sustained oscillations created due to resonance in impedance match nertworks in recei

[lyndon237]

My project guide asked me the other day... "Resonance in the impedance matching network in your rf receiver circuit will create sustained oscillations. are these oscillations good or bad for the circuit?" I couldnt answer it... Please help me on this. Thank u

 

[JimB]

It sounds reasonably bad, but without a schematic and some context, who knows?

JimB

 

[lyndon237]

exactly! the worse part is that i am designing the receiver and the schematic has 2 be made by me... so it was just dumbfounding..!

 

[RadioRon]

If you have sustained oscillations in one of your receiver stages, it is usually very bad. When a stage oscillates, its output voltage swing is often limiting. This means that the oscillation is forcing the output voltage to traverse back and forth from its low voltage rail to its high voltage rail, or nearly so. When this is happening, the stage's through-gain is often quite poor and as a result, the entire receiver suffers reduced sensitivity. Another problem that may occur is that the oscillation causes a very high level signal to pass to following stages, especially if the oscillation is at the frequency of the receiver's IF or desired RF input as the oscillation output would pass through the receiver's filters. This will often cause the following stages to saturate as well, further reducing the sensitivity. The demodulator section may also be swamped by this oscillation signal and so become blocked from normal operation.

 

[lyndon237]

If you have sustained oscillations in one of your receiver stages, it is usually very bad. When a stage oscillates, its output voltage swing is often limiting. This means that the oscillation is forcing the output voltage to traverse back and forth from its low voltage rail to its high voltage rail, or nearly so. When this is happening, the stage's through-gain is often quite poor and as a result, the entire receiver suffers reduced sensitivity. Another problem that may occur is that the oscillation causes a very high level signal to pass to following stages, especially if the oscillation is at the frequency of the receiver's IF or desired RF input as the oscillation output would pass through the receiver's filters. This will often cause the following stages to saturate as well, further reducing the sensitivity. The demodulator section may also be swamped by this oscillation signal and so become blocked from normal operation.

Thanks a ton for that info. It would be of great help if u could amswer just one more question... when matching the impedance of the antenna to the receiver, resonance is bound to occur because we have to make the reactances of the antenna and reciver equal in order to cancel them out. Then will these oscillations that are set up affect the receiver? If so, what is the remedy?