talkgroup crosstalk on smartnet system.

[N9LLO]

Help. I just started getting lots of crosstalk on my 900 system. During the repeater hangtime you can hear other talkgroups coming through on the gold elite consoles, sometimes on the handhelds. That lends me to think it may be a spuriouis tx on the system? Maby a mix somewhere, it is a very closed spaced system. I need to start checking things tommorow to see whats going on, any help would be appreciated. could this be a CEB problem?

Help
Chris
N9LLO

[KE9GK]

Chris,

We have the same problems...and have had them for quite some time on our 800 smartnet II system where I dispatch. The centracom gold consoles are the only things affected by the cross talk...none of my field units hear the "cross talk"...but it is there plain as day in my headset...most of the time it is noisy...but there are some times that it is so clear that i think squads are on the wrong channel....and sound like an idiot for yelling at something no one else in the field heard. I have told our radio services guys about it...but alas they have found nothing. In fact we get the cross talk over one of our VHF channels as well (as in we hear certain trunking system talkgroups over the VHF resource - weird) Hope someone has some insight as to why...so that I can bring it to them as well!

Don

[wavetar]

Chris, I have seen your issue a couple of times over the years & it turned out to be the filtering equipment. Monitor the actual repeater freqs & determine which one is susceptible to broadcasting the unwanted audio during the hangtime. Hopefully it's only a single repeater freq causing the problem. From there it's pretty simple to figure out which repeater freq is getting leaked through, and take the steps to tune/fix/replace the offending piece of filtering equipment.

Don, I have seen your issue or similar as well. Do you only hear it in the headset? Are your consoles local or remoted? My bet is there's a BIM or TBIM with the data/mux bus jumpers in the incorrect place.

Todd

[KE9GK]

Wavetar,

Yeah...in the headset and on the unselect speaker as well...depending on which talkgroup decides to act up. It is not always there...just sometimes...but lately its been getting worse. It seems to be the crappiest when the weather is humid/damp...your typical bad RF days. Our setup is pretty typical....we have 15 OP's on the floor and 1 OP in the equipment room where the CEB is located. We have a dedicated fiber optic link to the central controller / VHF base stations....with copper redundant backups. We do have 2 MCS/GM300 mobiles tone remoted locally as well, but to my knowledge those resources have never had the interference issue. The radio services guys never seem to believe us..cuz they cannot hear the cross talk on their portables when they are monitoring....so obviously its not happening and all of us "minions" are just hearing things !!!!

Thanks for the input
- Don

[wavetar]

The description of your problem leads me to think the trouble (whatever it may be) is with a specific repeater channel which is chosen as one of the last in line in your trunked system. Some days when your system isn't busy, the repeater isn't chosen much, or at all, and the problem doesn't show. Other days when the system is busier the repeater gets chosen much more & the problem becomes aggravating. Something to try if your system isn't busy to capacity is disabling a single repeater at a time at the trunked site. Disable for a day or two, try a different repeater each time...see if the problem goes away. If this works & you determine which repeater it is, then you can start looking for crossed lines, incorrect TBIM jumper settings, etc. The fact the field units don't hear it leads me to believe it's not with the filtering equipment.

I'd start with the repeater chosen last in line & work my way up from there. It's usually, but not always, the highest numbered repeater. Often repeaters which are used for secure comms or phone line interfaces are set in the controller to be chosen last, so they can remain available as long as possible for their intended purposes.

[N9LLO]

I think I have found the problem although it dosent quite make sense to me yet.
I could not verify any crosstalk problems on the handhelds only at the console.
Only coming through on the selected talkgroup in the operator headset not on unselect audio.

The system was running on generator power during our annual substation maintenance here at the plant. After 11 hours the generator quit and the system ran on battery power for the next hour or so. This is a 10 channel 900 system 28 channel cardcage with a t5562a startsite 3 channel telephone interconnect up at the system. 24 copper pairs carry 4 wire audio and dual Timi link data back to maintenance dispatch, about 3/4 mile of copper to the CEB and 4 gold elite terminals.

The startsite phone interconnect was not ups backed up and lost its programming.
Phone is supposed to be on channel 5-6-7. when you would try to use it it would come up on any avaliable channel and none of them really worked. I decided to try and track this problem down first, seemed a little easier than the crosstalk issue. Using the Tell command set in the System Manager I checked the interconnect setup. ALL repeaters were enabled for interconnect and ALL the interfaces were enabled. I disabled the interconnect for all repeaters except 5-6-7 and all interfaces except 1-2-3. This got the phone working again.

The crosstalk problem also went away. The crosstalk was not related to attempted phone usage but normal talkgroup calls. Dont ask me why (maybe someone can tell me why) this was happening. I think the crosstalk was only coming from repeaters normally associated with the interconnect (5-6-7) but i'm not 100% sure of that

Chris
N9LLO