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  #21 (permalink)  
Old 11-14-2017, 1:12 PM
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Originally Posted by DaveNF2G View Post
Thanks, KA1RBI, for a useful answer.

I did some reading and the idea of incorrect voice modulation levels producing errors in the datastream appears plausible. The two main factors influencing the bit error rate are noise and Rayleigh fading. Excess audio can become noise particularly if the filters start "ringing". Granted that this "noise" would become part of the datastream as if it was legit, a datastream with a lot of crud encoded could still generate apparent data errors if the receiving software has trouble with it.

There are probably other mechanisms that can translate a poorly adjusted transmitting system into an increased BER at the receiver.
sorry, Dave. Analog signals get input to the speech vocoder and the speech vocoder outputs digital xMBE code words (at a rate of fifty codewords per second). The digital codewords are combined with sync, low speed data, and FEC (Forward Error Correction) and then the bits are interleaved (scrambled in order) for transmission. The key here is that the same FEC acts upon digital codewords, in exactly the same manner regardless of whether the original audio was (a) pristine, (b) overdriven / distorted, or even (c) encrypted.

In case (c) the Forward Error Correction (FEC) process operates identically with the way that the Forward Error Correction process operates in case (a). The content of the speech code words are completely irrelevant to the error-correcting layer; there's no such thing as a "problematic" code word - that is, a code word more or less likely to foil the FEC. The significant point is that noise in the analog audio medium is completely, 100% disassociated from noise in the digital, RF realm...

73

Max
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Old 11-14-2017, 4:27 PM
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Originally Posted by KA1RBI View Post
haha, looks like this one is a Harris, which would rule out LSM. There are some Harris experts out there but I'm not one of them...

Max
Don't sell yourself short. The ultimate (largest) difference between LSM and WCQPSK is pulse width. Harris narrowed the pulse width time to allow for greater time between pulses, thereby allowing greater variances in simulcast timing to address overlap destruction. The down-side is the pulse becomes more susceptible to error due to RF conditions. It takes less interfering conditions to create a error condition than that of LSM.

Basic physics, to gain something (timing) you have to give something (more susceptible to error)
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Old 11-14-2017, 4:32 PM
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Originally Posted by DaveNF2G View Post
Thanks, KA1RBI, for a useful answer.

I did some reading and the idea of incorrect voice modulation levels producing errors in the datastream appears plausible. The two main factors influencing the bit error rate are noise and Rayleigh fading. Excess audio can become noise particularly if the filters start "ringing". Granted that this "noise" would become part of the datastream as if it was legit, a datastream with a lot of crud encoded could still generate apparent data errors if the receiving software has trouble with it.

There are probably other mechanisms that can translate a poorly adjusted transmitting system into an increased BER at the receiver.
Toaster oven.

If you're not going to make any sense... neither will I...

Though your last line is accurate, though common sense and vague.

Last edited by ThePagerGeek; 11-14-2017 at 4:37 PM..
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Old 11-15-2017, 10:13 AM
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Ahh, the last refuge of the professional radio shop guy. "I know, but I'm not going to tell you." You guys are always playing I've Got A Secret like you're some kind of radio priesthood.

Explain, or don't, but drop the mysterious act.
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Old 11-15-2017, 10:16 AM
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Originally Posted by KA1RBI View Post
The significant point is that noise in the analog audio medium is completely, 100% disassociated from noise in the digital, RF realm...

73

Max
OK, I understand that better now.

We are still left with the original, still unexplained phenomenon.

Why are some transmissions error-free while others, originating from a particular location or type of user, are error-laden?
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Old 11-15-2017, 10:21 AM
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Originally Posted by ThePagerGeek View Post
... The ultimate (largest) difference between LSM and WCQPSK is pulse width....
From my POV there is another difference that's more significant still - described (modulo the usual obfuscation) in US patent 6,061,574. I've seen it in operation on a local P25P1/FDMA Moto LSM system...

Max
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Old 11-15-2017, 11:21 AM
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Originally Posted by DaveNF2G View Post
...like you're some kind of radio priesthood.
No one could ever top you in that regard.

I was explaining my statement of "toaster oven." It doesn't make sense. Neither did your overdriven statement.

As for the solution, there isn't enough information to determine what the issue is. That's why I choose NOT to guess and create a misleading solution. Perhaps I could play 20 questions to narrow it down to some LIKELY suspects, but "overdriven console" isn't even on the list to start with. Unfortunately, all of the likely causes are not fixable in the field in the end.

Lastly, the solution to a problem that CAN be corrected isn't a secret, it's either lack of information or brains. As Max pointed out, YOU proclaim to be the radio expert. (Your words.) I question your answer and you jump on me for pointing out how it is wrong.

"The only true wisdom is in knowing you know nothing"
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Old 11-15-2017, 11:23 AM
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Originally Posted by KA1RBI View Post
From my POV there is another difference that's more significant still - described (modulo the usual obfuscation) in US patent 6,061,574. I've seen it in operation on a local P25P1/FDMA Moto LSM system...

Max
Yeah. The "special sauce" that each manufacturer holds back.

In the end, each flavor of QPSK is compliant to the standard. The variations to a scanner could be interesting to look at.
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Old 11-16-2017, 9:37 AM
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TPG has a point about my rant. I do get frustrated with some radio shop techs who like to be Secret Squirrel, but to accuse any individual of such motivation, especially over typed communication without subtext, was rude of me. TPG's mode of expression appears to be very similar to mine in some ways. Someone at the other end of a computer connection cannot see the tongue shoved into the cheek, hear the amused tone of voice, or see the twinkle in the eye when something that reads as being mean or vicious is being said. I can't honestly say whether TPG is condescending, angry, teasing or any other thing. I probably took it wrong and I should know better.

I am sorry, TPG, for being so confrontational for no reason.
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