Kenwood Analog repeater background noise in certain area of coverage where there was none before.

[Frmn85]

Hi fellow members,

I recently ran into a static issue in a certain area of a small facility that wasn't there before unitl after i performed measurements and made a minor increase in watt output. For the moment and I cant wrap my head around this. Maybe anyone here can offer some guidance.

The issue is a noticeable increase in static at a certain area( next to dispatch desk) that was apparently not there before until right after I checked measurements and swept the duplexer, and feedline. I increased the output power by .5 watts but reverted back after the issue came up in hopes to restore everything as it was before I came on site.

The static behind the audible communications is said to be like water and static mixed together. It is only heard on the downlink around the dispatch desk.

I used a VNA to sweep the area and only found a strong adjacent interfering signal about 2 MHz away ( to far away to cause issue right?). everything else was with in the noise floor. DL of repeater was at -95 or stronger ( good for analog) . No broadband noise of any kind was observed.



Below are some details.

The repeater is a conventional TKR840- 5 watt output and coupled with a BpBr Bird Duplexer and a single antenna.

Output of the repeater from duplexer to feedline is 2 watts.

Both are tuned to the best of its ability to meet their budget expectations. I want to note that
everything worked well after install, it is when i came back to check readings and made an attempt to optimize the system did things change reverting the minor changes did not cause the issue to go away.




Thanks for any guidance on this.

 

[RFI-EMI-GUY]

Can you test for desense?
Where is the repeater antenna located? Any electronics nearby?
Check the connections to duplexer, antenna, repeater.

 

[wd8chl]

Look for things that changed in or near that location, like a new computer or monitor, alarm equipment, or really anything electronic. Modern electronics generate noise. Computer networks are the worst. Very noisy.
I doubt there is an issue with the repeater. Oh, and to notice a difference in coverage, you need roughly a 3dB change. That means twice. If you're running only 2 watts, you would have to go to 4 to notice any change.

 

[rescuecomm]

If you disconnected coaxial fitting when making measurements, that should be checked.

 

[a417]

If you disconnected coaxial fitting when making measurements, that should be checked.

This.

That post reads as "It was fine till I touched it", and the point of order should be going back with a fine toothed comb to every component you touched. Something was disturbed, and the action of plugging / unplugging / moving / jostling is the primary causal factor here.

 

[Frmn85]

Thank you for the responses.
I sniffed the area for noise with a VNA and nothing came up in the area of interest. I will look into the duplexer tuning again and associated cabling next opportunity.



Hopefully it solves the issue.

 

[KevinC]

First place to check is the last place a human was.