SNACC analog system and digital noise on transmissions

[br0adband]

Anyone else note that even in spite of the main SNACC system being an analog Motorola Type II trunking system (this has nothing to do with SNACC's new P25 Phase I system, mind you) there appears to be a lot of digital noise happening these days on the transmissions, especially with a lot of the North Las Vegas Police talkgroups? It's been steadily getting worse as time passes, in my opinion. I noticed it a few months back on random occasions but nowadays it's all over the place with the NLVPD traffic, sometimes it's so bad that the Dispatchers ends up requesting the units to repeat themselves not once but two and even three times before things come through clearly.

I noticed it reached pretty bad this morning because of a shooting that took place over on Green Valley Parkway - was just monitoring just a few moments ago when some of the PD units were trying to relay info to Dispatch about witness reports on the perps as well as the vehicle(s) that left the scene. Even caught a lot of the noise in traffic from one of the Clark County EMS units calling in to a local hospital asking for a Doctor to authorize them to call an order for them to stop attempts to revive the victim of the shooting (multiple GSW to the face and body) because they were unsuccessful.

Now hearing it again as an NLVPD unit calling in more info and a phone number, the digital noise is so prevalent on the NLVPD talkgroups I have to wonder what's going on with their entire side of SNACC. I'm guessing they're using some digital link, perhaps some type of VoIP links from their EOC to sites, I don't know, but it sure as hell ain't a pure analog system anymore.

Just for the record: I'm not talking about typical analog noise like static and generally bad signal quality because of location or something else, I mean the audio quality of the transmissions from mobile units - it rarely ever happens with Dispatch transmissions but it's there as well to smaller degrees - exhibiting the telltale 'noise' caused by the aliasing when the analog audio is converted to the digital format by the codec in use (typically some IMBE or similar algorithm at work).

I can post samples I suppose of what I mean but I think most folks understand what I'm talking about. It happens primarily on the NLVPD talkgroups but now it's becoming noticed on the Clark County EMS talkgroups, the McCarran airport traffic, and some of the LV Water District talkgroups as well. It doesn't appear to be related to the P25 system at all so, I have to wonder what changes have been put into action on the SNACC analog system during the changeover and upgrade to the P25 which is underway.

Ah well, something I've taken note of and wondered if anyone else has noticed it recently.

 

[Junior1970]

Motorola upgrades???

First,
What kind of scanner are you listening to?
Second,
Is it digital noise or do the voices seem garbled but intelligible?

In Utah when UCAN (now UCA) changed all their site controllers to a digital interface, primarily because the original parts for those analog site controllers in the Type II system became obsolete, anything patched from analog of VHF sources sounded that way. Mostly officers talking to dispatch. Over time it improved but when traveling through Central Utah and are listening to,say, a UHP talkgroup it will still sound this way because of the analog patch from VHF.

I listen on a Pro 96 and 2096 setup but rarely is anything on the UCA Type II system here in P25 Phase I but there is some......

 

[br0adband]

RTL sticks with Unitrunker handling the tuning/control duties, output to my laptop's sound chip so nothing special. If I tune the individual frequencies using SDR# manually and just sit on one till a transmission happens along (since it's a trunked system) it's the same audio - I did that test thinking that perhaps Unitrunker was adding or modifying the audio in some manner but it doesn't.

The voices are intelligible most of the time but on occasion it just turns to absolute crap and the issue isn't on my end: a few days ago I heard a call from an EMS unit into a hospital (like the one earlier today) and the EMS side went completely haywire in the manner in which digital noise does where everything just begins to sound like a heterodyne on top of itself multiplied by itself a few times and the signal just because this utterly unreadable traffic. After the EMS unit keyed down the hospital ER desk radioed back their transmission was entirely unreadable so the EMS unit came back and the EMT himself even stated words to the effect that he knew something about the system moving to a digital nature of some kind (apparently he'd been notified they might have some intermittent transmission problems).

Here's a 2 minute 18 second section of various samples (5,533,887 byte 320 Kbps MP3 file):

https://drive.google.com/file/d/0Bz-YZ7AFTnT8WUxWV1dRRERBY00/view?usp=sharing

Upon listening you should be able to discern the telltale aliasing happening on most of the audio, especially if there's background noise captured in the transmission - it gives the whole thing that fuzzy kind of quality, especially in the section with the last 20 seconds or so. There's traffic from a variety of agencies in this sample file, NLVPD, Henderson PD, Clark County Fire/EMS, and one or two others so it's not just one particular agency exhibiting this trait in their transmissions.

Didn't get a chance to capture anything really severe that caused issues with Dispatch not being able to read things and asking for a repeat but it does happen quite often even so.

Just one of those things, I might be older now with not as much high end response in my hearing but that digital aliasing noise jumps right out to me. And yes, it's most likely some digital hardware added into the signal path to transfer things around since we're all moving to digital sooner or later in one method or another.

 

[saburton]

I'm not an expert in the matter, but I believe that the digital noise that you are hearing is the conversion from the new SNACC P25 system to the analog side. As a user of the system, I know we are now using the digital side exclusively, mostly on the simulcast tower. I hear a lot more unreadable transmissions than before we switched, more so when there is a lot of traffic across the system. I have been using unitrunker to monitor the P25 simulcast on 853.9000 control channel. There is a lot of NLVPD, Henderson PD, CCSDPD, and LVVWD talkgroups on there. And since it is mostly showing each user's radio ID, I'm guessing that most users are just using the digital side as well.
Hopefully this gives you a little insight into a possible reason for what you are hearing.

 

[Junior1970]

Pretty much what I was saying.

Many of the conversations still sound like that today on some of the most rural patches of the Utah system. The urban areas not so much.

 

[br0adband]

Yah, that's appears to be the case in this situation, the audio is being patched over from the digital side so that would cause such issues. I can't monitor both systems at the same time to see if there's crossover - well I could just tune one stick to the 854.7125 CC and the other to the 853.9000 CC and watch for simultaneous activity but I guess I don't need to go that far.

It'll be interesting to see how all this plays out over the next year or so as the P25 switchover kicks into high gear.

 

[br0adband]

Been monitoring a lot today and I swear, that noise is just getting worse by the day - multiple times in the past hour (since about 8:30pm on Friday to the time of this post) the transmissions are flat out unreadable on my end and Dispatch on various talkgroups is asking for units to keep repeating over and over and not a whole lot is actually making it through.

Sure hope those radio system techs realize this is happening, I'm sure they do but it ain't pretty so far.