Ian, I suspect that the problem is "talk off" caused by overdeviation of the mike audio. When the CTCSS tone is mixed with the mike audio prior to the deviation limiter stage, an excessive voice signal will be hard limited along with the CTCSS tone, causing a distorted signal. This problem occurs quite often in Amateur-grade equipment, since the makers often have very "hot" tone deviation that is set with a fixed resistor rather than adjustable as in most commercial-grade radios. Alinco, Icom, and Yaesu handhelds seem to have this problem all the time. Every Alinco handheld I've tested has a PL deviation above 1 kHz, and a few samples were up to 1.5 kHz- about three times the necessary amount. Needless to say, a tone deviation of 1.5 kHz doesn't leave much room for voice deviation, and all it takes is a loud talker to cause the limiter to "squash" the modulating signal and distort the CTCSS tone enough for the repeater to drop. It's not easy, but I have padded the CTCSS tone circuit in several Alinco and Yaesu radios to reduce the level to less than 500 Hz deviation, and that cures the problem. Most modern repeaters can detect a tone as low as 100 Hz deviation, so setting the tone between 400 and 500 Hz should work fine.
Of course, there are "diddle-stick artists" who can't resist cranking up the mike gain pot so that they will "sound better" (they think) and make the problem worse. In order to stay within a 16K0F3E emission envelope, the total deviation should be limited to around 4.8 kHz. Most commercial-grade radios reduce the voice gain when a tone is added, but cheap radios aren't that smart. If the total deviation is limited to, say, 4.8 kHz, but a tone is not used, the voice deviation will sound softer. I suspect that the diddle-stick artist cranks up the gain to offset that low level. I suggest that you set the CTCSS deviation to 500 Hz, and ensure that the deviation limiter is set no higher than 5.0 kHz. See if that reduces or eliminates the talk-off problems. The Maxon service manual should have a procedure for mike gain and limiter setting, which should be followed. The fact that only some users have the problem strongly points to the user radios, rather than the repeater. Also, ensure that the problem radios are exactly on frequency. Please keep this list informed as to your findings and progress. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kerinvale Sent: Monday, July 06, 2009 2:33 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Ctcss dropout due to loud voice Hi guys .Can anyone suggest ways to reduce ctcss dropout when someone is talking loud on a repeater .The repeater radios are maxon pm150 (sm4450sc) and I have tuned them using 600hz of ctcss and a 1khz tone at 3kHz modulation to make sure it doesn't happen ,but I have one user that talks louder than the other users and it seems to breakup all the time for them where other users seem to have no problems.Could I make sure their ctcss from their maxon pm160 is around 600hz or 700hz or could the problem be more tied up with the receiving repeater radio Thank You, Ian Wells, Kerinvale Comaudio, 361 Camboon Road.Biloela.4715 Phone 0749922574 or 0409159932 www.kerinvalecomaudio.com.au <http://www.kerinvalecomaudio.com.au/> <http://geo.yahoo.com/serv?s=97359714/grpId=104168/grpspId=1705063108/msgId= 92448/stime=1246912865/nc1=5349274/nc2=5741391/nc3=4025338>
