LAPD Digital Noise

[tomasG]

I am posting here because my question is specific to LAPD.

I have a Uniden 785D with a APCO P25 card. It works very well except that when scanning LAPD it will stop on a channel with a burst of digital noise. Do LAPD cars send digital data from their MDT's on the same frequency? Is that the burst I am hearing? Do the newer 996's have this burst too? I know that LAPD uses NAC but the 785D doesn't do that. Do they also use PL tones? I've heard that on some systems do that.

 

[WayneH]

My understanding is the bursts are for OTACS/OTACR. Basically what the data messages do is when a radio is within range of that repeater the radio will reassign it's first 16 channels to that division (or however they divide things up). Nothing is added (or essentially programmed) in the radio; it just reorganizes what's already there.

A local will have to confirm if you can block out the data messages. Since they include a NAC I don't think you can. With P25 there is no PL as the NAC takes its place.

 

[tomasG]

WOW. A self-associating system. But it must get confusing to think that if you are on channel 3 you are talking to base when channel 3 might now be SWAT. I wonder if it more like a voting system.

 

[WayneH]

WOW. A self-associating system. But it must get confusing to think that if you are on channel 3 you are talking to base when channel 3 might now be SWAT. I wonder if it more like a voting system.

It's a voted system also. But the first 16 channels are typically dispatch and TAC channels so there's no serious worry about being on the wrong channel.

 

[tomasG]

I read up on OTAC and noted that LAPD's implementation of it is unique. Just as you said, as units move around they self-associate with the repeater in that area. Most of their dispatch channels are on each mountaintop, so they aren't really reassigning the first 16 chennels as much as they are pre-voting. I heard a wild chase that went all the way to San Diego and LAPD units held the repeater much of the way. They wouldn't hand it off to Highway Patrol.

 

[pepsima1]

Hello: I have the Uniden BCD396XT and the BCD996XT and I seem that to ever have this problem. Before I entered in the NAC for each frequency I didnt have that problem. I also added the NAC when I got these scanners and they are great. No problems.

 

[tomasG]

I am on a budget and bought from eBay. In hindsight I should have waited for another paycheck, but I didn't know of OTAC or whatever it is.