P25RX P25 Phase 1/2/DMR Receiver With Bluetooth Audio Support

[btt]

Question: I was experimenting with various inside and outside antennas to test the effects on reception. When using a particular 800MHz band outside antenna (on an 800MHz trunking system), I was seeing four bars on the RF Sig Level meter, and -85 dBm, but the SIG light was not lit, and I got poor or no decoding. But when I changed to a different antenna, I got only one to one and a half signal bars, -103 dBm, but the SIG light was green, and I got good decoding. Could this be an overloading issue with the first antenna?

The LNA has an OIP3 of +40dBm, so it probably isn't an issue with that. It is possible that it is a nearby blocker. There is one person who reported experiencing this when in close proximity to some cell phone towers (where I assume the cell tower frequency was close to the control channel frequency). In that case, he reported that a 10dB attenuator helped. There are some blocking specs in the user manual.

[edit]
Another thing to look at in order to determine if you are receiving a good signal level, is 1) Look at the I/Q Symbol Plot. If there is a pattern with four distinct areas of symbols in the 4 quadrants of the plot, then you are receiving a good signal with symbol synchronization. 2) If the I/Q Plot looks ok, but you are not seeing a SIG led / TSBK/sec >0, then you should check to see that your reference frequency is correct. Is the reference frequency estimate showing in green/yellow/white in the Signal Insights tab? If it is showing red, then try to use the estimate to program your reference frequency. If the reference frequency is too far off, then the decoded symbols may be incorrect.

 

[btt]

Just got back from some testing of the updated AGC with the Bluetooth in a car. It could still be better. I'm going to continue working on the AGC, so you might want to hold off testing the new firmware.

 

[freqseeker]

I have had a chance to monitor a few systems (P25) and the decode sounds good.
I too have noticed that the stronger the signal the worse the decode. -72 dBm is flashing red with a count from 0 to 15 max. Weaker systems -95dBm have a decode blue to green. I have tried different antennas and my external ST2 with and without preamp without change. The ref frequency is very close to the sticker 39999875. This happens on the two strongest systems, one is 700 and the other is VHF.
I will have more time this weekend to tinker with it.

 

[btt]

I have had a chance to monitor a few systems (P25) and the decode sounds good.
I too have noticed that the stronger the signal the worse the decode. -72 dBm is flashing red with a count from 0 to 15 max. Weaker systems -95dBm have a decode blue to green. I have tried different antennas and my external ST2 with and without preamp without change. The ref frequency is very close to the sticker 39999875. This happens on the two strongest systems, one is 700 and the other is VHF.
I will have more time this weekend to tinker with it.

Thank you for posting the plots. This helps a *lot*. I'm not sure what is going on here. The signal looks great. 4 tight clusters looks like a great SNR with excellent sync. The reference freq is good, but TSBK/sec is not. You should be getting a better decode. I'll get back to you after thinking about this for a bit.

btw, The signal level is not the issue. I've probably mentioned it before in this thread, but it will demodulate at *much* higher levels in very bad signal environments. For example, it works excellent here with a -40dBm signal on top of a crowded hill packed with equipment across the spectrum using the supplied 800 MHz antenna and no external filters.

 

[freqseeker]

Here is a good example of a weaker signal with good decode.


Here is a strong VHF signal with poor decode.

 

[btt]

Here is a good example of a weaker signal with good decode.

Here is a strong VHF signal with poor decode.

Thank you. The UHF signal looks like simulcast CQPSK and the VHF look like it is probably C4FM. Can you try this when it is not decoding well?:

In the console:
$ logging 1

Do you see any output that shows messages like "ROT 90", "ROT 270" ?

 

[freqseeker]

I'm not very familiar with console entry, but when logging 1 is entered it shows logging 1 on the next line and then goes back to $. I don't see ROT 90 or ROT 270.

 

[btt]

I'm not very familiar with console entry, but when logging 1 is entered it shows logging 1 on the next line and then goes back to $. I don't see ROT 90 or ROT 270.

Thank you. That answers that question.

 

[btt]

Here is a good example of a weaker signal with good decode.
Here is a strong VHF signal with poor decode.

Could you also try manually adjusting the rotation and see if that helps with the poor decode?

In the console, try various phase offsets: (default is -0.1)

$ po 0.0
$ po 0.1
$ po 0.2
$ po -0.2

 

[icemantim8]

Hi Todd. Been following this most recent convo as I have a lot of clipping as well. This is the Colorado DTRS Simulcast site. I do not have line of sight to the tower. I am using the helical antenna on a metal surface. Suggestions? By the way, thank you for the excellent customer service. Love playing with this and getting to know it better.

 

[btt]

Hi Todd. Been following this most recent convo as I have a lot of clipping as well. This is the Colorado DTRS Simulcast site. I do not have line of sight to the tower. I am using the helical antenna on a metal surface. Suggestions? By the way, thank you for the excellent customer service. Love playing with this and getting to know it better.

For audio clipping, the issue is the audio AGC. I'm still working on improving that. With the version you are running now, try lowering the agc gain.

