Featured Post

High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

on
Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of
2

Propagation modes in radio communication

on
Propagation Modes::
· Ground-wave propagation
o Follows contour of the earth
o Can Propagate considerable distances
o Ground Wave = Direct Wave + Reflected Wave + Surface Wave
o At MF and in the lower HF bands, aerials tend to be close to the ground (in terms of
wavelength). Hence the direct wave and reflected wave tend to cancel each other
out (there is a 180 degree phase shift on reflection). This means that only the
surface wave remains.
o A surface wave travels along the surface of the earth by virtue of inducing currents in
the earth. The imperfectly conducting earth leads to some of its characteristics. Its
range depends upon: Frequency, Polarization, Location and Ground Conductivity.
o The surface waves dies more quickly as the frequency increases:

· Sky-wave propagation
o Signal reflected from ionized layer of atmosphere back down to earth
o Signal can travel a number of hops, back and forth between ionosphere and
earth’s surface
o Reflection effect caused by refraction
· Line-of-Sight propagation (LOS)
· Non-LOS propagation