TRX-1: P25 Digital trunking - fine tuning

[jimjhones]

Hi guys,
I'm doing my 1st steps with P25 digital trunking using the TRX-1 and I will be grateful for some help and clarifications:

After scanning the relevant range I built a list of the Control channel frequencies and their Voice channels and set them up in sites.
When I'm running the scanner it does lock from time to time and decode the signal - hance the frequencies should be ok.
However, reception is far from being optimal.
I rad some posts regarding the ADC, DAC and DSP level and it does change things a little.

1. I'm trying to figure out how to verify that I'm in the best settings for each one of them. Is there something like an info/debug log that can tell me what are the levels of reception?
if not - I thought of getting this info from the display:
Top row - from left to right there is the signal bar, T for Trunking and D2 and at the bottom I have the VC when it decodes.
Which will be effected by what value? (I mean i.e. does lowering the ADC will lower the signal bar? the detection of trunking? I', not sure I'm clear here but the idea is to get some feedback of what levels are correct and what should be changed)
2. On the manual (If I recall correct) it says that ADC DAC and DSP goes hand in hand. I'm missing something here since I thought that ADC is responsible for the incoming level to the digital converter. then it goes to the DSP (Still unsure what does DSP level adapt does...) and DAC is responsible of the level of voice "creation". As I understand - I can be OK with ADC - feeding the DSP with the right level and then play all the way with DAC and change how it sounds but it doesn't have to go in conjunction to the input level of the ADC.
Doesn't match what the manual say do what am I missing here ?
3. When running the scanner on the sites list it starts without any detection and when time goes it gets better. as if it fine-tunes it-self or something a like.
I thought that these are missing frequencies but after a couple of sessions in which Ive added missing frequencies I got t the point in which there are no new freq. but it still behaves the same. Any reason for that?

Any tips and ideas will be appreciated
Thanks
Jim

 

[tvengr]

Welcome to the Radio Reference forums! If you are missing transmissions, it may be due to simulcast distortion. It may also be that they are encrypted. It would help to know your city, county, and state and which agencies and systems you are monitoring. Also, let us know which sites on trunked systems you are scanning. Please attach your TRX-1 EZ Scan file so we can take a look at it. Click on Attach files and open the file.

 

[RaleighGuy]

After scanning the relevant range I built a list of the Control channel frequencies and their Voice channels and set them up in sites.

I rad some posts regarding the ADC, DAC and DSP level and it does change things a little.

1. You do NOT need to put in the voice channels, only control channels. The CC tells the scanner where to go for the voice traffic.

2. Unless you know what you are doing DO NOT change the ADC, DAC or DSP Level settings you can mess up the reception even worse than it is. The majority of the time these settings should be left as default and systems will work fine.

3. Since you don't list the systems you are monitoring, I agree with @tvengr and think your issue is simulcast. Simulcast systems only work well on SDS scanners and certain other receivers (SDS, Unication Pagers, etc). The TRX scanners may work depending on your location, but are very bad at receiving simulcast systems. At home my TRX & other WS scanners work, but a half a mile away I get nothing.

 

[jimjhones]

1. You do NOT need to put in the voice channels, only control channels. The CC tells the scanner where to go for the voice traffic.

2. Unless you know what you are doing DO NOT change the ADC, DAC or DSP Level settings you can mess up the reception even worse than it is. The majority of the time these settings should be left as default and systems will work fine.

3. Since you don't list the systems you are monitoring, I agree with @tvengr and think your issue is simulcast. Simulcast systems only work well on SDS scanners and certain other receivers (SDS, Unication Pagers, etc). The TRX scanners may work depending on your location, but are very bad at receiving simulcast systems. At home my TRX & other WS scanners work, but a half a mile away I get nothing.

Hi, Thank you for the reply.

I had doubts if adding the voice channels will make it work smoother but it will be much easier for me to put only CC. Thanks for that info.

As for the levels, to begin with - I saved the original state and have no problem loading it if needed, but I did make some progress with changing these values. I have the feeling that the fine tunning is where I'm stuck.
- It is strange because (as i mentioned) It takes 10 to 20 minutes for conversations to appear...

