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Unusual sources of dropouts (Was: SRN News audio Dropouts)
To: CRTech <crtech@crtech.org>
Subject: Unusual sources of dropouts (Was: SRN News audio Dropouts)
From: Sherrod Munday <smunday@ieee.org>
Date: Fri, 10 Mar 2017 12:45:32 -0500
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References: <CAOkhgWpXdmgy4qs7cj4VQ8mV7o_SWOSm0eDHY53CpG-QLRz40Q@mail.gmail.com> <001301d299c1$41990190$c4cb04b0$@pilgrimradio.com>
On Mar 10, 2017, at 12:10, Bill Hurne <billhurne@pilgrimradio.com> wrote:
> Probably not the cause of your dropouts, but years ago I heard a short satellite dropout.   An idea popped in my head and quickly looked at the sky, and sure enough a jetliner had just flown through where the dish was pointed.   It crossed through the path to the satellite, between the dish and the satellite.   A few weeks later I witnessed the same thing happen.

Salem Radio Network's former Irving, TX location used to be directly on the flight approach path to the Dallas-Fort Worth airport.  When the wind was just right to make the planes approach from the east, they'd fly right over our building.  

We didn't just have dropouts from the sheer size of a full-size passenger jet going over our building at 1000 feet; their altimeter radars would also swamp the front-end of the LNBs.  I took an plain C-band LNB one day and plugged it into our spectrum analyzer and pointed it out my 4th-story window at the approaching aircraft, and watched as the noise floor swamped with each pulse of the radar as the plane got closer.  The LNB getting saturated meant that no receiver inside the building had a chance of receiving the satellite signal when the planes got close.

The resolution to that problem was a C-band bandpass filter from Microwave Filter Company.  (Dawnco now carries their filters for a better price.)   

-- 

Some of you may have heard about this other type of problem before, but many years ago I was working with a station in Alaska that was looking at the satellite at 87 degrees west to pick up a music format from Salem Music Network (where I worked at the time).  Their elevation look angle was something like 5 -10 degrees off the horizon because of how far west they are.

He told the story that one downlink in the area kept having brief dropouts, yet there was no pattern to them.  They finally figured it out when they were outside looking at things when a semi-tractor trailer drove by on the interstate not too far away from their property.  It seems their path to the satellite was shooting through a mountain pass, and the interstate went through that same path.  The trucks were just high enough to block the signal when they drove through the pass.

I have to say it's not too often we have to resolve "truck fade" in this business.  And that's a good thing.  :-)

--

And then there's the time that I had to help a station engineer with "cow fade" on his satellite dish... Suffice it to say that his dish was unprotected in the middle of a cow pasture, and the cows found a great tool at the perfect height to scratch their backs.  The poor mesh dish just couldn't stand up to a herd of 800-pound animals pushing on it.

I suggested that he might want to replace the dish and then invest in a simple fence around it.  Problem solved.

—
Sherrod Munday
<smunday@ieee.org>

Follow-Ups: Re: Unusual sources of dropouts (Was: SRN News audio Dropouts)
(Willie Barnett <wbradiolists@gmail.com>, 10 Mar 2017 18:03:28 -0000)
RE: Unusual sources of dropouts (Was: SRN News audio Dropouts)
("Bill Hurne" <billhurne@pilgrimradio.com>, 11 Mar 2017 19:38:48 -0000)
References: SRN News audio Dropouts
(Willie Barnett <wbradiolists@gmail.com>, 10 Mar 2017 15:05:29 -0000)
RE: SRN News audio Dropouts
("Bill Hurne" <billhurne@pilgrimradio.com>, 10 Mar 2017 17:10:54 -0000)
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