900 Spread Spectrum Interference?

We’ve recently started having interference issues with some 900 MHz customers in a certain area. When the SM’s in this area register, signal levels are good.
Using an SM in spectrum analyzer mode, I see random spikes of very strong signals, as high as -38, on various frequencies. A service monitor in spectrum analyzer mode shows the same thing: strong momentary random spikes throughout the band. The activity seems to decrease at night. This looks like some sort of spread spectrum issue. Has anybody come across this before? If so, how’d you deal with it?

Jim Bremer


I have seen instances similar to this but with a couple of different causes,

1. Really cheap and nasty masthead amplifier (for FTA tv)

2. A regional water board who setup remote monitoring with 900 meg gear on the same frequency pumping out as much wattage as they could but doing it as and when they needed to report a change in water level

3 and irrigator using a remote monitoring sytem on his big travelling irrigation gear.

all were very hard to pinpoint and in 2 of the three cases we implemented frequency changes and sched changes to work around the issues.

It’s going to be hard to locate the source of interference using the SM analyzer. The SM can only give you a slice of time.

You might want to get a spectrum analyzer that you can put an external yagi antenna on for some directionality. Sweep it around until you get the strongest reading. Draw a line on a map indicating the direction. Move to another location 4 or 5 miles away and repeat. Move to another location 90 deg from the last and repeat. This will triangulate the position of the source and with some luck you will locate the transmitter(s).