{Collins} Re: 30L-1 upgrade - TVI question

Computer speakers are really weird!  I do not get into
any of the speakers connected to my computers
including the speakers on the computer in the radio
shack that are located within 2 feet of my linear.

My next door neighbor (who is a computer consultant
and works out of his house) has numerous speakers all
over his house and there is a single speaker that I
sometimes get into when running SSB on 75 meters.  I
have offered him ferrite to put on it but he says that
when I do get into the speaker he just unplugs it.

Years ago there was a neighbor a couple of houses down
the alley that I got into his hifi system.  I added
0.001 mfd capacitors from all of the speaker leads to
ground on his hifi amplifier and the problem went

Telephones are a different matter.  Several years ago
the FCC did a study of interference to telephones
which involved transmitters from legal 4 watt output
Class "D" Citizen's Radio Service stations to a
500,000 watt output shortwave broadcast station.  They
found that if fully bypassed/filtered telephones were
installed that in all but a single case the
interference problem was solved.  Such telephones are
manufactured (actually existing models of telephones
are modified) by several companies.

The "el cheapo" import telephones and cordless
telephones were the most likely to have interference
from nearby transmitters.  It was discovered that the
old AT&T 2500 model sets (those "Touchtone" sets with
the square face that were most common in the late
1960s through 1980s era) were the best telephones
where interference was concerned.  Those model
telephones were very unlikely to have problems and
when they did have problems adding bypass capacitors
across the ear piece and microphone cartridge as well
as adding bypass capacitors from each side of the line
to ground would usually cure any interference even
from high powered shortwave stations.

The FCC came to the conclusion that the telephone
industry was its own worst enemy where r.f.
interference was concerned.  I wrote an article that
was published in 73 Magazine not that long before the
magazine went out of business about this.  Frankly, I
do not remember the exact issue in which this was
published.  Also, somewhere in my files I have a
couple of copies of the official FCC report on
telephone interference.

The report was not that widely circulated.  I found
out about it from a "blurb" in a BICSI newletter and
obtained a copy for my records.

There are occasionally problems with fiber optic
systems.  It is not in the fiber itself but is in the
electronics that convert the telephone audio and
television video/audio so that it will work with
consumer equipment.  I have "fiber to the brick"
(there is an optical fiber that comes all the way to
my house) with a conversion unit located on the
outside wall of my house (all of Richardson, Texas,
now has this for telephone service - by AT&T - and
fiber television is now available as well).  That box
is just on the other side of the wall from my main
operating console.  I had to install bypass capacitors
on "my side" of this conversion box to keep r.f. from
causing problems.

Now the electronics are well shielded in the
conversion box.  However, r.f. was being conducted
into the electronics by the copper lines to the
telephones inside the house and by the Cat 5e line
that runs to the hub that sits right beside my main
computer monitor for fiber Internet and for fiber
television service (which replaces the cable
television service that I had before fiber became

Glen, K9STH

--- Roger Shultz <nj2r@xxxxxxxxxxxxx> wrote:

I've never gotten into any TV's, but cordless phones,
some Klipsch sub-woofers (not Bose), cheap computer
speakers, and even the controller of my wireless alarm
system have all been fair game for high power RF at
one time or another. Filters or ferrite chokes usually
took care of the problem except for the Klipsch
sub-woofer in it's unshielded cabinet.
The 30L-1 is one of the best and cleanest amps of all
time and will not in itself cause a problem. The
problem lies on the Part 15 consumer electronics end.
As cable systems convert more and more to fiber, TVI
should be thing of the past.

Glen, K9STH

Website:  http://k9sth.com

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