Phase 2

[Art Xbklyn]

I have SDRTrunk v0.6.0-beta-5.  Can't seem to natively decode P25-Phase 2 systems.  Is there something I need to add-in?

[jim...@gmail.com]

Need a tab bit more info. 

Do you see tuners in the tuner section? 

what system are you decoding? If its an encrypted system you can't decode it. 

Maybe a screenshot also?

[dave38...@gmail.com]

What system? According to Sdrtrunk wiki, Note: all APCO25 Phase 2 systems use an APCO25 Phase 1 control channel.   And unless something changed, try setting it up as phase 1.    

https://github.com/DSheirer/sdrtrunk/wiki/Playlist-Editor#apco25-phase-1-decoder-and-apco25-phase-2-trunked-systems:~:text=Note%3A%20all%20APCO25%20Phase%202%20systems%20use%20an%20APCO25%20Phase%201%20control%20channel.

[Art Xbklyn]

Hello all...it's the Morris County, NJ P25 system.....geez, hoping they didn't go full encryption but I haven't heard anything about that.  Using a HackRF so bandwidth is not an issue and there's audio output if I tune to a local conventional ham repeater.  Signal strength is -65dBm so no issue there either.  Couple of screen shots attached..thanks all.

[jim...@gmail.com]

Maybe to simple but what happens when you click on your Control channel?

[Art Xbklyn]

Nothing happens when I click on CC.....strange thing too is that I'm only seeing primary and secondary control channels, nothing stating "call" traffic.

I just loaded the Union County P25-phase 2 system and that's working. Still can't get Morris County to load.

[GTR8000]

There is no activity left on the UHF cell, you need to program the newer 700 cell instead.

[Art Xbklyn]

I loaded up the 700 system and I can see there's quite a bit of activity on it but still no voice....I also see a lot of "Fades" under channel status...not sure what that indicates.

[Art Xbklyn]

Starting to get some intermittent voice breakthroughs now on the 700 system so I assume the "Fade" status indicates a signal strength issue....kinda weird as there's a county site on the water tank literally up the road from me (possible that site is down but who knows).

[CT POLICE LIVE]

Yeah looks like your barely picking up the channel. Maybe check if all your antenna connections are tight. Maybe set your master gain to max 495 in tuner setting and see what happens.

[Art Xbklyn]

Yeah I have the RF gain to max but I have to keep the VGA gain kinda low because it introduces too much noise into the system. I think I see what's going on now....although the county site is very close to my place, ATT has a 700-LTE site that's even closer and it's doing a job on the front end of the HackRF which basically has no protection to adjacent band impairment.....noise floor is astronomical!  In the next couple of days I'll head upstairs to the attic and swap out the Hack with a spare RTL-SDR dongle and see if it gives me a bit more immunity.  This would have been simple if the county stayed on 470!  Thanks for helping me out.

[CT POLICE LIVE]

That's interesting, let us know if the RTL-SDR switch fixes it.

[Art Xbklyn]

I will for sure.....If I have to come up with a filtering scheme I'll post that as well. Back in a day or so....thanks again!

[CT POLICE LIVE]

Yeah maybe some type of filter or even a directional antenna would help, if the RTL-SDR swap doesn't help you that is.  This is what 770mhz looks like on Sdrtrunk without any interfere using RTL-SDR's.

[tv...@tvsjr.com]

Quit setting gain to "max" especially if you have significant noise issues. What matters is signal to noise - not raw signal. It's possible if not likely that backing the gain way down will actually substantially improve things. 

---

From: Art Xbklyn <arty...@gmail.com>
Sent: Saturday, November 11, 2023 19:31
To: sdrtrunk
Subject: Re: Phase 2

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[Art Xbklyn]

Nah...noise floor is too high at -50dBm...look at the screen shot.  I'd need at least -35dBm of signal for respectable S/I and that's just not in the cards unless I lived under the site. Two choices...raise gain or lower noise...next step is to lower noise.

[charley....@gmail.com]

Buy a custom filter.  Install a directional antenna aimed at a site close enough for a usable signal but as far as possible from the azimuth of the interfering LTE site.  Try a different SDR.  But I'd start by lowering the gains to a no-signal state then incrementally increasing to see if you can find a sweet spot - it's killing you in the higher 772 - 775 range.  But it may not be "in the cards" from your location.

[Art Xbklyn]

Yep....agree on all points. The irony is I was complicit in the construction of that AT&T site years ago...dang.

To be continued........

[Art Xbklyn]

Just swapped out the HackRF (Chinese clone) for the RTL-SDR.....still have pretty high noise floor but the RTL has far superior adjacent band rejection so the S/I is now very reasonable and calls are intelligible.  The TV amplifier is a negligible source of noise which is a relief.  I may have to go with a 2-SDR approach to cover both high and low bands...I have a low-band Airspy unit somewhere in the junk drawer that's begging to be used.  Screenshot attached. Thanks again for helping out.

[Art Xbklyn]

Does anyone understand why talk groups with empty alias columns break through even though just one talk group with a valid alias is enabled? Is there any way to prevent these unwanted TGs from showing up? It's a very busy county system and I'm only interested in my local district PD TG...thanks!

On Saturday, November 11, 2023 at 2:25:25 PM UTC-5 Art Xbklyn wrote:

[Art Xbklyn]

Just figured it out......make new TGs with the offending IDs as noted on the "Now Playing" screen and set them to mute.

[Art Xbklyn]

Good evening....I have my Airspy R2 running on SDRTrunk now.....is there a way to turn on Bias-T through SDRTrunk (I did notice the option for RTL-SDR dongles) or should I just keep the pre-amp powered up externally?  I haven't installed the pre-amp yet but I just want to make sure I understand the requirements as my SDR bank is in a remote attic location which is a pretty tough environment in which to make changes.  Thanks, Art.

[sdrtrunk]

Art, sdrtrunk doesn't yet allow you to control the airspy bias-T.  I think there's an open issue for adding that support.

Denny