BC996XT-Multipath Interference on P25 Simulcast Systems

[Ben96cal]

Many of us in the San Francisco Bay area are absolutely fed up. We have had a new P25 Simulcast system in Oakland come online a few months ago and unless you are very close +- 5 miles the scanner is not decoding the traffic. You can have FULL bars but all you'll get a either zero traffic or you'll hear a bunch of jibberish. I've compressed the issue into this post from several posts of the thread going on in our forum.


BC's do NOT WORK with p25 simulcast unless you are line of sight with one site only, or close enough to one site that it over powers the other site and then your BC will pick up only that site and will not receive interference from the other sites.

This problem is caused by time delay of the signals your scanner is receiving from the multiple sites, it's like a simplex channel and 2 or 3 people try to transmit at the same time.

A simulcast system relies on VERY tight time synchronization and the mobiles are designed and programed to handle system time sync.

Unfortunately the reception problems with Uniden scanners are not caused by any temporary issues with the system itself. They are caused by the format of the digital signal. Uniden scanners were designed to decode C4FM modulation used on Motorola Smartnet and Smartzone systems. The new Oakland system uses CQPSK modulation, also known as Linear Simulcast Modulation (LSM), which is supposed to be compatible with C4FM, but the scanners do not handle it as well. As I mentioned before it is possible use a Uniden scanner to monitor the system if you are receiving a signal from only one site, but if you are in range of multiple transmitters, the multipath interference renders the scanner fairly useless.Sm example of this can be found in the below Youtube link.. This is not a new issue as MANY people have had the same issue back east and in the midwest on large state simulcast systems.

I've updated my 996 with firmware 1.06.

Youtube
P25 Simulcast Distortion - YouTube


The city of Oakland still has their Edacs system up and running and we all have zero issues with that system so it's not our setup.

Uniden please look into and resolve this issue asap. It's ridiculous that we bought a $500 scanner that isn't doing what it's supposed to on P25.

 

[cb225662]

Simulcast Issues

I totally agree with you! My 996xt is useless on these systems. I would probably advise people that live in a area that has one of these systems not to buy radio until they fix the problem with the radio's I also did the update, It did not do anything to help the the problem that I can see..Also messed around with directional antenna to no ad-vale

 

[ofd8001]

Here in Louisville we have a similar issue with simulcast transmitters.

I have been able to improve the situation through tinkering with the P25 settings. It was trial and error but I eventually found a combination of settings that reduces the garble.

Another possible solution is to enable the attenuation setting to dampen the reception on the scanner.

Hopefully this is a problem that Uniden (and other scanner manufacturers) can deal with eventually. There's been several posts on this topic in other forums.

I'm a fire chief and thus have a radio on the new system. There's a world of difference in the sound between a scanner and the radio, (but there's also a world of difference between the cost of the two).

 

[Ben96cal]

re:

Here in Louisville we have a similar issue with simulcast transmitters.

I have been able to improve the situation through tinkering with the P25 settings. It was trial and error but I eventually found a combination of settings that reduces the garble.

Another possible solution is to enable the attenuation setting to dampen the reception on the scanner.

Hopefully this is a problem that Uniden (and other scanner manufacturers) can deal with eventually. There's been several posts on this topic in other forums.

I'm a fire chief and thus have a radio on the new system. There's a world of difference in the sound between a scanner and the radio, (but there's also a world of difference between the cost of the two).

I was on the phone with uniden rep yesterday and he said that was the first he'd ever heard of the issue and was going to bump it up the ladder and see what they could do if anything. I found it hard to beleive it was the the first time hearing about it. It's a shame. I feel like it's almost false advertising on both uniden and GRE part but have heard GRE scanners are a bit better in decoding. Manufacturers just aren't staying ahead of the curve.

 

[thewenk]

I was on the phone with uniden rep yesterday and he said that was the first he'd ever heard of the issue and was going to bump it up the ladder and see what they could do if anything. I found it hard to beleive it was the the first time hearing about it. It's a shame. I feel like it's almost false advertising on both uniden and GRE part but have heard GRE scanners are a bit better in decoding. Manufacturers just aren't staying ahead of the curve.

I'm sure Uniden knows about the problem. CS phone people generally don't know much about what is being worked on in product development, or if they do, they can't say anything. Uniden is very tight lipped about future products(keep the competition guessing), especially about technical issues. Don't sell Uniden short, they're staying competitive, as I'm sure GRE is. We'll hear about it eventually.

