Pro 106 and simulcast distortion?

[rkwalker86]

Recently, my pro 106 reception of our local police dept transmissions (P25, simulcast) has been terrible. From not receiving anything to cutting in and out so much you can't understand anything. The trunking "T" on the display is on and off and very unstable. I've confirmed in another thread that others are receiving these transmissions with no problems. And, while driving around town, the scanner works fine. So the problem is while I'm at home. I've tried everything I can think of without any luck. I ran across a description of simulcast distortion and it sounds a lot like what I'm experiencing. So here's my question: Is it possible that the signals that are supposed to be transmitted at the exact same time have recently gone out of whack? Does that ever happen? I've had this scanner for almost 2 years and never experienced any signal weakness, let alone what's going on now. Curious if anyone has had a similar experience, and what their outcome was. Thanks.

 

[rdale]

It's possible. Or maybe there's something else popping up around you transmitting. Or it's a combination of spring growth and weather.

Try a new antenna, a new location in the house, etc.

 

[rmiller818]

Location is the biggest factor. At my house the reception is hit or miss. Some days it is great, other days it almost is not worth listening. Most of the time it is somewhere in between.

You can try some different antennas, change some settings (try turning the attenuator on ONLY for the system, not the global attenuator. I leave it on all the time), or you could try using a yagi antenna.

 

[rkwalker86]

Thanks for the responses.

I have tried the attenuator off/on, played with settings, switched antennas, and moved to different positions in the house. The frustrating part, the part I don't understand, is the reception in the house (anywhere in the house) has always been great. For close to two years I could place the 106 in any nook or cranny inside the house and there were no problems. Oh well, maybe one day soon things will return to "normal".

 

[zerg901]

Are the users of the system complaining of radio problems?

Maybe a new cell site activated near your house. Maybe they recently upgraded to a 'synchronized simulcast' system. Maybe the nearest tower has a bad antenna. Did someone turn on a new computer near you? Maybe they cut their Xmit power. Is this a 800 Mhz system? Does it just happen on windy days? Foggy days? Are you having reception problems on any other channels? Maybe they upgraded to a new version of P25 that gives Pro106s problems. What signal strength are you getting? How does the signal strength change when you turn on the attenuator? Are far are the closest tower sites to you?

Peter Sz

 

[citylink_uk]

It sounds like you may be located in an overlap zone between sites.

Here is a quick example diagram to show what i'm talking about.



The Red + are the sites and the grey shapes show the prime coverage of that site (different shaped = different antenna patterns ect.)

Where the coverage overlaps between two sites (blue shading) the signal is carefully controlled to make sure the signal arrives at the radio at the correct time to avoid distortion. The green shading shows where more than two sites overlap. These areas are extremely likely to cause problems in a system. With analogue, you would just get more distortion, however with digital you would be lucky to get a stable decode.

This is why it's so important that simulcast systems are set up with precision and with the correct number of sites, antenna patterns and optimum antenna heights. Unfortunately many of agencies want to re-use only existing sites which may not be located in the optimum locations for simulcast, or to use too few sites with which leads to large unstable overlap areas.

I suggest the best thing to try is to make a cheap YAGI antenna. Check your location in relation to the transmission sites and try and position the antenna so that it gives a better reception off one site, whilst nulling out another with the back of the antenna.

It's probably just going to be a case of trying to point it in different directions and find what's best. Hope that helps in a some way.

 

[fourthhorseman]

citylink,,
thats a good explanation of a simulcast set up..
the graphic makes it easy to see..

 

[RoninJoliet]

Being in N-ILL you may be trying to hear the ILL Starcom system....On my 996XT using a ChannelMaster 5094A with 9913 coax i was getting over the winter 4-5 bars on the 700mgz towers in Chicago area...Now with spring and "buds on trees" im getting some days 1bar, other days 3bars and i did not change anything...I took my 396XT west here in ILL and followed just the 800 stand alone towers and they perform perfect even in a mobile...Multipath=YUK.....

 

[guitarbrian30]

newest shack upgrades

did you just update your scanner with the newest upgrades? Was this the cause?

 

[Twister_2]

I'm also having a severe problem with decoding my P25 simulcast system. I know its not just me lol.

But I must say if this problem just happened for you, it might just be the leaves growing on trees or possibly an update you preformed with your scanner (if at all).

 

[rkwalker86]

Thanks again for all of the responses, iformation, and ideas.

To answer some of the questions: As far as I know, no one else is complaining about the system. I did post in the Illinois forum asking. So far, 1 person has responded saying they are having no issues. There are no new electronics / computers in the house. The problem does not happen just on windy, foggy, or cloudy days it happens everyday, all the time. The problems with reception began before I upgraded the scanner software and continues after the upgrade. The attenutator has minimal effect on signal strength. As far as distance to the nearest tower, I am about 1 mile away.

I guess it could just be weather, trees, simulcast distortion, or interference from something else. But, again, it's frustrtating because in 2 years nothing like this has ever happened before.

 

[jackj]

Poor reception

Thanks again for all of the responses, iformation, and ideas.

