P25 Error Count Question

[fmalloy]

With the BCD436HP I go into P25 Adjustment Mode to see the error count (Hold on a channel, press Vol, Func, Vol). I notice in a single transmission, the Err count value rises and falls, I'll see it go to 7, then drop down to 3 then up again, then down, etc. I would have assumed it was cumulative per transmission and would keep rising.

So it appears that it's taking time slice interval samples during the transmission and displaying the error count for each interval.

Is this true?

 

[kruser]

With the BCD436HP I go into P25 Adjustment Mode to see the error count (Hold on a channel, press Vol, Func, Vol). I notice in a single transmission, the Err count value rises and falls, I'll see it go to 7, then drop down to 3 then up again, then down, etc. I would have assumed it was cumulative per transmission and would keep rising.

So it appears that it's taking time slice interval samples during the transmission and displaying the error count for each interval.

Is this true?

It is a real time indication of the bad P25 frames. The higher the number, the more errors or frames not being decoded.
Zero is best of course.

If you set your P25 system to manual with a fixed level and are watching the P25 error rate counter, hit the function knob and rotate it one direction or the other, you will see your manual P25 setting increase or decrease. Watch the error rate counter and set your P25 setting to the value that produces the lowest error rate number when there is active talk occurring.

 

[fmalloy]

It is a real time indication of the bad P25 frames. The higher the number, the more errors or frames not being decoded.
Zero is best of course.

You still haven't cleared it up.

For example it displays "7" during the transmission - 7 bad frames? Ok. Then, in the same transmission, the display changes to "3". So what happened to the 7? Errors accumulate over time, the past ones don't "go away", unless it's displaying errors per frame, so each frame shows you how many errors in that one frame, and the next frame comes and the error count resets to zero.

Correct?

 

[kruser]

You still haven't cleared it up.

For example it displays "7" during the transmission - 7 bad frames? Ok. Then, in the same transmission, the display changes to "3". So what happened to the 7? Errors accumulate over time, the past ones don't "go away", unless it's displaying errors per frame, so each frame shows you how many errors in that one frame, and the next frame comes and the error count resets to zero.

Correct?

Again, it is a real time counter and conditions change in the signal (in real time of course) from simple things like the wind blowing a tree around, something causing a reflection of the signal etc.
That is why you are seeing it fluctuate as the real signal is also fluctuating in one fashion or another. Could also be caused by multipath distortion if it is a simulcast system.
Or it could be a business site coming on the air that is messing with the reception of your site slightly.
Regardless, if that number stays below 25 or so, you will usually decode enough P25 frames to where you will not hear errors by ear.

In your example, the change from 7 to 3 is just indicating that the signal "cleaned" up some.

I'm not sure if the error counter actually reads an entire P25 frame or just looks for bad data within each frame in which case it could be considered a cumulative counter (per frame) but the frames are so short, it acts more like a real time decode error counter.