In message <l81ap6+19csfea@...>, dated Sun, 8 Dec 2013, the_sky_falcon_1982@... writes:
It would be great if someone could shed some light on this problem.
GROUND 101
The problem is actually with the concept of 'ground', which is different in real life (and different there from what most people think it is) and what it is in Spice.
In real life, ground is simply a place assumed [*] to be at zero voltage, to which all other voltages are referred, and nothing to do with any planets or soil. Consider an aircraft, for example. Its 'ground' is probably the airframe.
While your transmitter and receiver are not electrically connected, their zero-voltage references could be connected together, without making any difference to their operation. This is good, because Spice will normally not work if a schematic has isolated circuits, not connected to anything else. Spice schematics must have a ground symbol (triangle) attached to the zero-voltage reference wire.
So for simulation purposes, you just add a fictitious connection between the 'grounds' of the transmitter and receiver. In a case where part of a circuit really has to have a high impedance relative to another part, you join its 'ground' to the other 'ground' via a high value resistor, but don't make it higher than necessary as this may cause convergence problems.
[*] Note 'assumed'. Other than superconductors, everything in real life has some impedance - resistance and inductance - so there can and will be a voltage between any two points on a 'ground' conductor that is carrying current. For correct operation, any such voltage must be so small as to be negligible. This can be done at low frequencies but when the dimensions of the ground are comparable with the free-space wavelength of the signal, such voltages will not be negligible.
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OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
