I'm going to comment on one part of this..the severe distortion. We had the same problem. First of all, I didn't use the voltage stamped on the exciter. It had 0.23 and I think we ended up using 0.19. Then, even though the repeater sounded pretty good, the audio wave form to the controller was severely distorted. It turned out it was the L201 that I was talking about in the deviation linearity problem I have. I finally remembered that I could NOT get the peak called for in the alignment of the limiting circuit. So when I remembered that and tweaked L201 a bit, the audio cleaned up. We then set the IDC and finally I set L201 so that it limited the deviation to approximately 5 K. That ain't by the book as per Skipp. Confession over.
As I said to Skipp, I will attempt to do the alignment again...after all, I AM much more experienced now... ;-) de WD7F John in Tucson ----- Original Message ----- From: "Army Curtis" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, July 27, 2004 2:58 PM Subject: [Repeater-Builder] MSR-2000 Deviation Question Well gang, I have a real interesting problem for you that's about to drive me nuts. I have a MSR-2000 repeater that I'm putting into the 2M ham band. This is one of the radios removed from service by the Ontario Provincial Police, so it is a Canadian Motorola VHF low split, originally transmitting at 141.xxx. Following the suggestions on the Repeater-Builder web site, I have converted it to a ham style controller (CAT-700). The radio tunes up per the book, with all meter readings very nominal, and it makes full power (100 watts) easily. Here's the issue... it will not deviate the transmitter more than about 2.7 KHz using a 1 KHz tone before it starts severely distorting. The problem appears to be in the exciter, which is a TLD9241A. There is a sticker on the exciter shelf that says 0.260 volts = 5 KHz deviation. Anytime I put more than about 0.140 volts into the exciter, it starts to distort. I am using an IFR-1200S to send and receive the 1KHz tone, and I'm looking at the wave form of the transmitted signal on the 1200S. I have verified the 1200S is clean by looking at its output on another service monitor, and it is very clean to beyond 6 KHz deviation. I have looked at the audio going into the exciter on a scope, and it is very clean to up around 0.400 volts, so I would say that the receiver, controller audio, and transmit audio up to the exciter input is not the problem. I tried changing the exciter to another identical board, same problem. I changed the channel element to a known good element, same problem. I have changed the audio input transistor on the exciter board (Q501), same problem. I have tried to adjust the IDC on the channel element. While it does change the deviation, it has no effect on the distortion. Here is some additional info I just ran down to the shop to check. Sending a 5 KHz deviation at 1 KHz signal into the IFR1200S from another service monitor shows no distortion, so no problem there. Putting an audio generator right on the audio input to the exciter shows the same issue, but here is where it gets interesting. Changing the audio frequency, I am seeing a definite pre-emphasis network somewhere in the exciter, as a tone of 1 KHz gives about 2.7 KHz deviation, but a tone of 3.2 KHz gives right at 5 KHz deviation, with NO distortion. So, here's my question. I always thought you set deviation on an FM transmitter using a 1 KHz tone, setting a maximum deviation of about 4.5 KHz. I can see with this exciter that doing that will result in much more than 5 KHz deviation at frequencies above 1 KHz. Yet the Motorola book calls for setting the deviation to 5 KHz using a 1 KHz tone. What am I missing here? Army - AE5P Nacogdoches, the oldest town in Texas Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
