Unitrunker Low Health On P25 Control Channel

[CanesFan95]

How come I have a strong perfect signal on a local P25 control channel, but with a dongle only get a health of like 25-30 out of 100. What settings can I try messing with? Thanks.

 

[CanesFan95]

Here's a screenshot of the scope on the control channel:

 

[Dog]

Have you checked "Drift Correct" or manually set the correction?

 

[CanesFan95]

I had the Correction manually set to -2.0 which always seems to work just right when you look at the scope display on DSD+. But I didn't have Drift Correct turned on. So I just tried turning it on, but it made no difference. And I should say sometimes I can get a health of 50-60, even though I have a local EDACS system that gets a perfect 100.

 

[SCPD]

You are not limited to increments of 1.0 ppm for the correction value. Follow the "Calibration Procedure" below. Get the Window value as close to zero as possible.

UniTrunker | Realtek RTL2832U

Once the Window value is near zero, play with the gain settings.

 

[CanesFan95]

Thanks. That has made a slight improvement. I've gotten the "Window" value down to about -1 or -2. But the Health only gets up to about 66 or 67 at best, and I've tried Gain settings everyewhere from 100 to 1,000. As long as the gain is about 300 or more, it no longer makes a difference and the Health maxes out at 66-67.

 

[ChrisABQ]

What antenna are you using?

 

[CanesFan95]

A Larsen NMO150/450/800 on a 2 x 2 foot peice of sheet metal in the attic of a 2-story apartment building.

 

[jim202]

I didn't see any information on where your located, or what system your trying to listen to.

Is there a chance this is a simulcast system? If so, it may take a directional antenna to help resolve your problem.

Simulcast trunking systems are poor for most scanners to function well. The multiple signals from the other towers can cause all sorts of signal distortion that is hard for you to hear or see without some expensive test equipment.

How well the trunking system is performing also depends on how well the radio techs originally set up the timing delays between the different towers. It also depends on how close you might be to an overlap zone between 2 of the towers. If your unlucky enough to live in one of those overlap zones, it will take a really good directional antenna to try and pick up the closest tower and try to null out the other tower.

 

[CanesFan95]

Hillsborough County, FL P25. I believe it is simulcast.

 

[Jay911]

Unitrunker and other decoders (PRO96COM etc) expect 40 trunk system 'messages' per second - IIRC, that is the standard number of messages on a Motorola P25 control channel. Certain manufacturers' (Harris, and perhaps others) systems only send 27, which is 67.5% of 40.

66-67 percent is near perfect decode on such systems.

 

[dave3825]

A Larsen NMO150/450/800 on a 2 x 2 foot peice of sheet metal in the attic of a 2-story apartment building.

Wish I had access to my apartments attic...

 

[slicerwizard]

The P25 standard specifies that single, dual or triple TSBK messages may be sent on the control channel.

single = 26.666... TSBKs/sec

dual = 33.333... TSBKs/sec

triple = 40 TSBKs/sec


Since Unitrunker knows whether it is decoding single, dual or triple TSBK control channel messages, it should know how to report signal health properly.

 

[SCPD]

Since Unitrunker knows whether it is decoding single, dual or triple TSBK control channel messages, it should know how to report signal health properly.

Andrew is absolutely correct. This is a very old defect in the program.

 

[CanesFan95]

Yes, I'm fairy sure it is a Harris system. Our county is upgrading from EDACS to P25. Both systems are currently running, but only a few users are on P25. Unitrunker shows "M/A-COM" as the MFID (Manufacturer's ID?). So, that would explain it! 66-67 is great then. But the Health does tend to wander around a lot and sometimes dips into the 30s and 40s. I can't seem to make it hold steady.

So let me ask this. How does Unitrunker "know" that the MFID is "M/A-COM"? As well as other stuff like "C4FM" and the callsign? Are those plain text strings of information that the system actually transmits on the control channel and tells you? And, what do the other things mean, like Channel Access "P2", RFSS "1", and LRA "1"?

Thanks.

 

[CanesFan95]

Interesting how when I compare waveforms from the dongle versus the scanner discriminator on the same control channel, the scanner has a smaller waveform than the dongle. I wonder if that means the dongle gives a stronger better decode?

 

[CanesFan95]

Unitrunker and other decoders (PRO96COM etc) expect 40 trunk system 'messages' per second - IIRC, that is the standard number of messages on a Motorola P25 control channel. Certain manufacturers' (Harris, and perhaps others) systems only send 27, which is 67.5% of 40.

66-67 percent is near perfect decode on such systems.

Does that mean Harris systems are a lower quality product?

 

[CanesFan95]

Wish I had access to my apartments attic...

Believe me, when it comes to RF, I wish I could afford to escape out of this apartment cell into a house in the worst way.

 

[princessthelus]

Does that mean Harris systems are a lower quality product?

If you have ever been in the field of broadcast engineering, yes

 

[CanesFan95]

If you have ever been in the field of broadcast engineering, yes

Well, that's a shame. If only the elected commissioners and sheriffs and procurement directors realized this. Plus whoever writes the specs on the request for bid proposals.