Greetings,
Our main dispatch channel has recently fallen victim to some very annoying interfearance.
The station is on R458.xxx, T453.xxx with a DPL of 243. The interfearance signal is apparently comming in on the recieve channel, keying our repeater (so it apparently even includes our DPL) and is repeated just like any conventional voice signal to all of the other radios in the county. We are located in SouthEast Kansas, about 100mi. from any major metropolitan cities.
The interfearance is in the form of short data packets (I haven't attempted to find a way to decode them) which sound like MDC1200 and last about .25 - .5 sec in duration. The packets seem to be spaced about 1-3sec. apart and a run of the interfearance packets may last anywhere from 20sec to 45min or more. They also seem to be occouring more often in the mid to late morning, however we have heard a few isolated incedents as late as 1700 or 1800hrs.
I had initially suspected a data transmitter located at the same site (local water tower) which is used to trigger the pumps for filling the tower, However I have monitored both frequencies (which are very close togather) at the same time and the interfearance is clearly comming from another source. I have to say that I'm perplexed. There are no other data radios operating in our county, unless there is a transient system that has been set up by a construction crew or something like that.
I would sincerely appriciate any suggestions or ideas which any of you might have.
Thanks in advance.
John
Mystery Data Interfearance. Please Help.
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As a total shot in the dark, you might want to try and search for Monty's previous thread on "UHF Freqs Being Jammed By Trimble Survay Eq".
Sounds like a possibility. Also, have you tried decoding the data as MDC? Is it possible that a user is accidentally or maliciously sending MDC emergency? It's unlikely that it would go on for 45 minutes, but......
Sounds like a possibility. Also, have you tried decoding the data as MDC? Is it possible that a user is accidentally or maliciously sending MDC emergency? It's unlikely that it would go on for 45 minutes, but......
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Thanks for the response. I'll check into the post on the Trimble system. I haven't tried to decode the data as MDC but will give that a shot later this week. I don't believe that it could be anyone "legitament" triggering their MDC emergency because I programmed all of the radios in the county and disabled MDC on all of the ones that supported it. There is of course the possibility that someone is "hacking" the system in that manner though. Could be worth a shot.
Hi,
I once had a problem with interference here in NY on a fire dept. low band freq. There was an intermitten burst which was causing transmissions to be lost because the signal was stronger than the portables in the field. I searched the building and all the trucks even disconnecting power to each truck radio one at a time. I was convinced it had to be there own equipment. But I could not track it down. I also checked with the buildings around them to see if they installed any new equipment. Still could not find it. So I decided to called the FCC (just for the hell of it to see if there was anything they could do, but expecting them to tell me I'm on my own..... Boy was I wrong....) they told me someone would get back to me (I figured some time next year) in about an hour I was contacted by someone who said they would meet me in the morning at the site. This guy showed up with this unmarked car with all sorts of tracking equipment and radios mounted between the seats. From the outside you could not tell a thing and not one single antenna was to be seen. He showed up as promised and had me get in the car and we drove around town and tracked the signal for several hours (remember it was intermitten) When we narrowed down the signal he than used hand held equipment and we atttemped to narrow it down even more. At one point we had it narrowed down to the signal being very strong neat the electrical service and there was some thought given to some sort of equipment that the utility (at the time Lilco which is is on Iong Lsland) so he made a call to someone there and in ten minutes thay had someone at the site (I guess when the FCC say be here they say yes and how high)This guy to came in with some hand held tracking equipment and again we searched the building. After about another hour It was decided that it was not the utiliity's problem and that the signal was somehow being injected into the electrical line. We did eventually find the source ...... the point being that during the day in speaking with the guy from the FCC I had told him I was quite surprised that they reacted to our complaint so fast and he replied that if it involves life saftey they come out right away ... You didn't say what you freqs are used for but you may want to try contacting them and see if they will help you.
By the way getting back to this car...... I asked abouth how all the equipment in the car worked without any shown antennas and was told he could not tell me how they do it.... It is some special designed equipment for them..... But like I said if you saw this car comming down the street you would never know what he was doing.
OH by the way the signal.........
It was comming from a MT-500 that was in a converta com mounted in a side compartment burried behind other equipment on a fire truck that no one seemed to remember about. The radio was hardley ever used and the converta come must had gotten wet several times because you could see the corrossion. As far as the signal getting into the electrical system there was a remote antenna connected to the converta com and when the truck was parked the antenna was touching against the conduit. What had thrown us off early in the tracking was that when the garage door was down and you were in front of the building you did not get a very strong signal from the front of the building.
