Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Ron Wright wrote: Nate, I've been designing 8870s and 8880s in things for over 15 years. Good chip and it has lasted. Pin 3 is simply the output of the internal op-amp and using a feed back resistor to 2 and driving with another one can set the AC gain over a wide range. The gain is feedback/driving resistor unless you wish to drive the non-inv input. The 1/2 Vcc source, pin 4, was cleaver by Mitel to simply use with a single 5 V supply. As to the other gain pins it is best not to use these for some other manufactures of the chip do not provide them. California Micro Devices, probably one of the biggest manufacture, does not. Really with the op-amp and allowing of adjusting its gain one does not really need these. For the 8880 the analog input is the real easy part. The CPU interface is much more difficult, but really simple design. The only same pin out of the 8870 to 8880 is the input op-amp. After that all changes. I normally do away with the steering circuit for RC adjusting the attack/decay decode times. I do both in software and tie pins 16 17 together on 8870, 18 19 on 8880. This give instant decode/release time, but use software for the timing. As with any op-amp using a dif amp, as the 8870 8880 do, single ended or dif input can be done. Looks like you cut and pasted your posting, hi. Referred to figures not included. Oh well. 73, ron, n9ee/r Sorry I'm going to lose it here for a moment... What does any of this have to do with the original assertion that 3V P-t-P is always right for a CONTROLLER, Ron? Drop the 8870/8880 debate. The information WAS cut and pasted, because it was directly from the datasheet for both devices. I figured anyone could find them with a Google search and read them. But I was letting you drag me down the rabbit hole anyway. Let's go back to the topic I asked about. You said 3V P-t-P is what you shoot for. I still assert that 3V P-t-P is... wait for it... NOT ALWAYS RIGHT ON EVERY CONTROLLER! No one talking about the a controllers is hooking their rigs directly to the damn Mitel chip. Maybe 3V P-t-P is right for a CAT. I don't know (nor care). If the CONTROLLER MANUFACTURER says: 2V P-t-P or 3V P-t-P or 10V P-t-P... *** THAT is what they designed to and what should be used. *** What does the CAT manual say? If the performance sucks at that level, the manual is wrong, or the controller is built wrong. Either way, doesn't matter for sake of the comment I was correcting. --- So... The discussion went from why DTMF doesn't always decode on a CAT controller properly... To a bunch of folks saying they usually lower the level going into their CAT controllers... To me saying if the controller is done right, that's not necessary... To you talking about 3V P-t-P and it was worded in such a way as it sounded like you meant ALL controllers want 3V P-t-P... To me saying the way you worded it made it sound like ALL controllers want 3V P-t-P... and there's usually manufacturer recommendations for setting such things properly in each controller. To us discussing the details of the Mitel 8870 and 8880... To us debating the details of how to put an 8870 or 8880 into a circuit! HAHAHAHA... WHO CARES?! My point all the time has only been this: 1. Feed your controller with what the MANUFACTURER recommends. 2. If the controller doesn't decode well at the MANUFACTURER'S RECOMMENDATION, then they didn't design it right or they're clueless about their own decoder and their documentation is wrong. (NOT saying that about CAT... just saying it.) THAT'S ALL I was getting at. -- Maybe I should have just said... My S-Coms when set to their recommended levels, don't false or do any of that strange DTMF wonkyness! Nyah nyah nyah! Pt! Hahahahahaha... there. That better? More like a regular Internet mailing list, I suppose! (I was trying to avoid stooping to that level by instead pointing out that there are standards for levels published in good controller manuals. And those levels aren't ALWAYS 3V P-t-P!) The first way was much less likely to cause a mailing list flame-fest! Oh well. Flame away! I'll take Bob and Virgil's audio/analog engineering over a LOT of other things out there, any day of the week... So is the consensus that levels into a CAT have to be lower than what's recommended, or what? We never really got to the conclusion of that part of the discussion... what's causing all the DTMF flakiness for the original poster and other CAT owners that chimed in? I might find myself working on someone else's CAT someday (cough! haha... I won't buy one!) and need to know! (BIG GRIN) Nate WY0X
Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Nate, Chill out...take a pill, hi. The 3 V p-p is for the 8870/8880 internal op-amp level. Is it in stone? No, but found to be good level. This is not an input level to the circuit or IC, but is the internal op-amp output at pin 3 and what the internal parts of the IC is going to be decoding. How one obtains this is another design issue. The op-amp, as with any diff-amp, uses external resistors to set the gain. Simple op-amp design. Based on a given controller or other input if the gain needed is 2 then select the 2 resistor values correctly...if gain of 100 needed do the same. Again the 3 V p-p on pin 3 is a good measure to go for and again pin 3 is not an input from the outside world. I was responding to the post you sent to me and I made comments on it. Sorry you took it so hard. 73, ron, n9ee/r From: Nate Duehr [EMAIL PROTECTED] Date: 2008/03/30 Sun AM 01:37:15 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller Ron Wright wrote: Nate, I've been designing 8870s and 8880s in things for over 15 years. Good chip and it has lasted. Pin 3 is simply the output of the internal op-amp and using a feed back resistor to 2 and driving with another one can set the AC gain over a wide range. The gain is feedback/driving resistor unless you wish to drive the non-inv input. The 1/2 Vcc source, pin 4, was cleaver by Mitel to simply use with a single 5 V supply. As to the other gain pins it is best not to use these for some other manufactures of the chip do not provide them. California Micro Devices, probably one of the biggest manufacture, does not. Really with the op-amp and allowing of adjusting its gain one does not really need these. For the 8880 the analog input is the real easy part. The CPU interface is much more difficult, but really simple design. The only same pin out of the 8870 to 8880 is the input op-amp. After that all changes. I normally do away with the steering circuit for RC adjusting the attack/decay decode times. I do both in software and tie pins 16 17 together on 8870, 18 19 on 8880. This give instant decode/release time, but use software for the timing. As with any op-amp using a dif amp, as the 8870 8880 do, single ended or dif input can be done. Looks like you cut and pasted your posting, hi. Referred to figures not included. Oh well. 73, ron, n9ee/r Sorry I'm going to lose it here for a moment... What does any of this have to do with the original assertion that 3V P-t-P is always right for a CONTROLLER, Ron? Drop the 8870/8880 debate. The information WAS cut and pasted, because it was directly from the datasheet for both devices. I figured anyone could find them with a Google search and read them. But I was letting you drag me down the rabbit hole anyway. Let's go back to the topic I asked about. You said 3V P-t-P is what you shoot for. I still assert that 3V P-t-P is... wait for it... NOT ALWAYS RIGHT ON EVERY CONTROLLER! No one talking about the a controllers is hooking their rigs directly to the damn Mitel chip. Maybe 3V P-t-P is right for a CAT. I don't know (nor care). If the CONTROLLER MANUFACTURER says: 2V P-t-P or 3V P-t-P or 10V P-t-P... *** THAT is what they designed to and what should be used. *** What does the CAT manual say? If the performance sucks at that level, the manual is wrong, or the controller is built wrong. Either way, doesn't matter for sake of the comment I was correcting. --- So... The discussion went from why DTMF doesn't always decode on a CAT controller properly... To a bunch of folks saying they usually lower the level going into their CAT controllers... To me saying if the controller is done right, that's not necessary... To you talking about 3V P-t-P and it was worded in such a way as it sounded like you meant ALL controllers want 3V P-t-P... To me saying the way you worded it made it sound like ALL controllers want 3V P-t-P... and there's usually manufacturer recommendations for setting such things properly in each controller. To us discussing the details of the Mitel 8870 and 8880... To us debating the details of how to put an 8870 or 8880 into a circuit! HAHAHAHA... WHO CARES?! My point all the time has only been this: 1. Feed your controller with what the MANUFACTURER recommends. 2. If the controller doesn't decode well at the MANUFACTURER'S RECOMMENDATION, then they didn't design it right or they're clueless about their own decoder and their documentation is wrong. (NOT saying that about CAT... just saying it.) THAT'S ALL I was getting at. -- Maybe I should have just said... My S-Coms when set to their recommended levels, don't false or do any of that strange DTMF wonkyness! Nyah nyah nyah! Pt! Hahahahahaha... there. That better? More like a regular Internet mailing list, I suppose
Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
