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Solution to monitor for interference

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seapdx
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Solution to monitor for interference

Postby seapdx » Thu Nov 17, 2016 10:27 pm

I'm looking to program a receiver with all my base transmit and receive frequencies to place up at each of my ten radio sites. The receivers will be connected to the receiver pannel that also feeds my MTR2000 stations (public safety). I'm thinking about using some APX mobiles I have sitting around to serve as the receiver (or CDM's - I have both). The point is to listen for interference on the frequencies and be proactive in trying to resolve any interference. My problem is this: I want to be able to remotely monitor each of the radios at the ten sites. Ideally I'd put the 24 frequencies in the radio I want to monitor, hit scan and all is good. But, if I am monitoring remotely and pipe the audio into a path back to the office, how do I know what frequency I am hearing the interfere on? Short of putting a CCTV camera on the display of the radio, i'm not sure that I can do what I am looking to do without a radio dedicated to monitoring each frequency.

Suggestions? Ideas? Thanks

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wavetar
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Re: Solution to monitor for interference

Postby wavetar » Fri Nov 18, 2016 3:34 am

The only thing that comes to mind off-hand is a digital remote setup, like an APX7500 consolette and MCD5000 remote. You would need an IP link from the site to your office. The remote acts as an extended control head to the consolette, so you would see the corresponding channel name when something comes across the scan. I'm pretty sure the APX can scan 32 channels, but not positive. Motorola's historically only do 15/16, such as your CDMs.
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Bill_G
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Re: Solution to monitor for interference

Postby Bill_G » Fri Nov 18, 2016 4:47 am

With twenty four freqs at ten sites, I'd look into a logging scanner. Would require an ethernet link to each site to control the devices, and recover data.

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xmo
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Re: Solution to monitor for interference

Postby xmo » Fri Nov 18, 2016 11:44 am

With the proliferation of spectrum use, being proactive and monitoring for interference to your system is becoming more important than ever for system administrators.

With older radio systems your users could recognize interference and report it but with modern systems all they notice is that things don’t work at times. Motorola trunked systems do take channels out of service if an “illegal carrier” threshold is exceeded but that can take as long as 50 seconds – depending on the default settings. Even setting the interference timer as low as ten seconds can miss a lot of situations if the interference is coming from a system where transmissions are short – like public safety systems often are – three to five seconds being typical.

For these reasons, having equipment at the system’s sites to report interference events can be an important tool for the system administrator. One possible monitoring solution would be to put a receiver or receivers at each site to monitor all the system’s input frequencies. These receivers would be connected to the site receiver distribution so they would be affected exactly the same as the system’s receivers.

One problem with this idea for 800 MHz systems is that simple (cheap) mobile radios don’t receive the input frequency range. A second problem is how to differentiate the unwanted interference from legitimate signals. Also, a single scanning radio could miss short events. On an active system with many channels a scanning radio would be a less than ideal tool.

These problems can be surmounted by the use of the system’s own receivers to identify interference. With a trunked system using Quantars this is easy. A trunked station should only receive a signal when it is assigned – in which case it is transmitting. A wildcard program can monitor for RX activity when NOT keyed and then assert an output [I/O pin] – thus reporting any signal that shouldn’t be there. (Obviously this won’t identify an interference event that comes in on top of an active user.)

Interference wildcard outputs from the base stations can then be connected to the system’s fault management system (e.g MOSCAD) and reported back at a central point. Logging the interference audio at a central point could be done in several ways depending on what connectivity is available from the sites. If there’s limited connectivity but one voice path is available, logging could be accomplished with a multi-channel radio at the site steered to the frequency that’s being interfered with by the wildcard I/O.

You would then pass that audio back to a recorder at the central location and you would use the fault management time stamped interference log to identify which channel was being recorded.

seapdx
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Re: Solution to monitor for interference

Postby seapdx » Fri Nov 18, 2016 11:55 am

Thank you all for the feedback. All good information. This is a VHF conventional system, still analog (MTR2000's). The transport/backhaul is T1 based microwave. I won't have IP links until we transition to a new, more current microwave solution. In regards to the logging scanner, Bill_G: can you message me with any links to these devices? I'm not familiar. I am concerned with using cheaper equipment to monitor given the receiver specifications are not typically that great on cheaper equipment. Thanks

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Bill_G
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Re: Solution to monitor for interference

Postby Bill_G » Sat Nov 19, 2016 5:20 am

The Icom R9500 is anything but cheap. It's a pretty good piece of test equipment. You probably only need one, and you can move it from site to site. This can be controlled via RS232. So, it will fit within your T1 limitation with some constraints on what you can do. But, it will record every receive event you have it monitoring. You can come back later to review it.

seapdx
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Re: Solution to monitor for interference

Postby seapdx » Sat Nov 19, 2016 1:43 pm

I'll take a look at that. Thanks.


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