Motorola XPR8300 background noise/interference

[BlueDevil]

I have a Motorola XPR8300 VHF Analog Repeater without an external power amplifier that all of a sudden has a lot of background interference or noise.

The repeater is on a mountain top however a long ways from any other transmitters. It is the only radio repeater at its location. It is used for a ski resort. The repeater has been operating well for the last several seasons. We have not had any issues with it until now and nothing significant has changed or is obviously broken.

Yesterday was the first day I was on location to obtain first hand observations and perform and troubleshooting. To me the repeater sounds like it could be feeding back into itself. Portable radios operating in close proximity to the repeater always sound good, loud and clear, strong signal and no background interference. However portable radios (multiple different makes and models) that are a further distance away produce a strong signal although there is a lot of background noise making their voice unreadable or at least very distorted. While dead keying a portable radio in an area that was known to experience interference when transmitting I noticed that the interference would increase in strength and pitch as if it was ramping up and then it would completely drop out. At that point the repeater was operating like it use to. It the signal was strong and sounded great from all locations on all radios. Upon immediately keying up the repeater again no interference was noted. If the repeater sat idle for a little bit and then was keyed up again the interference came back. When dead keying the repeater the interference was present and progressively increased in severity until it dropped out completely which took it about 10-15sec to complete.

For some additional information we are running a Telewave 4 Cavity Duplexer with a 4.5Mhz split and a StationMaster antenna. The interference seems to exist when operating off of both AC and DC power. The 3 second hang timer has a very clean and strong signal and the interference is never present during the repeater hang time.

Any troubleshooting ideas or suggestions on what maybe causing this interference/background noise?

 

[WA0CBW]

Have you done a desense test? checked the antenna SWR? It could be that something has happened to the antenna or coax or the transmitter has become spurious. It is also possible another signal has been put on the air that you are unaware of. You are going to need some test equipment (service monitor/spectrum analyzer/power-SWR meter/) to identify what is going on.
BB

 

[BlueDevil]

I did test the SWR of the Antenna and Coax Feed Line. I was getting readings within the acceptable ranging on both the TX and RX frequency. The readings were right around 1.25 I don' have a spectrum analyzer but I do have a service monitor that I am learning how to use. I don't have a power/watt meter but I haven't noticed any difference in the coverage area. Upon inspecting the coax feed line yesterday I did find a small section of the coax that has the black plastic sheathing rubbed off of it exposing the copper braid. This looked like it may have been there for a while and the interference we have been noticing started occurring rather recently. I am anticipating replacing the feed line and possibly the coax from the transmitter to the duplexer as it appears it is LMR-400.

 

[BlueDevil]

Well I made it back to the site today and took some additional equipment with me. It appears that the interference has very little to nothing to do with out repeater system. I was able to take some videos of some of the distortion and interference we have been experiencing. It appears that we are getting a weak signal interfering with our repeater input frequency (158.9400) A few times I thought I could hear a faint and unclear voice but never could make anything out. I will post links to the videos below. Any thoughts or suggestions?

https://youtu.be/7pAD7KzXbLY (This is what the interference/distortion sounds like coming through the repeater)
https://youtu.be/L4VS5fhpicw (This is my Yaesu VX-150 tuned to our repeater input frequency standing near our repeater site with a 3" rubber duck antenna)
https://youtu.be/_2oEKwyRPDw (This is my Yaesu VX-150 connected to our repeater antenna tuned to our repeater input frequency also showing that the signal is being broadcast with a CTCSS tone of 179.9Hz)

 

[kayn1n32008]

I see you are in Washington state... Your input frequency is a common trucking channel in BC called LAD 2. Many folks do not care that it has area restrictions, or that you must be licensed in BC. I would not be surprised if some guys from BC would use it when in the US... While most users will only be carrier squelch, it would not be unheard of to have PL on it.

 

[BlueDevil]

Thanks for your help. I will have to look into this. I am not really sure where to even begin. Our repeater is sitting on a mountain top in Southeastern Washington state at an elevation just over 5600ft. It can therefore probably easily pick up a station operating from elevation anywhere in Eastern Washington, Northeastern Oregon, North Central Idaho and the Idaho Panhandle. The signal I am picking up is either from a strong distant station or a weak close proximity station. It's a frustrating spot to be in!