Answer / sudhin r

Standing wave ratio (SWR) is the ratio of the amplitude of a
partial standing wave at an antinode (maximum) to the
amplitude at an adjacent node (minimum), in an electrical
transmission line.The SWR is usually defined as a voltage
ratio called the VSWR, for voltage standing wave ratio.
VSWR=Vmax/Vmin

Answer / sudhin r

Standing wave ratio (SWR) is the ratio of the amplitude of a
partial standing wave at an antinode (maximum) to the
amplitude at an adjacent node (minimum), in an electrical
transmission line.

The SWR is usually defined as a voltage ratio called the
VSWR, for voltage standing wave ratio. For example, the VSWR
value 1.2:1 denotes a maximum standing wave amplitude that
is 1.2 times greater than the minimum standing wave value.
It is also possible to define the SWR in terms of current,
resulting in the ISWR, which has the same numerical value.
The power standing wave ratio (PSWR) is defined as the
square of the VSWR.

Answer / gaurav sharma

Hi, If you feed an antenna with a signal a part of the
signal may reflect from the antenna and will return back to
the sender. This reflection only happens if the impedance of
your antenna does not match with the impedance of your
cable. So if your antenna is 50 Ohm and your coax cable is
75 Ohm, you will have a problem. The VSWR is a ratio that is
telling how well your system is matched and if the energy of
your transmitter is getting into your antenna. 1:1 is the
optimum and it means all energy made by your transmitter is
put into your antenna and nothing is reflected back to your
transmitter. if Your VSWR is 1:3 it still looks OK you may
think but now some 25% will return to your transmitter and
only 75% is put into your antenna.

If your VSWR is low it DOES NOT mean your antenna is good !.
. It only is telling its good matched. Every antenna also
has an efficiency, how much of the power put into the
antenna is effectively radiated by the Antenna. This is
expressed in dB. Mobile phone antenna's have normally an
efficiency of some -2 or -3 dB but their VSWR is 1:1.5 or
below which is very good

Explain 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?

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