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TV and other interference...
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pcs
Site master
Site master


Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post TV and other interference... Reply with quote
The rusty-bolt effect can be source of interference,
even when transmitter and receiver are perfectly fine.

Read on...

High-pass filters (at the television receiver aerial terminals) and low-pass
filters (at the transmitter) do not always cure TVI problems. Substitution
of other TV sets can generally show if the cause is a faulty transmitter or
faulty television receiver, but if substitution shows the interference
effect to continue, then the cause becomes more difficult to establish. The
''rusty-bolt" effect is one of the hardest of all these TVI causes to
locate.
If a known clean transmitter is causing interference to a known good
television receiver, then an external cause can be suspected. Perhaps the
transmitter signal is being picked up by a local conductor such as a
clothes-line or fence-wire. A rusty or corroded joint in this conductor may
be acting as a diode. Harmonics of the transmitter signal could be produced
by this spurious diode detector and re-radiated. These harmonics can be
received by the television receiver and cause interference to the picture or
sound.
Such interference may vary with the weather. It may be intermittent and be
affected by wind as well as rain.
Typical offenders are metal-tile roofs, metal gutters and down pipes. A
heavy blow with a hammer may sometimes correct an offending joint. Applying
water from a hose can sometimes change or remove the interfering source and
help to identify the culprit.
Either bonding or insulating the offending joint may solve the problem. More
than one joint may be causing trouble. Bonding is generally impossible with
metal tiles. Shifting the television aerial away from the offending harmonic
source or sources is a more practical cure. A bonded wire mesh over the
offending joint may be considered. It is unlikely that a complete metal roof
will have to be bonded to effect a cure.
Bonding suspect joints can sometimes produce problems. With bonded
conductors, a better signal pick-up may result, larger radio frequency
currents may flow, and the problem may shift to another joint that was
hitherto not suspect. Insulating the suspect joints may sometimes be more
effective. A change to nylon guy-wires may sometimes eliminate problem
joints.
The accepted rule is that if the offending joints are on the amateur's
property, the problem is his. If the offending joints are on the property of
the television set's owner the problem is his, Unfortunately, few set-owners
understand this problem and so the radio amateur should offer technical
assistance and advice. Re-siting the television set aerial or the
transmitting aerial is often the only practicable cure.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Fri Oct 15, 2004 2:23 pm View user's profile Send private message Visit poster's website
pcs
Site master
Site master


Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post Re rusty connections! Reply with quote
Apparently there was a situation in UK many years ago where an electric
heater with the old fashioned heating 'coils' was picking up radio waves.
Also a poor connection became a rectifying junction (something like an old
time crystal detector) and the metal of the heater became a sound box.
When some interference problems were being investigated the elderly lady who
owned the heater was asked why she hadn't mentioned or complained about it.
Her reply was that she enjoyed hearing the voices and the music that came
from the heater!

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Fri Oct 15, 2004 2:24 pm View user's profile Send private message Visit poster's website
voxlibertas
New registered user
New registered user


Joined: 04 Oct 2004
Posts: 1

Post Reply with quote
I am a little surprised dhe was not fined for having an untaxed reciever!
Fri Oct 15, 2004 11:07 pm View user's profile Send private message
pcs
Site master
Site master


Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post Reply with quote
Incredible things happen when you're close to a strong AM transmitter.

You can hear the signal from really amazing places. Phone and audio
amplifiers being the most usual.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Mon Oct 18, 2004 9:37 am View user's profile Send private message Visit poster's website
Sir Nigel
Moderator
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Joined: 28 Nov 2003
Posts: 334
Location: us.gif
us.gif

Post Reply with quote
What about one's ears? Or even from their jaw?

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Tue Oct 19, 2004 12:55 am View user's profile Send private message Visit poster's website
pcs
Site master
Site master


Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post Reply with quote
It has been reported from tooth fillings, indeed!

Now you need to live very close to am transmitter site.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Tue Oct 19, 2004 9:39 am View user's profile Send private message Visit poster's website
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