Think of the symbol "Pi" (\(\pi\)). It's the same shape, with the two lines going down to the ground.

For a Low Pass function, the two capacitors will lead the higher frequencies to ground while opposing that path to lower frequencies. The inductor leads the lower frequencies to the output while opposing that path to higher frequencies.

Capacitors block DC

Also see Wikipedia article section and accompanying images: https://en.wikipedia.org/wiki/Antenna_tuner#Low-pass_π_network

Silly Hint: when I see the word "Pi", I imagine an excited child, he gets all excited, I want a capacitor and, and another and and! (it works in my mind, lol!)

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A capacitor has a response that increases as frequency increases and an inductor has the opposite response, it decreases as frequency increases. In the circuit described the inductor is between the signal path and ground and the capacitor in the signal path.

So, the capacitor impedes the passage of low frequencies in the signal path and the inductor allows the passage of low frequencies to ground leaving the higher frequencies as the only ones that pass through the T-network described.

Hint: a Touchdown pass is thrown HIGH

Another hint: Shunt rhymes with blunt which will make you high. Remember, folks, this is just a stupid mnemonic. DON'T DO DRUGS!

Movie Hint: Think of T-Rex as a HIGH dinosaur.

Yet Another: If you're Bri-ish, you enjoy High Tea!

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One of the most common issues with transmitting into a multi-band antenna system is the creation of harmonic distortion that can cause cross interference with the outgoing signal. Using some sort of filter network just prior to the last stage of the amplification process can suppress harmonics within that particular frequency transmission. Of these many different Filter Networks the Pi-L (π) network is one of the most effective methods to suppress the harmonics in the final stage.

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Hint: 4 "C's" Circuit + Complex = Cancels + Changes

The term “impedance matching” is rather straightforward. It’s simply defined as the process of making one impedance look like another. Frequently, it becomes necessary to match a load impedance to the source or internal impedance of a driving source. It’s crucial that the reactive components cancel each other. An example is the delivery of maximum power to an antenna. Impedances in radio-frequency transmitters must be matched to pass maximum power from stage to stage. Most impedance include inductances and capacitance that must also be factored into the matching process. Antenna impedance must equal the transmitter output impedance to receive maximum power.

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Chebyshev filters are analog or digital filters with a steep roll off at the edge of their passband and a ripple within the passband or stopband.

see: http://en.wikipedia.org/wiki/Chebyshev_filter

You can easily rule out two answers because op amps are active and LC filters are passive.

To rule another option out: "Butterworth filters are as smooth as Butter".

Another hint: "shev" looks like "shiv" which is slang for knife. And knives are sharp. Chebyshiv! (sounds like it could be the name of a mob boss)

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An elliptic filter (also known as a Cauer filter, named after Wilhelm Cauer, or as a Zolotarev filter, after Yegor Zolotarev) is a signal processing filter with equalized ripple (equiripple) behavior in both the passband and the stopband. The amount of ripple in each band is independently adjustable, and no other filter of equal order can have a faster transition in gain between the passband and the stopband, for the given values of ripple (whether the ripple is equalized or not). Alternatively, one may give up the ability to adjust independently the passband and stopband ripple, and instead design a filter which is maximally insensitive to component variations.

As the ripple in the stopband approaches zero, the filter becomes a type I Chebyshev filter. As the ripple in the passband approaches zero, the filter becomes a type II Chebyshev filter and finally, as both ripple values approach zero, the filter becomes a Butterworth filter. - K4AGO

https://en.wikipedia.org/wiki/Elliptic_filter

A key feature of elliptical filters is a sharp cutoff. Only one answer shows this.

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Hint:

Pi-L, L for inductance. So, its a Pi with an inductor. (jmsian)

Hint: It's the only answer that has "Pi" in it, which comes from the loose suggestion it looks like the Greek letter pi (π).

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A crystal lattice filter is A filter with narrow bandwidth and steep skirts made using quartz crystals.

Note: There is a slight difference in layout between crystal lattices and ladders. There are pairs of crystals within lattice networks. Resonance modes are paired with each crystal in the lattice that facilitate an intended bandpass envelope (shape) to pass.

As far as the "skirt" jargon - When viewed graphically, some filter transitions are said to resemble one or both sides of a woman's skirt, so sharp transitions are known as steep skirts.

Silly test tip: I just remembered this as, “Crystal likes to wear steep skirts.”

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A cavity filter is the best choice for use in a 2 meter repeater duplexer because it has a very high Q, can handle high power and is mostly stable to temperature changes. It provides a "steep" notch to only pass the band of interest with little loss.

The other answers given are worse choices because:

LC filters suffer from less than ideal L and C behaviors of their components.

Crystal filters typically cannot handle higher power.

DSP filters are not ideal because they would require analog-to-digital conversion which limits the power and requires regeneration of the signal (at a high power) after processing. Remember, DSP means digital signal processing, and a high power signal must be converted to low power digital then regenerated to be passed through DSP. A DSP filter would waste a lot of power and require more circuitry. They are mostly used when you start with a weak signal, then process it before sending it to a power amplifier.

https://www.amateur-radio-wiki.net/what-is-a-cavity-filter/ has an explanation of cavity filters and their use in amateur radio applications.

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From Wikipedia:

The Shape factor is the ratio of bandwidths measured using two different attenuation values to determine the cutoff frequency, e.g., a shape factor of 2:1 at 30/3 dB means the bandwidth measured between frequencies at 30 dB attenuation is twice that measured between frequencies at 3 dB attenuation.

This tells you how "sharply" and completely a filter attenuates signals outside of its passband.

The other answers don't relate to comparing signals inside and outside the passband.

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