Re: [IRCA] Broadband noise - (Getting rid of it)

[AM-DXer@xxxxxxxxx (Patrick Griffith, N0NNK / WPE9HVW)]

MOV (metal-oxide varistors) are rated in clamping volts, and joules of
power dissipation. They look like red thick disc capacitors with two
wire leads.
-------
Back in the late 70s I worked for a central station alarm company in
north-central IL. Since dedicated leased copper was becoming very
expensive, we installed a lot of digital dialers for residential and low
level commercial alarm systems. These required a direct connection to
the subscriber's telephone line. We would lose several devices to
induced voltages from every lightning storm that passed through the
area. Our equipment supplier had been experimenting with MOVs and
suggested that we place them across the two phone line leads (not to
ground) inside the alarm panels. This tremendously reduced our losses
due to lightning induced voltages. Of course they were no help in a
direct hit and we actually saw a few MOVs vaporized along with other
components. The next generation of alarm panels came with MOVs installed
at the factory. Since the MOVs were placed across the telephone lines, I
presume that their purpose was to equalize the potential on the two
lines rather than to drain it to ground.

Patrick Griffith
Westminster, CO
http://community.webtv.net/N0NNK/
http://community.webtv.net/AM-DXer/

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