Sorry for the long post.
Gary
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:04 ]</font>
<font size=-1>[ This Message was edited by: gmc on 2002-03-25 10:09 ]</font>
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:10 ]</font>
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:12 ]</font>
I once had a problem with interference here in NY on a fire dept. low band freq. There was an intermitten burst which was causing transmissions to be lost because the signal was stronger than the portables in the field. I searched the building and all the trucks even disconnecting power to each truck radio one at a time. I was convinced it had to be there own equipment. But I could not track it down. I also checked with the buildings around them to see if they installed any new equipment. Still could not find it. So I decided to called the FCC (just for the hell of it to see if there was anything they could do, but expecting them to tell me I'm on my own..... Boy was I wrong....) they told me someone would get back to me (I figured some time next year) in about an hour I was contacted by someone who said they would meet me in the morning at the site. This guy showed up with this unmarked car with all sorts of tracking equipment and radios mounted between the seats. From the outside you could not tell a thing and not one single antenna was to be seen. He showed up as promised and had me get in the car and we drove around town and tracked the signal for several hours (remember it was intermitten) When we narrowed down the signal he than used hand held equipment and we atttemped to narrow it down even more. At one point we had it narrowed down to the signal being very strong neat the electrical service and there was some thought given to some sort of equipment that the utility (at the time Lilco which is is on Iong Lsland) so he made a call to someone there and in ten minutes thay had someone at the site (I guess when the FCC say be here they say yes and how high)This guy to came in with some hand held tracking equipment and again we searched the building. After about another hour It was decided that it was not the utiliity's problem and that the signal was somehow being injected into the electrical line. We did eventually find the source ...... the point being that during the day in speaking with the guy from the FCC I had told him I was quite surprised that they reacted to our complaint so fast and he replied that if it involves life saftey they come out right away ... You didn't say what you freqs are used for but you may want to try contacting them and see if they will help you.
By the way getting back to this car...... I asked abouth how all the equipment in the car worked without any shown antennas and was told he could not tell me how they do it.... It is some special designed equipment for them..... But like I said if you saw this car comming down the street you would never know what he was doing.
OH by the way the signal.........
It was comming from a MT-500 that was in a converta com mounted in a side compartment burried behind other equipment on a fire truck that no one seemed to remember about. The radio was hardley ever used and the converta come must had gotten wet several times because you could see the corrossion. As far as the signal getting into the electrical system there was a remote antenna connected to the converta com and when the truck was parked the antenna was touching against the conduit. What had thrown us off early in the tracking was that when the garage door was down and you were in front of the building you did not get a very strong signal from the front of the building.
Sorry for the long post.
Gary
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:04 ]</font>
<font size=-1>[ This Message was edited by: gmc on 2002-03-25 10:09 ]</font>
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:10 ]</font>
<font size=-1>[ This Message was edited by: GMC on 2002-03-25 10:12 ]</font>
We get the same thing around Pittsburgh. It seems that some of the pager companies are interfering with both public safety and ham. It's intermittent and does sound similar to MDC1200. The main offending transmitter is miles away, but on the hilltops, you'll get it- especially on a repeater.
You need to track this interference before doing anything else. If you're not familiar with doing this, check with some local ham radios clubs. Many of these people live for "fox hunts" (finding hidden transmitters) and would be glad to help.
You need to track this interference before doing anything else. If you're not familiar with doing this, check with some local ham radios clubs. Many of these people live for "fox hunts" (finding hidden transmitters) and would be glad to help.
It might be some kind of remote control system for a sprinkler system, or something similar. I think it might be called MOSCAD or something, and I think its sold by Motorola.
The city I live in uses such a system, which consists of a VHF-Hi repeater using DPL 243 (possibly a system default), with the sprinkler controllers in parks throughout the city randomly transmitting into the repeater. The sprinkler controllers have the VHF "transit style" fin antennas on them. The data does sound similar to MDC-1200.
Just a thought...
The city I live in uses such a system, which consists of a VHF-Hi repeater using DPL 243 (possibly a system default), with the sprinkler controllers in parks throughout the city randomly transmitting into the repeater. The sprinkler controllers have the VHF "transit style" fin antennas on them. The data does sound similar to MDC-1200.
Just a thought...