@MikeML the max square wave frequency is 50MHz and I am interested in the 11th or the 5th odd harmonic which would make it around 550MHz.

If you had posted this in your first post, this whole thread would have gone in a different direction....

One more question: What is the amplitude of the 50Mhz square wave?

 

I am sorry for that. The amplified square wave has a 4 Vpp amplitude.

 

I am sorry for that. The amplified square wave has a 4 Vpp amplitude.

That begs yet more questions:

What is the sensitivity of the spectrum analyzer at 550MHz?
What is the output impedance of your squarewave generator (or what impedance can it drive)?
Can you disconnect the normal load from the generator and temporarily replace it with a dummy load that has an equivalent load resistance?

 

I am not so sure what the sensitivity of the spectrum analyzer means I am using the R&S FS300 3GHz bandwidth analyzer.
The output impedance of generator is 50 ohm.
I am giving the signal from generator to my amplifier. Do you want me to replace the whole amplifier circuit with a resistor equal to Rin of amplifier?

 

Out of time today. I'll be back tonight. Maybe someone else can pick this up. I'm leaning toward a resistive attenuator that has a high enough input impedance so as to match the normal load on the generator, one that has a 50Ω output so as to match the cable and analyzer.

For example, a 40db attenuator could match the impedances and still leave enough signal so that the analyzer can display the 11th harmonic (sensitivity of the analyzer appears that it can resolve -110dbm).

 

@MikeML the max square wave frequency is 50MHz and I am interested in the 11th or the 5th odd harmonic which would make it around 550MHz.

Oops! That puts us in a different ball game altogether.

Why didn't you say that in the first place?

 

I didn't know this was going to be an issue sorry for that.

 

Ok. So you have a 50MHz square wave with 4Vpp amplitude. Why are you interested in the harmonic content?

 

...
The output impedance of generator is 50 ohm.
I am giving the signal from generator to my amplifier. Do you want me to replace the whole amplifier circuit with a resistor equal to Rin of amplifier?

Duh, it would have nice to know this in your very first post, too...

As the output impedance of the generator is 50Ω, then just disconnect it from what it normally drives and connect it directly to the 50Ω input on the analyzer using a meter or so of RG58A/U 50Ω coax cable.

The output impedance of the generator provides the required termination on that end of the coax, while the analyzer provides the termination on that end. Since the generator is designed to drive 50Ω, there is no issue.

Now if the generator could drive only a much higher impedance, we would have to do something heroic like a resistive pad or preamp...

 

I believe the OP is interested in the performance of an amplifier, not the square wave generator. The amplifier output may or may not be 50Ω. Who knows what it is.

Why he wants to measure the harmonic content at the output of the amplifier is still beyond me.

 

@MrChips you are right I want to analyze the output from amplifier not the output of my generator. Since it would be a measure of the integrity of my signal that at different frequencies the high frequency contents are also being amplified.

 

Why not just analyze the rise and fall time of the square wave output?

 

It is the requirement of project report to perform both time domain and frequency analysis.

 

What is the output impedance of the amplifier?