x36 P25 Threshold? What is it doing?

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AZScanner

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I thought this question would be best on it's own thread so that it didn't get lost in all the other posts about these scanners. I spent a few minutes today playing with this setting after reading another poster say that setting theirs to Manual/10 helped their decoding ability. The 436 was working well for me already, but I wanted to see if changing this value helped or hurt things. It seems to have helped (so far, we'll see on the ride home when I leave work today). I haven't had one dropped or choppy transmission so far since setting it.

What I'm not sure of is why it seems to be helping. What is the scanner doing with this value when set? Maybe UPMan can explain this. I think if I had a better understanding of what the scanner does with this value, I would be able to make better use of the feature. The manual is pretty fuzzy on it other than telling me how to change it. There's really not much explanation of what it does.

Thanks,
-AZ
 

N0UDG

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Below is directly from Easier to Read BCD436/536 Digital Scanner Manual

“P25 Threshold Mode (Conventional Only) This mode sets the algorithm for P25 decode [1]. The default setting is Auto.

<="">Auto - Automatically sets the decode threshold based on received signal.
Manual - Allows you to manually set the threshold by using the P25 Threshold Level setting (below) or P25 Adjustment Mode.

Default - Sets the scanner to the default threshold of 8, Auto.

P25 Threshold Level (Conventional Only) Sets the RSSI value below which the scanner will not attempt to make P25 fine tune adjustments. If the signal is too low, RX reliability is not high enough to make P25 adjustments correctly [1]. The default setting is 8.
0 to 20”

This suggests to me that your P25 must not be trunked to get this to work, if I am reading this correctly.

I no longer live where I have a P25 Conventional site to monitor so I cannot try it out, but in the past when I could monitor a P25 Conventional Site my 396T and 996T could be set manually for the P25 Threshold Mode and it would stay put on that adjustment. Since I only had one P25 site to monitor it was near perfect in P25 decode performance!

However, when I got the 396XT no matter where I set the “P25 Threshold Mode” it would race up and down trying to decode and in so doing it did a poor job of it. Even the dispatch would frequently be garbled; something in several years of using the 396T I had never heard before.

So, I do not know if the new x36 radios are like the “T” models or the “XT” models of old. If they are like the “XT” then all you can do is set the “starting point” of their auto tuning efforts but it will NOT stay put.

However, if you have several different sites to monitor and most of us do then you would not want a static set P25 Threshold Mode setting, I would think.

I realize this is not to much help but I have never seen a good explanation of this either.
 

AZScanner

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Yeah, the manual really just tells you how to set this, not how it works. I learned by playing around with the scanner that it can be set for both trunked and conventional P25 systems. It's in the system options for conventional systems and it's a site level setting on trunked systems. The manual can be a bit confusing here, but the option exists on all flavors of P25 systems.

I'm currently taking a closer look at P25 adjustment mode in the manual. It looks like using that mode is how to determine the optimal value for this setting. The scanner is working well, but there are still a few burbles here and there that I'd like to clean up, so I'll be using this method to find the best value and lock it in on each site. I'd still like to know *why* setting this threshold manually works better than letting the scanner figure it out by itself on Auto, but my guess is that's something only the engineers and UPMan would know, and they are probably not allowed to share. Otherwise I think UPMan would have chimed in by now. ;)

-AZ
 

Dafe1er

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So, before changing these values with the P25 how was it sounding when it was at factory settings?

Was the transmissions really garbled or digital sounding? Were there times it just dropped out in the middle of a transmission? Was there times the channel came alive but had no audio?

I have been wondering what to do with the values and did not want to mess with them since the P25 system I monitor comes in loud and clear right out of the box.
 

AZScanner

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So, before changing these values with the P25 how was it sounding when it was at factory settings?

Was the transmissions really garbled or digital sounding? Were there times it just dropped out in the middle of a transmission? Was there times the channel came alive but had no audio?

I have been wondering what to do with the values and did not want to mess with them since the P25 system I monitor comes in loud and clear right out of the box.
No, nothing like that. It was really just about perfect, but every once in a while the scanner would cut out for a brief moment. I'd say it's 95% good to go on this system using the factory default settings of Auto and 8. I'm just trying to play around and get that last 5%. Right now I'd say I've gained another 3% or so in quality, so 97% out of the 100% I'm trying to achieve. For folks in your situation where the scanner works perfectly as-is, then I say don't fix what isn't broken. For others who are having an occasional hiccup or two, and especially those reporting a lot of problems, I really recommend using the P25 adjustment mode to lock down the optimal settings. It can only help.

