BCD996T Digital Trunked recieving problem

[modernmidnight]

I have my scanner programmed to listen to a Motorola Type II SmartZone system in my county. I have it set up to use a site that is 2 miles away from my house. I have an antenna on my roof.

The problem i am getting is that the audio gets bad at some points. Sometimes it turns to static and sometimes it cuts out. It also sometimes makes a noise that an analog scanner makes if you try to tune it to a digital channel. Are there any settings i need to adjust to make it work correctly? I have tried bringing a portable radio home from my fire department and I had no issues receiving audio.

Any help is greatly appreciated

 

[ka3jjz]

Don't try to compare a commercial radio to a scanner - it's like comparing apples to oranges.

Let's start with some basic questions;

a. What system are you trying to hear? Go to the Database link under the site title and find the URL.
b. What is the antenna and what kind of coax? The higher the frequency the more loss there is with cheap RG58 type coax.
c. Did you try adjusting the threshold, mode or any other settings?
d. What firmware are you using?

I suspect a desense or simulcast distortion issue, but it's not possible to diagnose it accurately at the moment. Are there other sites for this system that are close to you geographically? Any cell sites on the same site as the public safety antennas (not uncommon)?

73 Mike

 

[modernmidnight]

a. Morris County Trunking System, Morris County, New Jersey - Scanner Frequencies I am using site 2 currently.
b. The antenna I am using is the first one listed on this webpage: http://tinyurl.com/y8pklxs All I know is the coax cable I got was shielded. I did not buy any fancy kinds.
c. I do not really know how to properly adjust the threshold. I have not messed with any other settings.
d. Firmware version is 3.01.00


That is the closest site to me. I can pick up another site but it does not receive as well. As for the site I believe there is a Verizon tower at that location. I could be wrong.


Thanks for the response Mike.

 

[ka3jjz]

Make sure that you have programmed this as a Moto Type 2, and not a P25 system. You can use the audio type setting on each talkgroup to indicate which talkgroups are digital, and which are analog. Are you using any software to program?

I also have a mix mode system in my county here in Maryland; if you are using FreeScan, you want the system to be 'Mot Type II / P25' and the site type to be 'Mot 800 Standard Type II'

If Verizon is indeed on the same site, then desensing is a strong possibility. Attenuation might help somewhat. However, you might be better served by using a yagi and pointing at one of the other sites. Pointing away from the Verizon site might introduce enough attenuation from the back end of the antenna to lessen the effect. It is also a possibility that you are running into some simulcast distortion issues, since there are 4 sites to that system, and you are running a discone (see this article in our wiki which describes the phenomenon in some detail...)

Simulcast digital distortion - The RadioReference Wiki

Here is an article about the decode threshold levels. It may help some (perhaps not much - it's quite possible you are getting clobbered by 2 different issues at the same time), but it may be worthwhile information nevertheless

P25 audio decode level adjustment (BCD396T) - The RadioReference Wiki

(it applies just as much to the 996)

Finally, the coax can be a real problem. RG6 or 9913 are usually the types recommended for their lower loss characteristics, particularly as you get higher in frequency. If you don't know the type of coax you have, find out. You could be losing a significant amount of signal if the run is too long. This table lists several types of the cheaper cable, and the loss that results...

Coax Cable Loss

73 Mike

 

[scanchs]

It might also help for you to upgrade to the most current firmware version (3.02.00). That version worked without any manual adjustments for a lot of folks. Of course, your mileage may vary...

ScanCHS

 

[davidmc36]

It might also help for you to upgrade to the most current firmware version (3.02.00). That version worked without any manual adjustments for a lot of folks. Of course, your mileage may vary...

ScanCHS

Second the firmware update. Didn't notice till just the other day that my 996 was a version or two behind. Cleaned up the digital quite nicely and improved the AGC a lot too.

 

[W1CMC]

Front end overload? Did you try an attenuator?

 

[modernmidnight]

Front end overload? Did you try an attenuator?

I tried. It did not help

 

[ofd8001]

I think I'm in the same boat as you are. The problem, and I'm sure if you read the the wiki articles, is that your scanner is receiving too good, as compared to too bad.

What you scanner is doing apparatently, is receiving more than one transmitter. If the transmitters you hear are not in perfect sync (timing) with each other, your scanner is going nuts trying to listen to both of them, and that comes in the form of garbled audio.

Your fire department portable has a lot more "circuitry" in it to resolve those multi-site conflicts, than does your scanner. So you, and I, are doomed to the too much receive paradox until the scanner manufacturers figure out a way to resolve this, without costing us an arm and a leg.

We were out on a car fire the other night. I was in my fire mobile listening to the scanner, and the audio was horrible on the police channels. Yet when I walked over to the cops who were there as well, the audio on their portables was pristine. There is a new P25 system that all public safety folks are migrating to, one having 12 simulcast sites.

 

[acepilot340]

ofd8001,
We are all in the same boat, digital is new and still not perfected in scanners. I have had better luck with 800mhz and 400mhz digital systems but for some reason those darn 700mhz sites always come in horrible with tons of gargle.

For the Illinois State Police system I can have 5 bars with the 700mhz site and it will still cut out and be unreadable; so then my scanner automatically switches to the 800mhz site located on the other side of the county that has 1 bar but comes in crystal clear.

Personally, I feel it is a problem with the 700mhz modulation, but I'm not an engineer so I can't be for sure.

But it's not the end of the world. Some would argue that even commercial radio systems are not perfected. The only digital system that is close to perfect is cellphone communication. So that's why I am going to wait a few years till I purchase a new digital scanner.

 

[davidmc36]

.....digital is new and still not perfected in scanners...... So that's why I am going to wait a few years till I purchase a new digital scanner.

With a 996T, PSR600, and a 396XT I have digital well covered for my area right now. With what appears to be quite a wave of services re-tooling, I would also want to give it a few years now to see what kind of systems are on the airwaves before blowing the dust out of the pocketbook again.

 

[billy245]

Does this problem happen when you are just using the rubber duckie antenna that came with the radio? If not, just use the duckie. You should be able to receive the tower only 2 miles away....