I'm sorry I cannot be more specific with systems, channels and such. I'm working is sales and most of the time I'm traveling around so every couple of days I'm in a different state - Mostly in the U.S but some times in Europe. It's very challenging to learn to setup the scanner in this scenario but it's fun

 

[tvengr]

One thing to remember is that trunking tables for a site may be set to Standard only if all of the frequencies are all 800 MHz. If any frequencies in a site are VHF, UHF, or 700 MHz, trunking tables must be set to Auto Fill.

 

[RaleighGuy]

- It is strange because (as i mentioned) It takes 10 to 20 minutes for conversations to appear...

Find it hard to believe a conversation doesn't appear on the scanner for "10 to 20 minutes" but then I've never been in Europe, maybe things work differently there.

 

[Ubbe]

I'm missing something here since I thought that ADC is responsible for the incoming level to the digital converter. then it goes to the DSP (Still unsure what does DSP level adapt does...) and DAC is responsible of the level of voice "creation". As I understand - I can be OK with ADC - feeding the DSP with the right level and then play all the way with DAC and change how it sounds but it doesn't have to go in conjunction to the input level of the ADC.

You have a full understanding of how it works. DAC has nothing to do with decode and only sets the voice level in relation to analog channels so it can be more equal in volume level.

Whistler isn't really telling us what DSP adaption level actually does and we have no way to know if we are improving the decode quality when changing the value as there's no bit error display to guide us as Uniden has in their scanners.

The process then has to be to adjust DSP in one direction until the decode goes worse and then adjust in the other direction to improve it again and when it goes equally bad as in the other direction you set the value to the middle of those two worse values. Then fine tune with ADC.

If things change after 10-20 minutes it can only be that the frequency are drifting, there's no auto adjusting function that analyze the signal. But for simulcast systems, where several signals from different towers mix, the condition of their relation in signal strength can vary over time, like those 10-20 minutes, and can go in waves back and forth.

For simulcast reception it seems that Whistler scanners are extremely sensitive to be exact on the frequency to make it work as good as possible. As a user we have no means of adjusting and calibrating the reference oscillator in the scanner, it's done be service software in both Uniden and Whistler scanners. My TRX-2 came out of the box slightly more than 1KHz off in frequency in the 400MHz band, that will be more than 2KHz in the 800MHz band. My Uniden BCD536 where 1KHz off in the other direction but neither Uniden nor Whistler say anything about how accurate their scanners are. 1KHz equals to a 2ppm error.

/Ubbe

 

[jimjhones]

You have a full understanding of how it works. DAC has nothing to do with decode and only sets the voice level in relation to analog channels so it can be more equal in volume level.

Whistler isn't really telling us what DSP adaption level actually does and we have no way to know if we are improving the decode quality when changing the value as there's no bit error display to guide us as Uniden has in their scanners.

The process then has to be to adjust DSP in one direction until the decode goes worse and then adjust in the other direction to improve it again and when it goes equally bad as in the other direction you set the value to the middle of those two worse values. Then fine tune with ADC.

If things change after 10-20 minutes it can only be that the frequency are drifting, there's no auto adjusting function that analyze the signal. But for simulcast systems, where several signals from different towers mix, the condition of their relation in signal strength can vary over time, like those 10-20 minutes, and can go in waves back and forth.

For simulcast reception it seems that Whistler scanners are extremely sensitive to be exact on the frequency to make it work as good as possible. As a user we have no means of adjusting and calibrating the reference oscillator in the scanner, it's done be service software in both Uniden and Whistler scanners. My TRX-2 came out of the box slightly more than 1KHz off in frequency in the 400MHz band, that will be more than 2KHz in the 800MHz band. My Uniden BCD536 where 1KHz off in the other direction but neither Uniden nor Whistler say anything about how accurate their scanners are. 1KHz equals to a 2ppm error.

/Ubbe

Thank you very much for the detailed answer. At least I know I'm on the right spot when it comes to understanding the system

You mentioned at the end of your things that you got the scanners a little bit of tune. How did you measured it? (I mean - how did you discover that)
I saw that the Zeromatic had something to do with it but only during scan? Do you have some knowledge regarding ?

thanks again
Jim