Blog Post #4 : Coupling vs Comb Filtering : The Conclusion!

Here we are at the concluding part of this series on “Coupling vs Comb Filtering “.

The three factors whose interactions we have been studying are :

2 Identical Signals.
Their Amplitude.
Their Phase.

In Part 1 we saw what happens when 2 Identical Signals of same amplitude interact with only phase as the varying factor. Then, In Part 2 we learnt what happens when we introduce an amplitude difference between 2 Identical signals and we also learnt to calculate the dB gain or loss associated with it.

We now know that the summed output varies depending on the phase and amplitude difference of the interacting signals and in this concluding part we will see all the factors come into play all at the same time and observe the resultant outcome.

Let’s have a look at the last slide from Part 2, which sums up all our calculations, showing the dB values of maximum summation and maximum cancellation at varies amplitude differences.

Effect of Amplitude and Phase Difference on the Summed Signal.

We will now verify this with our Simulated setup and observe the results on the analyser.

I’ll be restricting the text in this particular post of this series to the minimum and let the video do all the talking. So do watch the entire video for a complete understanding.

Check out the Entire Video on Part 3 below :

In the video above, we have verified the zone of maximum summation and maximum cancellation for different differences in amplitude and also that the comb filtering pattern remains within these constraints.

I call these constraints as : ‘Interaction Limit Boxes’!

I’m Posting a screenshot of these ‘Interaction Limit Boxes’ as a downloadable Image here, so you have it handy.

Interaction Limit boxes for Amplitude differences.Comn Filtering. — Interaction Limit boxes for Amplitude differences.

These interactions can be divided into 4 Major Situations :

Situation 1) A Win or Loose situation :

Maximum summation occurs when there’s 0 dB amplitude difference, but at the same time if there’s any amount of time difference, it will cause complete cancellation at that particular frequency depending on time delay.

Situation 2) When you win, you win good, but when u lose, the loss is considerable :

The >0 dB to 4 dB amplitude difference zone is the zone where the cancellations caused due to phase difference is really high, and we have a little less than 6 dB summation.

Situation 3) You neither win a lot, nor do you lose much :

The 4 dB to 10 dB amplitude difference zone is another zone where both the summation and cancellation are limited.

Situation 4) It doesn’t make a difference whether you win or lose :

The >10 dB zone is the zone where the summation and cancellations are almost negligible.

Remember these 4 things always as they are gonna heavily influence our System Design decisions.

Here, I conclude this series on Coupling and Comb Filtering, but this by no way means that we can now forget about this. We will always be referring back to this particular topic again and again and again.

So guys, go ahead and read all the three parts again, watch both the videos, try out different parameters and if you have any doubts whatsoever, let’s discuss and get them sorted!

Let us all be on the same page before we move forward on this journey of learning more on System Engineering.