Dave

 

[Ben96cal]

re;

I'm sure Uniden knows about the problem. CS phone people generally don't know much about what is being worked on in product development, or if they do, they can't say anything. Uniden is very tight lipped about future products(keep the competition guessing), especially about technical issues. Don't sell Uniden short, they're staying competitive, as I'm sure GRE is. We'll hear about it eventually.

Dave

It has nothing to do about future products.. They are already advertising the fact their scanner can decode CQPSK modulation in P25 systems. If they can't they need to either stop advertising it's a feature or fix the issue asap.. They've had 2-3 years and still it's not fixed.

 

[mancow]

GRE has troubles too. I can't monitor a 700 system only 20 miles away with the Unidens or the GREs. At some point even Motorolas have an issue. It's just physics and there's not really that much anyone can do about it when the multipath is bad enough.

 

[northzone]

I am a little confused. You talk about Uniden having trouble with simulcast then you post a youtube link to a GRE scanner?

 

[Ben96cal]

re

I am a little confused. You talk about Uniden having trouble with simulcast then you post a youtube link to a GRE scanner?

I didn't have a uniden example so I used that. It's the same thing on a Uniden.

 

[Boatanchor]

There's a good 'Signalharbour' article on this issue that was first highlighted back in 2003!
Still, we wait for a 'fix' despite several new models of scanner and the increasing popularity of p25 simulcasting in the last ten years.

The Digital Diversity of APCO-25

Credit to the authors.

 

[k9jus]

to: OFD8001

i live across the river in clarksville just off of eastern blvd. what settings did you experiment with on your 996xt? Do i get to them from the menu? I really want to monitor louisville fire but having trouble.

 

[phantomdaz]

to: OFD8001

i live across the river in clarksville just off of eastern blvd. what settings did you experiment with on your 996xt? Do i get to them from the menu? I really want to monitor louisville fire but having trouble.

Yes, inquiring minds want to know
I live in Lexington but travel to Louisville. I am setting up the scanner tonight for Lou.

Any tips or tricks would be greatly appreciated

 

[ofd8001]

Sorry for the late response been out of town for a week.

You get to the P25 settings screen by pressing the HOLD button while powering up the unit. The screen will go through a series of colors. Then press the MENU button and scroll down to settings.

You will see P25 ADJUST MODE. Press the E and a numeric value appears. I set mine at 15.

Then hit the menu to back up to SETTINGS. Scroll down one line to P25 ADJUST LEVEL. Press the E and a numeric value appears. I set mine at 50.

This works for me, but I wouldn't be surprised if other combinations may work too. This is an exercise in "fine tuning" with trial and error being what it takes for the best combination.

 

[pliquett]

I don't know if this will help but I was having issues scanning the P25 system here in Indy and I changed the threshhold to manual instead of auto and set it to 7. Also From Auto to FM and it has made a world of difference. Try and see if this helps. Also unless they rotate their control channels lockout all but the main one closest to you. Good luck.

 

[RoninJoliet]

U can't change the "XT" models from auto to manual....?

 

[jsncrso]

Try a yagi!

Ben, I feel you pain. I scan one of the worst P25 systems there is (Dare County, NC, where most of the county is water). In fact its bad enough here that we are getting an additional Multicast system to mirror our simulcast system because many of the county radios are having horrible multipath interference issues as well (I know of a user who had to remove the antenna of his base radio and point it in the direction of the nearest tower). With that said, it's not completely Uniden's fault when $4,000 radios are having the same fits.


The *****BEST***** thing you can do is get a yagi antenna and install that (just make sure you aim it right, there is an excellent article on it on here and it picks up off-axis 800/VHF on other systems fine as well). Using the stock antenna, I was picking up around 25% of transmissions. With the yagi it's been 100% the entire time. It sucks having to sink more money into a $500 scanner setup but its very very worth it if you want to be able to scan a P25 system. Try this before you get to frustrated...the $70 I spent at ScannerMaster on LMR400 and the 10dB Terrawave antenna made a world of difference. Its weird listening to my scanner come in crystal clear when the sheriff down the treat is asking central to repeat traffic. Though there could be improvements to P25 scanning, The BCD996XT is an awesome scanner, but P25 is just a beast and Uniden can't change the laws of physics.

 

[jsncrso]

Also, if you are going to stick with the stock antenna, do like the others have said and adjust the threshold values. Read this RR Wiki article to understand the concepts of these values and how they are adjusted in your scanner for best performance:

P25 audio decode level adjustment - The RadioReference Wiki

It takes some playing around with, but short of a yagi, this works pretty well too.