How to deal with the “damping” problem a

[shengwuei]

Dear all,

I have a transmit/receive system which is functionally work but have “damping(?)” problem on the receive path.

A simple system block diagram as shown below, a small but not negligible “damping” waveform can be observed both before and after receive amplifier(cycled in red as the figure below, this problem become serious after the amplification of receive amplifier).

I am not sure this is a “damping” problem or not because the frequency of the waveform is much lower than transmitted signal(50MHz). I've added some series capacitor to filter out the waveform but found its useless. Possibly there is still some high frequency part(close to the transmitting frequency) inside the waveform so a simple low-pass filter would not work. I guess I need to find the root cause of the “damping” problem so I can make it totally disappear in the receiving path.

Really have no idea about how to solve this problem, anyone can give me a clue on it ?

Appreciated for your input.

 

[FvM]

Re: How to deal with the “damping” probl

I think, you should give some substantial information about the system.

Without it, I have to restrict myself to general considerations.

- You can check, if the unwanted signal is still oberserved when replacing the "transducer" with an equivalent load. If so,
you have proved, that the problem is most likely related to amplifier behaviour.

I assume, that the driving signal is clearly free of respective low frequency components and that no signal switching (hidden
in the diagram) is involved with the circuit.

- You have started another thread related to PA matching. If the "transmit amp" is actually a 300 W PA rather than a linear
amplifier, you should simply consider DC bias transients caused by the non-linear output stage. In this case, an effective
bandpass filtering should remove the problem.

P.S.: I don't think that the term "damping" is an adequate description of the observed transient signal.

 

[love_analog]

Re: How to deal with the “damping” probl

Most probably its the Tx leaking into Rx.

Need more information as pointed out by the other poster.