[CRTech] Christian Radio Tech [MSG 41550]
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Tom Brown=20

'Service with a Smile'

Gal. 5:13

-----Original Message-----
From: Michael [mailto:mbarnes@srnradio.com]=20
Sent: Friday, June 26, 2009 9:58 AM
To: CRTech
Subject: Re: [CRTech] satellite problem

Tommy Brown told me, On 06/25/2009 03:11 PM:
> Rookie Question...
>=20
> How does a LNB go bad?
>=20
> Tom Brown=20
>=20

An LNB can go through some pretty extreme temperature changes,
especially in the northern latitudes.  The difference between near or
sub-freezing temperatures and the intense heat by the focus of the sun's
rays warming to well over 100 degrees can cause significant expansion
and contraction of various components inside the LNB.  Different
materials react in different degrees of change.  Over time, due to these
changes, components can fail, joints come loose, component values can
change, etc.

So, it is really not unreasonable to expect failures in such a device
over time.

Typically, temperature changes over time will cause LNB failure.
However, an LNB uses highly sensitive circutry as that is the nature of
its purpose.  That also makes it susceptible to voltage spikes, signal
overloads, etc. which can "burn it out".

In very critical situations, the LNB is enclosed in an environmentally
stable radome to avoid these kinds of problems.

When I was CE of a station in Corpus Christi, I got a call they had lost
their downlink just before a live program they took at 2:30 pm.  By the
time I got everything loaded and made the 2 1/2 hour drive to the
station, everything was working fine.  I double checked everything and
went home.  Almost a week later, I got another call, same problem.  Same
routine, same results.   Another 3 or 4 days, same thing.  After some
questions, each day they had problems, it was a clear and hotter than
normal day.  Thinking the problem might be heat related, I took a couple
of halogen work lights out and put them next to the LNB for an hour.
The LNB got up to about 110 degrees, still working fine.  I went home
scratching my head.  A few days later, I packed up the camper and headed
up for my regular week long visit.  Finally, I was there when the
problem occurred. A quick check showed a very bright sun with a blinding
reflection onto the LNB. The outside surface registered 175 degrees!

I replaced the LNB, cleaned the scalar ring, wrapped some insulation
around the LNB and installed the long missing radome.  Never had a
problem since that I know of.

Michael



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