The KCRC TechNet Puzzles For 2024

(Click Here For TechNet Puzzles for 2017)

(Click Here For TechNet Puzzles for 2018)

(Click Here For TechNet Puzzles for 2019-2020)

(Click Here For TechNet Puzzles for 2021)

(Click Here For TechNet Puzzles for 2022)

(Click Here For TechNet Puzzles for 2023)

The KCRC TechNet Puzzle for February 28, 2024

The purpose of digitizing an analogue signal such as that from a microphone is to

A) limit the frequency response to between 300Hz and 3kHz.
B) identify the person who is speaking to comply with the license.
C) keep the ratio between the signal and background noise as low as possible.
D) allow the signal to be processed with suitable software.

The KCRC TechNet Puzzle for February 14, 2024

A long open wire twin feeder is feeding a dipole with a 20m signal. At a particular time and location on the feeder, the RF voltage is zero. Where else on the feeder at that time will the RF voltage also be zero?

A) At a distance of 5m further along the feeder.
B) At a distance of 15m further along the feeder.
C) At a distance of 10m further along the feeder.
D) At any distance further along the feeder

And now for the answer to our January February 14, 2024, TechNet Puzzle
(It is in “Invisotext” and will be visible if you highlight the area below!)

This question is about a signal with a wavelength of 20 meters. Waves go from their null intensity to its highest intensity, back to its null intensity, then to its lowest intensity, and end back at its null intensity.

Click this link to see image

So, the RF amplitude reaches zero twice, every 20 meter long cycle, OR once every 10 meters!!!!!

This means that answer “C” “At a distance 10m further along the feeder” is the correct answer!

 

The KCRC TechNet Puzzle for January 24, 2024

The circuit diagram shows an oscillator. The function of capacitor C relies upon the
ability of a capacitor to

A) prevent Direct Current entering further circuit stages.
B) prevent Alternating Current entering further circuit stages.
C) provide correct biasing of the transistor.
D) smooth alternating currents.

And now for the answer to our January January 24, 2024, TechNet Puzzle
(It is in “Invisotext” and will be visible if you highlight the area below!)

Oscillators can have dirty outputs. Their outputs can include noise, harmonics and DC currents, and most designers would prefer removing them. This particular circuit does not use the capacitor “C” as filter (that would need an inductor as well). Capacitors block DC, not AC, so answer B is incorrect. Capacitor C is after the transistor, so it couldn’t affect the transistor’s bias, so answer C isn’t correct. You might want to filter out noise and harmonics from an oscillator, but “smoothing alternating currents” is the last thing you want to do with an oscillator – oscillators are ALL about producing alternating oscillating output!

So, answer D is incorrect.
The only remaining answer is A, which is the correct answer!

The KCRC TechNet Puzzle for January 10, 2024

Rank these classes of amplification in order of their efficiency.

least most
efficient…………………………………… efficient

A) Class C                Class B                   Class A
B) Class B                Class A                   Class C
C) Class A                Class B                   Class C
D) Class C               Class A                    Class B

And now for the answer to our January January 10, 2024, TechNet Puzzle

(It is in “Invisotext” and will be visible if you highlight the area below!)

Unfortunately, you just have to know this (or be a great guesser). Class A amplifiers amplify signals through the entire wave. The are inefficient but require less filtering because they have less noise by-products. Class B amplifiers amplify only half of the signal waveform. They are more efficient than class A amplifiers but require more filtering of their outputs. Class C is the most efficient of these three class amplifiers. They only amplify a portion of half the wave form and require the most aggressive filtering of their output.

So, the answer “C” is the correct answer.