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Eliptical low pass filter simulation results discussed?

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neazoi

neazoi

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Hello, I simulated the filter described here.
https://www.zl2pd.com/SingleSpanOsc.html
The filter simulation gives much ripple throughout the hf band. Also it does not give any notch at 48mhz as the author states. What is wrong about my simulation?
Here is a screenshot.
 

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    sim.JPG
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What is your exact specification ?? I can check the components values...
 
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    neazoi

    neazoi

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I'm not an oscillator type but can tell you that the author has a typo in his design. I see the same thing.
FYI: I'm not familiar with with your simulation tool but notice that it says "Linear V".
untitled2.jpg
 
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    neazoi

    neazoi

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BigBoss said:
What is your exact specification ?? I can check the components values...
Click to expand...
the filter has to have 50R input/output. it has to be an LPF at 35mhz and has to have a deep notch at 48mhz as well

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ge said:
I'm not an oscillator type but can tell you that the author has a typo in his design. I see the same thing.
FYI: I'm not familiar with with your simulation tool but notice that it says "Linear V".
View attachment 77665
Click to expand...
look at the photo of the complete oscillator by the author http://www.zl2pd.com/img/SpanOsc/WideSpanOscFrontView.jpg
the little figure after the mixer shows the filter response he claims. LPF at 35mhz and a deep notch at 48mhz as well
 

To have a cutoff frequency at 35MHz and a deep notch at 48GHz, something has to give. Either there will be high ripple and poor return loss as in this design or a higher order filter or a combination of filters (LPF & notch).
 

neazoi said:
...it does not give any notch at 48mhz as the author states. What is wrong about my simulation?
Click to expand...
It looks like you're displaying the response with a linear vertical scale. Here's the result from my simulation, displayed both ways:




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ge said:
I see the same thing.
Click to expand...
You don't see the notch because you cut off everything below -30dB.
 
Last edited:

My point was that a higher order filter may be necessary. A 5th order filter will have poor return loss and > 2dB of ripple to achieve this slopeuntitled2.jpg. Maybe his design can tolerate this.

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Here is the results of a 7th order elliptical. The values look reasonable but I've not run a yield or optimization.
untitled2.jpg
 

These values seems to give reasonable results without changing the topology order
 

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