Batboard

Centracom II console, here is the problem...

On our main band, which is a remote base station (at another site) controlled by a UHF link, we get a 2-5 second audio distortion after a quick-call II is put out. The tones are perfectly clear, followed by extremely "fuzzy" voice. This causes the first part of the transmission to be not understood. After that period, the message is clear. This does not occur if they just key to transmit, only after a set of tones have been triggered. It only occurs on this freq, and none of the others controlled by dispatch including our back-up base at that location. Another dept uses the same link, and they are not experiencing any of these problems, so that rules out the remote base. I checked our UHF link radio, and it seems to be working fine. I think it is occurring somewhere between the dispatch mic and the link radio. I had a repair company come out and everything worked perfect during their visit. This has occurred the last couple of weekends, then ceased for the week.
Is it possible a cell phone placed near the control point could cause this? But only on our freq for a couple seconds? They run several other UHF and VHF frequencies without problem.
Any other ideas?
Thanks.

Ah I see the problem,

You need a Orbacom....ha ha ha just kidding

I am not a Centracom expert, but it'd be worth it to hang a test tone remote out of the CEB and see if you hear the fuzzy audio there. That would at least clearly define where it's being generated...from the console or the wireline/rf link.

I am willing to bet you will hear it come out of the CEB. Again, I am not the Centracom expert (was denied the class) but might have to start swapping CEB cards .

Also, does it happen if you alert on another BIM card ? If it's just one BIM, then you may be in luck, if it's on all the BIM's then you got a bigger problem.

Just my .02 cents. Hope it helps. I am sure the experts will be stepping in here any moment

Matt N3IVK

it sounds like it could be something in the Centracom, but it would help me if I knew a little bit more about your system:

1. Do you have more than one dispatch position? if so, did you hear the few seconds of distorted voice on those?

2. If this for public safety, you should have a logging recorder attached to that channel. where do you have it tapped for logging, and if possible can you attach a audio sample of the problem?

3. N3IVK was right about the BIM cards. it might be a good idea to swap one bim with a spare to see if the problem continues. (remember to set your address dipswitches correctly.)

4. does it happen at any perticular time of day? or more straight to the point, does it happen when that one certain dispatcher is working

let me know what you find. I would like to help.

-WEC

ACME product tester

2 dispatch positions. Has occurred on both, but more on 1 particular side.

We have voice print, but I do not have access right this moment.

Seems to occur on Weekends, but has occurred on weekdays from time to time. It just started 3 weeks ago. It is noticeable with about 3 dispatchers. It seems as though all of them are placing cell phones ( Cingular/Nextel) within 12" of the mic and console screen. The dispatchers that don't do this don't seem to trigger the problem.

Most of the time occurs on 1 frequency, but the Nextel has been known to cause interference on other freqs in the console.

Hypothesis: Don't put your cell phone near the mic or console. I am going to try this first. I have spent 5 hours worth of callout service already (nothing found), and the charges add up quick.
What do you think??

Hrm, You mentioned "screen" I take it's a CRT based console then. Either the DOS based Centracom or the Gold Elete thinggy.

Alot of CRT monitors dont seem to care for the Cell phone/Nexthell devices. I'd say bring your cell along next time and try to replicate the problem, if it comes back then yea...ya gotta post a sticky note saying "Thou shall place no cell phone near the console...thanks, God" or something like that.

Been wanting to goto Centracom school, but I guess it's too late now since the MCC500 is coming out.

So both positions do it, the comman denominator here is :

1. They both use the same CEB.
2. Same dispatcher is carrying the phone from position to position.

What would be interesting to find out is if you get the noise if you belch out a QC alert on a different channel. IF they dont normally do it, maybe you can do it for "testing" purposes. If that same noise is heard on another channel hooked up to the console, then yea.....it's in the console.

The idea with the cell phone is a good one, I think you might be on to something here. Back when I had a Nexthell it totally tore up my 19 inch CRT at home. Also got into the PC speakers, and just about everything around it. Couldnt see why it couldnt get into the console. If it's a CRT based Centracom, then the Mic/Speakers..etc is in a beige plastic box that sits under the CRT. If i remember, they were not shielded.

To make it easy for ya , tell em to leave the cell phone in the locker room If the Nexthell is used for operations, maybe a Iden mobile with a antenna stuck elsewhere would help ??

I like the idea of the sticky note on the console, it will match the others well We all know Centracoms seem to grow 3M post-it notes heh heh

Here are some suggestions :

1. "No cell phones at the console"
2. "Leave the cell in your car"
3. "Roaming charges ....21 cents, your monthy cell phone bill ....$39, bringing your phone too close to the console and paging out the radio shop at 3 AM...PRICELESS"


Sorry for the humor, but it's how I get through the day.

Matt N3IVK

The weird thing is that it only happens on the one channel. None of the others.

The other agency sharing the rf link has no problems.


In the last 18 hours, no cell phones near, no strange noise.....

Just as an FYI -

If you do use Nextel phones for work as some kind of backup dispatch, /\/\otorola does make a Nextel interface signaling BIM. this will allow you to still use Nextel for dispatching yet keep the actual phone away from your sensitive CIE.

Speaking of the CIE - if it is getting interference from cell phones, you might want to make sure the little grey grounding strap to the metal cover is attached on the back. Some installers & tech's get lazy and skip that step. This can cause big problems with outside interference.

Let us all know how things shake out!

-WEC

ACME Product tester

After further "testing" I am now 97% sure the cell phones are causing this. Particularly.....NEXTEL.

I had one dispatcher (Nextel) call the other dispatcher (Cingular) and transmit at the same time. BINGO! Duplicated interference.

I told them to relocate their cell phones away from the equipment. Everything seems to be normal. I hope this is it.

Thanks to everyone who helped out. I will let you know if anything else pops up as a result.
Thanks!
Ett1033

I had a simular problem with my fire QCII tones, I corrected this by disableing the ALC (Automatic Level Control) on the MSF-5000 repeater.

Larry

AH HA! I heard it occur on another frequency. This rules out the RF link. I do believe it is definitely cell phones!