hot, distorted, and generally crappy. We have one user who's using some very old odd-ball Icom rig that has a pre-amplifier adjustment on the mic, and Icom kindly stuffed the DTMF through it... so the DTMF from his rig goes up and down with his mic gain settings. It took three on-air rounds of me explaining what I could hear was happening to him -- and now instead of fixing it, he just turns the gain down for DTMF and back up to talk... and often forgets to turn it back up... "X1XXX for the IRLP... [fiddling noises with the pre-amp then digits that still sound horrible but the IRLP can barely decode them]... [IRLP announces it's connected]... This is X1XXX calling CQ via IRLP. [So low deviation you can only tell it's him if you turn your rig all the way up.]" If we were muting DTMF, we'd have had no idea why he was complaining. And he STILL complains that it must be "something wrong" with IRLP. > 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. This voltage is controller design dependent... stating a "general" rule for any particular design is probably not as good as asking the manufacturer what they design to for their op-amps, etc. S-Com specifically calls out 2V P-t-P at various stages in their designs, for example. We almost never see DTMF falsing on our 5K and 7K controllers. Nate WY0X
