RadioBanter - View Single Post

October 4th 03, 07:59 AM

wrote:

When will a wire radiate?

Whenever there is an alternating signal on it. The amount of radiation
that is detected will depend on the strength of the original signal and
the "efficiency" of the wire relative to the length of the wire in
relation to the applied frequency. If the wire is shielded, the
radiation will be much lower, perhaps to nearly undetectable limits
depending upon the type of shielding and the frequency involved. Yes,
the wires in your house radiate a signal at 60 Hz (60 cycles per second)
if you are in the United States or another country that uses the 60Hz AC
standard. Much of Europe uses a 50Hz standard. A wire with a DC current
flowing through it develops a magnetic field, but most people don't
characterize this as radiation, because most people tend to define
radiation at a specific frequency of interest for a particular
measurement.

A radiating wire is essentially an antenna. Typically, in popular use,
wires or equivalent metallic structures are not automatically considered
antennas unless they are intended to transmit or receive a specific
frequency range. This tends to increase confusion for people learning
about electromagnetic radiation.

Can we make an oscillator circuit to radiate by simply connecting its
output to a long wire ?

It already radiates, unless it is in a shielded box or enclosure. Of
course, the amount of radiation is typically pretty small unless it is a
very high power oscillator. Hooking a long wire to it may detune it and
cause the frequency of the oscillator to change, unless there is a buffer
amplifier between the oscillator and the wire. Again, the amount of
radiated signal will depend on the initial strength of the signal, and
the efficiency of the wire relative to the length of the wire in relation
to the frequency of the oscillator.

Where can I get suitable study material on net about the topic?

You might try searching for "rf fundamentals" or similar topics, which
will provide information about radiation in the Radio Frequency (RF)
regions. Other frequencies follow the same principles, but as long as it
is an alternating field, though the name may be different, essentially
the same effect is produced. As the frequency increases, there are some
interesting propagation effects (like, the received signal strength is
different for higher frequencies of the same power, given similar
distances, and reflections are more apparent at higher frequencies than
low ones, etc.,). There are tons of books about radiation in
relationship to antennas, so searching for "antenna fundamentals" or such
may also bring a bunch of information to light.

Good Luck
--Rick AH7H