To answer some of the questions: As far as I know, no one else is complaining about the system. I did post in the Illinois forum asking. So far, 1 person has responded saying they are having no issues. There are no new electronics / computers in the house. The problem does not happen just on windy, foggy, or cloudy days it happens everyday, all the time. The problems with reception began before I upgraded the scanner software and continues after the upgrade. The attenutator has minimal effect on signal strength. As far as distance to the nearest tower, I am about 1 mile away.

I guess it could just be weather, trees, simulcast distortion, or interference from something else. But, again, it's frustrtating because in 2 years nothing like this has ever happened before.

Is this system a trunked system with multiple towers? My suggestion is to borrow a radio from a friend (not the same make or model as yours) and try it in your house. If it does the same thing then you need to look for the problem outside of your home. I'm not familiar with your radio but if it can be setup to display the frequency of the traffic channel then you might take note of the problem frequency(ies) and take your radio to each of the towers in turn. See if the frequencies are the same at both towers. If they are, then you are dealing with a poorly designed system and there is little you can do to fix your problem.

As I have said before, a properly designed system will NOT reuse the same frequencies at adjacent towers. Even tightly controlled antenna radiation patterns will not completely eliminate coverage overlaps and those overlaps in a digital system will make it unusable inside the overlapped area. Timing of the digital signal, as others have suggested, wouldn't improve the problem. I won't get into all of the technical reasons why but it has to do with the fact that as your receiver's antenna moves around in the overlap area the distances to the towers changes non-linearly. So the transmission delay from each of the towers changes and the 1's and 0's are no longer in phase.

Edit: I just went back and re-read your original post. Forget about the question about trunked systems. Sorry.

 

[zerg901]

Are we sure this is a synchronized simulcast system? Any new skyscrapers or metal billboards in your neighborhood? Maybe there is a new transmitter in the neighborhood throwing sideband power onto the freq you are trying to receive? Maybe you are getting an image on the freq? (ie I hear my local DPW on 158.76 and 159.165 - they are licensed for just 158.76 - 159.165 is apparently a sideband of the 158.76 signal).

At this point, after rereading all the posts several times, I am guessing that NEXTEL turned on a site near you - or the PD upgraded to a synchronized simulcast system - or (less likely) the PD synchronized system needs to be retuned - or a combination of all of these.

Peter sz

 

[RoninJoliet]

I don't think you have actually said what system your talking about but again if its the Starcom system there is still work being done on it...I have a site about 3 miles away thats awful but the sites that are 20 miles away are much better...Thats the "multipath problem...My own personal opinion is my 396XT Uniden decodes the ILL Starcom digital system much better than the RS/GRE , especially in the mobile near cell sites the RS/GRE are awful but the Uniden 396XT is not bothered....

 

[rkwalker86]

Great thoughts, guys.

The system is the Starcom 21 Statewide Illinois P25, Winnebago County Simulcast.

Zerg901, the Nextel idea is a good thought. I will see what I can find out. I had to laugh when you said, "Any new skyscrapers...in your neighborhood". The closest thing to a skyscraper around here is a corn crib!

Thanks again to everyone for their help!

 

[SOFA_KING]

Loose antenna screw issue known to happen on these radios???

How do the weather channels come in? Any loss there?

 

[zerg901]

Since you are only 1 mile from the tower - have you tried taking the antenna off your scanner? Maybe you are getting "too much" signal. (IIRC you said the attenuator does NOT decrease the signal).

I think the NEXTEL signals affect the scanners by putting too much signal into the scanner, and driving some circuits out of whack. (Maybe someone else can explain what thats all about). Desense - out of band signals - intermod - etc

Peter sz

 

[jamesa53]

I don't think you have actually said what system your talking about but again if its the Starcom system there is still work being done on it...I have a site about 3 miles away thats awful but the sites that are 20 miles away are much better...Thats the "multipath problem...My own personal opinion is my 396XT Uniden decodes the ILL Starcom digital system much better than the RS/GRE , especially in the mobile near cell sites the RS/GRE are awful but the Uniden 396XT is not bothered....

Yes Ron you are right on that.....whenever I go to Naperville and monitor the Elgin tower with my 106 the simulcast distortion is pretty bad. Thing sits there and the display literally flashes when hooking on to one of those 700 Mhz control channels. Well DuPage County is now going Starcom and that will make it all better LOL.

 

[OsloViking1975]

This might help you maybe. Press PGM, Then FUNC, Then F3 this is from poster NDRADIONUT The zeromatic feature simply helps the scanner lock onto the correct frequency during search and sweeper modes. When zeromatic is turned off the scanner may stop on the frequency above or below the correct frequency.



5 Khz Other
In Lo 170 170
In Hi 480 480
Out Lo 150 150
Out Hi 530 530
You can try this one too if you want.
...In LO..........170..................170
...In HI...........610..................610
..Out LO........170..................170
..Out HI..........610..................610

 

[jamesa53]

This might help you maybe. Press PGM, Then FUNC, Then F3 this is from poster NDRADIONUT The zeromatic feature simply helps the scanner lock onto the correct frequency during search and sweeper modes.

Correct, this feature is only used during search mode and has no effect while the scanner is in scan mode. So I dont understand how this is going to help the problem.