In the console:

$ agc 3.0 12000.0 0.05 ( the default gain is 3.5, $ agc 3.5 12000.0 0.05)

See the bottom of the page here for more information: P25RX Tips And Tricks

 

[boy7777777777]

I have found that using an antenna specific to vhf helps drastically. I have an 800mhz mobile and it will not decode a strong vhf signal very well at all. When I switch it to the vhf mobile antenna it works perfectly. The same goes for monitoring an 800mhz system. Use the 800mhz antenna. It took me a long time to figure this out. I have tried an all band scanner antenna and it does very poorly on any band.

 

[turnpike61]

I received my P25RX earlier in the week, and am quite impressed. Thanks for a great product. I have a few questions:

1. How do I correlate the information in the Talk Group Editor with the actual systems I am listening to? I have 5 P25 systems I am monitoring, and not all of them have grantee information showing up in the Description on the TG editor. I thought I could reconcile to SYS_ID, but that value appears to attach to more than one system. For instance, I have multiple systems that show up as SYS_ID 10, so that doesn't help.

2. The sensitivity on the 150-160MHz band (where the Virginia STARS system is) is very very poor, even on a 35 foot high diamond discone. Is there something else I need to do to copy P25 systems on VHF?

3. The device is sensitive to multiple iterations of the "Test Selected Frequencies" in the Search tab. I can do this sometimes only 2 or 3 times before the radio appears to lock up and I cannot tell if I am not seeing any P25 on a channel, or it has decided not to receive. I have to unplug from power and plug it back in to get it going again.

Thank you.

 

[freqseeker]

Could you also try manually adjusting the rotation and see if that helps with the poor decode?

In the console, try various phase offsets: (default is -0.1)

$ po 0.0
$ po 0.1
$ po 0.2
$ po -0.2

Tried all of the above several times changing antennas as well. No real change, default seemed best.
I will try taking it away from my house tomorrow to rule that out.
Thanks for the suggestions.

 

[freqseeker]

I want to emphasize that even though the unit is reporting poor decode the voice decode is actually very good. If it didn't report the signal quality I would not have known there was a problem (if there even is one).
This is the WSP 700 system that is multicast on the Federal VHF system I listed above as well as the original conventional P25 channels. I'm not a RF engineer but there could be an issue caused by the multicasting.
I am very impressed with this little unit.

 

[btt]

I made a couple of changes that may help with VHF frequencies. Can you guys that are having VHF issues test and see if there is an improvement?

Version 2020-10-09_2155

Thanks.

[edit]
Make that version 2020-10-09_2221

 

[btt]

1. How do I correlate the information in the Talk Group Editor with the actual systems I am listening to? I have 5 P25 systems I am monitoring, and not all of them have grantee information showing up in the Description on the TG editor. I thought I could reconcile to SYS_ID, but that value appears to attach to more than one system. For instance, I have multiple systems that show up as SYS_ID 10, so that doesn't help.

Sounds like I need to get the WACN to be part of the talk group records. I didn't expect that there would be multiple systems in the same area with the same SYS_ID. Thanks for the feedback on this.

Regarding the issue with the frequency test, I will see if I can reproduce it / fix it.

 

[freqseeker]

How do I correlate the information in the Talk Group Editor with the actual systems I am listening to? I have 5 P25 systems I am monitoring, and not all of them have grantee information showing up in the Description on the TG editor. I thought I could reconcile to SYS_ID, but that value appears to attach to more than one system. For instance, I have multiple systems that show up as SYS_ID 10, so that doesn't help.

You say you have multiple systems that show up as SYS_ID 10, are you sure they are not different sites of the same system? A system can have numerous sites that are part of the same system. Just curious.

 

[btt]

I made a couple of changes that may help with VHF frequencies. Can you guys that are having VHF issues test and see if there is an improvement?

Version 2020-10-09_2155
Make that version 2020-10-09_2221

I had to revert one of the changes. Please try 2020-10-09_2239 to see if VHF improves. Thanks.

 

[turnpike61]

HI BTT: My measurements current stable FW to 10-10.0651:
First, I confirmed good signal strength on all of these an another receiver. The antenna for that receiver is about 10 feet higher, but it let me know that I could copy the signal at reasonable strengths. Each of these is S9+ on a IC-706MKIIG, so I verified each was audible at good strength from my location. The P25RX was connected to a Diamond Discone at 35 feet, and I am at just short of 600 feet ASL up on a ridge. All of these are VA STARS control channels:

Frequency and signal on stable FW and new FW:
152.2025 -89 dbm/-93 dbm
151.070 -112dbm (no sig)/-117 dbm (note: S9+ on other receiver/antenna as well as SDS200 with whip on back)
151.3925 -77 dbm/-81 dbm
152.5475 -78 dbm/-83 dbm

As you can see, all lost signal, which wasn't good to begin with, with the new FW. I could decode with both, but signal strengths were lower.
Also, as a side note, the software does not ouput audio to PC when in FM mode, so I had to attach as separate amplified speaker to listen to the audio when monitoring the P25 CC directly.

Thanks.