I once had the same problem with users voices falsing the DTMF decoder and causing the cover tone to be activated during voice conversations just like the original posters problem. I contacted the controller manufacturer, Peter at NHRC I think. He told me it is a comon problem with that decoder chip and to change a resistor to cause the time needed to reconize a valid digit to be longer. I dont remember the value or what resistor to change but it took care of the problem. I did a search for a data sheet for the decoder and the controller manufacturer followed the original circut to the letter so it wasn't their fault it falsed when set up properly and I took great care setting up levels with a scope so I know the problem was not on my end. Hope this helps someone. tom [Original Message] From: Ron Wright [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Date: 3/30/2008 9:37:14 AM Subject: Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller Nate, Chill out...take a pill, hi. The 3 V p-p is for the 8870/8880 internal op-amp level. Is it in stone? No, but found to be good level. This is not an input level to the circuit or IC, but is the internal op-amp output at pin 3 and what the internal parts of the IC is going to be decoding. How one obtains this is another design issue. The op-amp, as with any diff-amp, uses external resistors to set the gain. Simple op-amp design. Based on a given controller or other input if the gain needed is 2 then select the 2 resistor values correctly...if gain of 100 needed do the same. Again the 3 V p-p on pin 3 is a good measure to go for and again pin 3 is not an input from the outside world. I was responding to the post you sent to me and I made comments on it. Sorry you took it so hard. 73, ron, n9ee/r From: Nate Duehr [EMAIL PROTECTED] Date: 2008/03/30 Sun AM 01:37:15 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller Ron Wright wrote: Nate, I've been designing 8870s and 8880s in things for over 15 years. Good chip and it has lasted. Pin 3 is simply the output of the internal op-amp and using a feed back resistor to 2 and driving with another one can set the AC gain over a wide range. The gain is feedback/driving resistor unless you wish to drive the non-inv input. The 1/2 Vcc source, pin 4, was cleaver by Mitel to simply use with a single 5 V supply. As to the other gain pins it is best not to use these for some other manufactures of the chip do not provide them. California Micro Devices, probably one of the biggest manufacture, does not. Really with the op-amp and allowing of adjusting its gain one does not really need these. For the 8880 the analog input is the real easy part. The CPU interface is much more difficult, but really simple design. The only same pin out of the 8870 to 8880 is the input op-amp. After that all changes. I normally do away with the steering circuit for RC adjusting the attack/decay decode times. I do both in software and tie pins 16 17 together on 8870, 18 19 on 8880. This give instant decode/release time, but use software for the timing. As with any op-amp using a dif amp, as the 8870 8880 do, single ended or dif input can be done. Looks like you cut and pasted your posting, hi. Referred to figures not included. Oh well. 73, ron, n9ee/r Sorry I'm going to lose it here for a moment... What does any of this have to do with the original assertion that 3V P-t-P is always right for a CONTROLLER, Ron? Drop the 8870/8880 debate. The information WAS cut and pasted, because it was directly from the datasheet for both devices. I figured anyone could find them with a Google search and read them. But I was letting you drag me down the rabbit hole anyway. Let's go back to the topic I asked about. You said 3V P-t-P is what you shoot for. I still assert that 3V P-t-P is... wait for it... NOT ALWAYS RIGHT ON EVERY CONTROLLER! No one talking about the a controllers is hooking their rigs directly to the damn Mitel chip. Maybe 3V P-t-P is right for a CAT. I don't know (nor care). If the CONTROLLER MANUFACTURER says: 2V P-t-P or 3V P-t-P or 10V P-t-P... *** THAT is what they designed to and what should be used. *** What does the CAT manual say? If the performance sucks at that level, the manual is wrong, or the controller is built wrong. Either way, doesn't matter for sake of the comment I was correcting. --- So... The discussion went from why DTMF doesn't always decode on a CAT controller properly... To a bunch of folks saying they usually lower the level going into their CAT controllers... To me saying if the controller is done right, that's not necessary... To you talking about 3V P-t-P and it was worded in such a way as it sounded like you meant ALL controllers want 3V P
RE: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Tom, That solution is great when the user's DTMF pad holds the tone as long as the button is pressed. But, some radios and mobile mikes have DTMF pads that emit a very short tone burst regardless of how long the digit button is held. Lengthening the tone recognition time may prevent some users from accessing the features of the controller. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Thomas Oliver Sent: Sunday, March 30, 2008 9:34 AM To: Repeater-Builder@yahoogroups.com Subject: Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller I once had the same problem with users' voices falsing the DTMF decoder and causing the cover tone to be activated during voice conversations, just like the original poster's problem. I contacted the controller manufacturer, Peter at NHRC I think. He told me it is a common problem with that decoder chip and to change a resistor to cause the time needed to reconize a valid digit to be longer. I don't remember the value or what resistor to change, but it took care of the problem. I did a search for a data sheet for the decoder and the controller manufacturer followed the original circuit to the letter so it wasn't their fault. It falsed when set up properly, and I took great care setting up levels with a scope, so I know the problem was not on my end. Hope this helps someone. tom major snip
Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
At 3/28/2008 12:07, you wrote: If we were muting DTMF, we'd have had no idea why he was complaining. If DTMF mute is on tones are being muted, they must not be too bad. One system I maintain has ADMs set to a bit longer than the DTMF detect time, the DTMF mute delay is set to the same time, ~100 milliseconds. If anyone is having DTMF encoding problems, we'll hear it. Around here, not using DTMF muting is just asking for trouble. Bob NO6B
Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Nate, I've been designing 8870s and 8880s in things for over 15 years. Good chip and it has lasted. Pin 3 is simply the output of the internal op-amp and using a feed back resistor to 2 and driving with another one can set the AC gain over a wide range. The gain is feedback/driving resistor unless you wish to drive the non-inv input. The 1/2 Vcc source, pin 4, was cleaver by Mitel to simply use with a single 5 V supply. As to the other gain pins it is best not to use these for some other manufactures of the chip do not provide them. California Micro Devices, probably one of the biggest manufacture, does not. Really with the op-amp and allowing of adjusting its gain one does not really need these. For the 8880 the analog input is the real easy part. The CPU interface is much more difficult, but really simple design. The only same pin out of the 8870 to 8880 is the input op-amp. After that all changes. I normally do away with the steering circuit for RC adjusting the attack/decay decode times. I do both in software and tie pins 16 17 together on 8870, 18 19 on 8880. This give instant decode/release time, but use software for the timing. As with any op-amp using a dif amp, as the 8870 8880 do, single ended or dif input can be done. Looks like you cut and pasted your posting, hi. Referred to figures not included. Oh well. 73, ron, n9ee/r From: Nate Duehr [EMAIL PROTECTED] Date: 2008/03/28 Fri PM 08:09:36 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller Ron Wright wrote: The voltage levels on most DTMF decoders are set by the IC designer. On decoders like the 8880 and 8870 pin 3 is what the internal op-amp of the IC is producing and this parameter is determined by the IC designer. As with any IC one needs to supply the proper levels to the device to allow it to achieve what is needed. Pin 1 is the non-inverting op amp input, Pin 2 is the inverting op-amp input, and Pin 3 is Gain Select, described below. From the MT8870 datasheet: GS: Gain Select. Gives access to output of front end differential amplifier for connection of feedback resistor. The input arrangement of the MT8870D/MT8870D-1 provides a differential-input operational amplifier as well as a bias source (VRef) which is used to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for adjustment of gain. In a single-ended configuration, the input pins are connected as shown in Figure 10 with the op-amp connected for unity gain and VRef biasing the input at 1/2VDD. Figure 6 shows the differential configuration, which permits the adjustment of gain with the feedback resistor R5. Same pin-out on the 8880. You can build it as a single-ended input or a differential one, and mess with GS... depending on how you built your audio circuit... The input op-amp, has a decent amount of gain available in the op-amp itself, too... because it' meets the specs to pull a tone up from -31 dBm (dBm referenced to 1mV into a 600 ohm impedance input -- the typical telco reference for dBm) and won't fully reject tones until -37 dBm. These chips can hear DTMF tones that are incredibly low amplitude... on quiet circuits. The problem is... radios aren't quiet circuits. The published error rate at -31 dBm is 1 in 10,000 without background noises. They're very good decoders. But depending on how they're hooked up, generic statements like 3 V P-t-P aren't ALWAYS correct... unless the repeater controller is feeding the op-amp in the unity-gain single-ended configuration. Nate WY0X Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Same problem with the CAT200 controllers as well. The recommended procedure for adjusting the DTMF input level seems to call for a specific amount of audio on a test point. If the radio you use to adjust the CAT is on the low side (deviation), then it will be a bit over-sensitive and will mute occasionally on some voices. Lowering the setting just a bit will fix things for most users; the rest will need to adjust their own radio deviation levels. The CAT manuals have the adjustment procedure and test points well documented. Bob M. == --- Jim Brown [EMAIL PROTECTED] wrote: 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 home page. http://www.yahoo.com/r/hs
Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
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.
Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Tony, The reason why it falses on one of 3 controllers is probably not the controller, but what is feeding the controller and maybe slight differences in the adjustment. With varying audio characteristics from one repeater to another is probably the difference. 73, ron, n9ee/r From: Tony L. [EMAIL PROTECTED] Date: 2008/03/27 Thu PM 11:01:13 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller 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. Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
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
Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
The solution to allowing DTMF pass is if our first digit is a 5 it temp turns off the muting. We have all of our Echolink commands including the node accesses start with 5. We have little selective DTMF calling, but tell all who want to make sure their first digit is a 5. Simple and workable solution. The voltage levels on most DTMF decoders are set by the IC designer. On decoders like the 8880 and 8870 pin 3 is what the internal op-amp of the IC is producing and this parameter is determined by the IC designer. As with any IC one needs to supply the proper levels to the device to allow it to achieve what is needed. 73, ron, n9ee/r From: Nate Duehr [EMAIL PROTECTED] Date: 2008/03/28 Fri PM 02:07:43 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller 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 Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Ron Wright wrote: The voltage levels on most DTMF decoders are set by the IC designer. On decoders like the 8880 and 8870 pin 3 is what the internal op-amp of the IC is producing and this parameter is determined by the IC designer. As with any IC one needs to supply the proper levels to the device to allow it to achieve what is needed. Pin 1 is the non-inverting op amp input, Pin 2 is the inverting op-amp input, and Pin 3 is Gain Select, described below. From the MT8870 datasheet: GS: Gain Select. Gives access to output of front end differential amplifier for connection of feedback resistor. The input arrangement of the MT8870D/MT8870D-1 provides a differential-input operational amplifier as well as a bias source (VRef) which is used to bias the inputs at mid-rail. Provision is made for connection of a feedback resistor to the op-amp output (GS) for adjustment of gain. In a single-ended configuration, the input pins are connected as shown in Figure 10 with the op-amp connected for unity gain and VRef biasing the input at 1/2VDD. Figure 6 shows the differential configuration, which permits the adjustment of gain with the feedback resistor R5. Same pin-out on the 8880. You can build it as a single-ended input or a differential one, and mess with GS... depending on how you built your audio circuit... The input op-amp, has a decent amount of gain available in the op-amp itself, too... because it' meets the specs to pull a tone up from -31 dBm (dBm referenced to 1mV into a 600 ohm impedance input -- the typical telco reference for dBm) and won't fully reject tones until -37 dBm. These chips can hear DTMF tones that are incredibly low amplitude... on quiet circuits. The problem is... radios aren't quiet circuits. The published error rate at -31 dBm is 1 in 10,000 without background noises. They're very good decoders. But depending on how they're hooked up, generic statements like 3 V P-t-P aren't ALWAYS correct... unless the repeater controller is feeding the op-amp in the unity-gain single-ended configuration. Nate WY0X
RE: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller
Tony, Yes, but it requires throat surgery. Seriously, though, one repeater user in my area has a tendency to make a high-pitched eee sound when others might say um, and this will sometimes cause the controller to mute his voice just as it would a DTMF tone. Slightly reducing the DTMF decoder input gain seemed to eliminate the problem. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Tony L. Sent: Thursday, March 27, 2008 9:01 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller 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.
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.
