Well hell, I accidently sent the previous before I was finished: As I was saying, when I said:
> I could see the audio noise waveform change on > the scope at the output of the receiver. I can > easily find the ragged edge so I know it's this > adjustment. And you said: No, it's not... I have to ask: Then what is causing the squelch to break and why did it quit acting up when I tweaked it just a bit? It's obvisouly not aligned properly. I can turn it a tad CCW until the noise increases (possibly going into oscillation?) and breaks the squelch and then turn it back a hair CW until it stops. I can see the audio noise change when I hit the spot where it goes haywire. I have listened to this repeater for a few months with my trusty HTX-202 so I "earballed" it and left it until we can get to it. We will do the alignment again according to the manual soon. And you said: As I describe in my text, above 3.5KHz (service monitor) deviated test input, the MSR2000 receiver filters start to distort the audio. You can see it with a scope at the discriminator output. I say: Yep, you're perzactly right. However, on our second attemp to set the deviation back in March, we did have it looking pretty good up to 5K looking at the audio at the input of the controller. And it tracked pretty good up to about 3.5K. It held still for a couple months and then we had the Channel 11 spur that drove us crazy. It was so strong, I thought the repeater was broken. One day, there was noise getting through with the antenna disconnected.. During that episode we tweaked it again and probably messed it up. Final comment: Walt, WA4LDS and an engineer at Channel 4 here in Tucson noticed that when the picture changed on our local Fox channel, the repeater noise changed. He was instrumental in getting the Channel 11 engineer to tweak his transmiter and it is all better now. Thanks for the response. de WD7F John in Tucson ----- Original Message ----- From: "skipp025" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, July 27, 2004 10:35 AM Subject: [Repeater-Builder] Re: Deviation Limiting/Linearity Hi John, I'm here... > "WD7F - John in Tucson" <[EMAIL PROTECTED]> wrote: > Actually, I have two problems so it might > take two threads. (Long-winded too...no less) > It seems that if the deviation is not linear > when setting up IDC/Repeater Level and the > deviation limiting in the receiver. For the non Motorhead (Motorola) people, IDC is the channel element contained deviation control. The repeater in-out deviation will never be (track) linear on any repeater ever. There are at least three wild cards in your problem list. The first is the receiver bandwidth and any included (if used) de-emphasis circuit. The other wild cards are the transmitter (both the users radio and the repeater transmitter) pre-emphasis circuits. When these values get really wacked out, we run into an unbalanced tone level (dtmf is made from two tones) called twist. A big abuser is excessive or user radio over deviation. Most people don't realize how little audio is actually required for proper dtmf and sub-tone (PL) decoding. There are standards, but most out of the box user radios are set excessively hot. Specific to your MSR-2000 and Cat Controller. Know the receiver IF filters are tight. You will not get a good detected waveform with any voice audio deviated signal above 4KHz (without sub tone). So don't try... The statement just above is much of your problem. You also didn't say how you set the receiver on frequency. John, Again set the repeater up as described in my MSR2000 to external controller text, easily found at http://www.radiowrench.com/sonic Then follow what I write below (after a few more comments). > it has an adverse effect on the DTMF decoding > in the VA3TO interface that I use on Echolink. > IRLP and WIRES decoders work nearly flawlessly > with the same audio. This might tell you about a level and twist problem with at the dtmf decoders. A scope at the controller dtmf decoder chip input will give you the real answer. > I found that the 147 side of the keyboard would > not perform well for a lot of DTMF sources if > the deviation didn't track pretty closely from > 0 to 3 K or so. It's probably more than a deviation tracking problem. > We check it by putting in a 1K tone @ 1K deviation, > 2K deviation and 3K deviation, etc. There seems to > be a couple of schools of thought. Yep... > One, adjust IDC/Repeater level so it tracks 1:1, e.g., > 1=1, 2=2, 3=3, 4=4, etc. Close, but no cigar. You have to know the preformance of your receiver filter. As I describe in my text, above 3.5KHz (service monitor) deviated test input, the MSR2000 receiver filters start to distort the audio. You can see it with a scope at the discriminator output. Everyone setting up a receiver should know how that receiver preforms at X value input deviation. Your target value 1:1 deviation ratio for the the MSR is about 3KHz (set at one location) only, depending on the preformance of your receiver and how your external controller processes the audio. Be sure to "pull the TX PL tone reed" when checking these values. The 3KHz value is relative and "season to taste" based on your observations of the receiver to transmitter through-put (with no PL). I have seen and used values of 3.5 and up to 4KHz because some receivers filters were fairly linear at those test signal input - deviation levels. The key is to know the receiver preformance first, easily measure with a service monitor. You must also keep in mind that your repeater controller might not provide flat in-out audio. > The other is to check the deviation with no input > and adjust the deviation to compensate for noise > in the exciter, e.g., 1=1.2, 2=2.2, 3=3.2, etc. Yuck... > We have done it both ways. It's seems pretty tough > to get the linearity AND the deviation limiter in > the receiver aligned so that the deviaton is linear > and limited to about 5K and see a nice undistorted > audio waveform. As you describe both methods above, you will never see what you are trying to adjust for. You are shooting yourself in the foot. > we began to have what appeared to be an intermod or > spur problem which would break squelch and key the > repeater. > I put my adjusting tool on the L201 deviation > limiting adjustment in the receiver and cracked > it a little CW (higher deviation allowed) and > the problem went away. I bit my tongue when you wrote that you touched L201, you now need to follow the service manual instructions on how to get it back to where it should be. Before anything else, you now need to follow the Service Manual information to reset L201, second would then be to set the channel element to the best center frequency. I use a service monitor, set to you frequency minus the 10.7 (in most receivers) IF. If your receiver alignment is good, you then test and note (on paper), the discriminator audio output for various test tone input (deviated) levels. Also note the receiver output levels are different for classic 1KHz test tone vs other (in this case lower) voice audio range test tones of say 600 to 800Hz frequencies. I use 750Hz as another reference tone. Most human basic voice energy (frequencies) are actually much lower. Another also... Don't be fooled by the receiver sensitivity, modulated vs un-modulated (with test tones or voice audio). They will also be different. So will the receivers ability to track squelch closure as you move the test signal plus and minus your Freq-center. > I could see the audio noise waveform change on > the scope at the output of the receiver. I can > easily find the ragged edge so I know it's this > adjustment. No, it's not... > I even put the suspected R1 Audio card back in and > it works good. However, 147 won't work on K7IOUs > Kenwood (again) now.... Have you measure his radios deviation and dtmf tone twist? > because the deviation is no longer linear. Not the problem... you've got some homework to do. > By the way, the repeater still sounds great even > if the deviaton is not linear...so long as the > limiter is working. > Can any of you "gurus" with lots of experience give > me a hint on the alignment? The key phrase is "proper alignment". > Or should I throw away the VA3TO interface? If it works, keep it and use it. But you won't know if it's worth keeping until you've got everything set up right. > Skipp, I have read your alignment procedure a > hundred times, and it makes sense on paper, but > I'm not confident that I'm doing it right. I'm an Email away most of the time. In your and a few others cases, I'm a simple phone call away. > I would think that the deviation limiting would > not have an effect on the linearity, but it > seems that it does. > de WD7F > John in Tucson Everything changes everything and everything is a compromise. The trick is to measure and understand, then set any repeater system up for the best operational compromise. Your results will probably vary... cheers skipp skipp025 @ yahoo.com www.radiowrench.com 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/
