Digital STL Interference Fix

Gotta watch those Fresnel zones!
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Jim Sofonia
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Digital STL Interference Fix

Post by Jim Sofonia » Mon Feb 09, 2015 10:42 am

I'm running two Mosley DSP-6000 links from downtown up to a relay tower that then sends these both N. and S. to distant sites. Some sort of interference was tearing up the digital lock on both services simultaneously, started over a year ago just a few seconds at first. But got up to minutes later. The relay tower has a 50kw FM on it. Turns out loose conduit, hoisting grips, and other metal near the receive STL dish were sparking as they make and break contact. Even the reflector elements of the Scala paraflector were doing this. I had the tower crew take up an AM radio tuned to no station and they could hear the static as they moved things around. We tightened clamps, added extra clamps till the radio was free of static. I also changed out the dish with one that I had the local welding shop bond all the reflector elements with a small weld to each. This probably applies to most any digital link. A third link on the tower that is composite was un-affected. Problem fixed!

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Deep Thought
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Re: Digital STL Interference Fix

Post by Deep Thought » Mon Feb 09, 2015 1:50 pm

This is also an issue for FM stations sharing space with cell sites...sometimes a huge issue depending on the politics of the tower site.
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grich
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Re: Digital STL Interference Fix

Post by grich » Mon Feb 09, 2015 3:47 pm

One of my sites had a hoisting grip break loose years ago and do exactly the same thing. STL dish was only a few feet away from the bottom of the FM antenna. Worst when the wind was hard from the NW...audio was completely trashed. The arcing burned a hole in the STL feedline jacket and ended up with water in the transmitter building sneaking along the inside of the jacket. The riggers dropped the STL dish fifty feet and all problems went away.

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NECRAT
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Re: Digital STL Interference Fix

Post by NECRAT » Tue Feb 10, 2015 6:49 pm

We had an issue with that at WWLP in Springfield where the side mounted FM (17kW @ 102.1MHz) near the top was getting into a loose cable on the tower, and was getting into our 2GHz microwave gear. If it was really windy outside, not only could you see the hits in the video, you could almost see them oscillate. After the tower crew strapped down the loose feedlines, the issue went away.
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Dale H. Cook
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Re: Digital STL Interference Fix

Post by Dale H. Cook » Wed Feb 11, 2015 7:07 am

Aaah - good old Provin Mountain. How long has WAQY been up there? Is their old site licensed as an aux?
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NECRAT
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Re: Digital STL Interference Fix

Post by NECRAT » Wed Feb 11, 2015 8:05 pm

Dale H. Cook wrote:Aaah - good old Provin Mountain. How long has WAQY been up there? Is their old site licensed as an aux?
[Quick Derail]
Easily been there 35 - 40 years, if not longer. Paul Donovan installed the "new" ERI up there in the early 90's, replacing an ancient 12 bay Phelps Dodge.
Before translators, pirates and 80-90 drop ins, you could hear them in a very large chunk of the Boston area with little effort.
They have an aux on their AM tower that was rebuilt in 2004, after lightning destroyed the old Gates antenna.
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