-AZ
 

Dafe1er

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No, nothing like that. It was really just about perfect, but every once in a while the scanner would cut out for a brief moment. I'd say it's 95% good to go on this system using the factory default settings of Auto and 8. I'm just trying to play around and get that last 5%. Right now I'd say I've gained another 3% or so in quality, so 97% out of the 100% I'm trying to achieve. For folks in your situation where the scanner works perfectly as-is, then I say don't fix what isn't broken. For others who are having an occasional hiccup or two, and especially those reporting a lot of problems, I really recommend using the P25 adjustment mode to lock down the optimal settings. It can only help.

-AZ
Thank you. This is what I was looking for information wise. I will leave it as is unless something arises.
 

AZScanner

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x36 P25 adjustment mode demystified

Okay, after playing around extensively with this feature, I've found that the manual is a bit misleading as to how this works. After reading the manual I thought that the scanner would automatically determine the best value for me, but after trying it out, I found that it's a bit more of a manual process to find the "sweet spot" for each particular system/site. However, it's really easy and the results are quite good (for me at least). I went from an occasional hiccup on our DTRS to rock solid decodes at least 99% of the time. YMMV of course, but for anyone having trouble decoding P25 on these units, this is worth a try.

Before you begin: (This walkthrough assumes you are adjusting sites or channels in a favorites list, but it should work for the full database as well.) You will need to edit your FL and set your site/channel's P25 threshold mode to Manual. Otherwise the method described in the manual to lock in the setting won't work. Here's how you do that (for trunked systems):

Menu>Manage Favorites>Review/Edit System>(scroll to select system)>Edit Site>(Select Site)>P25 Threshold Mode>Manual.

Conventional P25 systems are similar to this, but you would edit the channel instead of the site.

Now you're ready to begin. Again, this is for trunked systems, but conventional systems work similarly to this. Just substitute "channel" for "site" in the steps below:

1. Hold on the site that you want to adjust (Func+Dept, then scroll to select).

2. Enter P25 adjustment mode: Press Func+Vol on the 536 or Vol, then Func+Vol on the 436. You'll see ERR:--- 8 MAN on the display.

3. Press and hold the Func button and turn the scroll knob to the left until the display looks like: ERR:--- 2 MAN. You probably won't receive any P25 at this point. That's fine, we're going to fix that in the next step.

4. SLOWLY turn the scroll knob to the right, one stop at a time, until you start hearing P25 traffic again. Now you should see stuff like this "ERR 42 4 MAN" or similar and the scanner will sound pretty bad. No worries. Keep going until the error value reads 0 consistently whenever there's a transmission.

5. Once you're getting consistently error free decodes you can leave it where it ended up or go up one more notch just as a precaution - this is what I did.

6. Press Func+Vol to exit the adjustment mode.

That's it! Repeat steps 1-6 for each site or channel you want to adjust. Easy as 1-2-3.

I already loved this scanner when I got it, but I am REALLY loving it now. Give this a try, you'll be glad you did.

-AZ
 

redburgundy

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Do you expect the P25 threshold value to have any impact on non-P25 systems?
For two Motorola trunked systems I tried it with, I can't find a value where the ERR is consistently zero, but setting the threshold value to 10 rather than 8 seems to make the performance better
 

whsbuss

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Do you expect the P25 threshold value to have any impact on non-P25 systems?
For two Motorola trunked systems I tried it with, I can't find a value where the ERR is consistently zero, but setting the threshold value to 10 rather than 8 seems to make the performance better
It should improve digital transmissions.
 

policefreak

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redburgundy said:
Do you expect the P25 threshold value to have any impact on non-P25 systems?
For two Motorola trunked systems I tried it with, I can't find a value where the ERR is consistently zero, but setting the threshold value to 10 rather than 8 seems to make the performance better
Ive tried it on 2 Mot Smartzone Type 2 systems, and both times 8 seems to be the optimum setting. The ERR rates are in the 15-30 avg for both. The audio sounds ok, not choppy but each time I notice the transmissions cut out early and cut in late. May have to make a video. I think its some sort of a timing issue with the digital processor. Just like how phase 2 audio slows down to compensate for any error in transmission, I think the Common Air Interface P25 is being processed too quickly. Just a guess.
 
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