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 26, 2025

Increasing the number of turns on the secondary winding of a transformer will

A) increase the current output of the transformer
B) increase the power output of the transformer
C) have no effect on the transformer’s output
D) increase the voltage output of the transformer.

 

 

The KCRC TechNet Puzzle for December 11, 2024

A long perfectly matched open wire feeder is carrying a signal of wavelength 10m. At a particular instant in time the voltage at a point on the feeder is +10V. How much further along the feeder will the voltage be -10V at the same instant in time?

A. 10m
B. At the transmitter
C. Nowhere
D. 5m

And now for the answer to our October 23, 2024, TechNet Puzzle

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

10 meter waves reach null points every 5 meters. You can consider it with reference to its first null – at 0 meters, highest point at 2.5 meters, second null at 5 meters, lowest point at 7.5 meters, and another null point at 10 meters. The difference between the highest point and the lowest point is 5 meters!

That is answer “D”!

Because answer “D” is the correct one.

 

The KCRC TechNet Puzzle for September 25, 2024

Which graph shows the change in reactance of a capacitor as the frequency increases?

A) Graph 1
B) Graph 3
C) Graph 2
D) Graph 4.

And now for the answer to our June 12, 2024, TechNet Puzzle
(It is in “Invisotext” and will be visible if you highlight the area below!)

Sorry, you just need to know that at 0 Hz a capacitor has an infinitely high capacitive reactance, and it decreases as the frequency goes up.

That is Graph 2, so answer “C” is the correct answer.

The KCRC TechNet Puzzle for August 14, 2024

A sinewave with a Peak-to-Peak value of 22V will have an RMS value of approximately

A) 31V
B) 44V
C) 8V
D) 16V

And now for the answer to our August 14, 2024, TechNet Puzzle

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

What should come to mind is that square root of 2 number! Just divide the peak voltage by the square root to 2 and the answer is…

But wait. The question isn’t giving you the peak voltage. It is giving you the peak-to-peak voltage. That is TWICE the peak voltage. So, a peak-to-peak of 22V will have a peak voltage of 11V and dividing that by the square root of two gives you 7.857142857142857…

Let’s round that off to 8V.

That is answer “C”!

Answer “C” is the right answer.

The KCRC TechNet Puzzle for June 12, 2024

Batteries have a physical property known as their ‘internal resistance’. One effect of this is to

A) increase the EMF of the battery in proportion to the current drawn
B) act as an independent parallel resistance to the load on the battery
C) increase the voltage potential difference at the battery terminals as more current is drawn
D) reduce the voltage potential difference at the battery terminals as more current is drawn.

And now for the answer to our May 8, 2024, TechNet Puzzle

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

Internal resistance acts as a series connected resistor right before one of the battery’s connectors, so answer “B” is wrong. A resistor serially inserted to a circuit will act as a voltage divider. The more current the battery uses, the larger the voltage divider will drop the voltage after the internal resistance.

Gee, that is answer “D”!

That is appropriate, since “D” is the correct answer!

 

The KCRC TechNet Puzzle for May 22, 2024

What is the main reason for a switched mode power supply to operate internally at a frequency well above 60Hz?

A) To provide a much faster switch-on rather than waiting for capacitors to charge.
B) To allow a digital control system to be used providing enhanced control features.
C) To allow a much smaller and lighter transformer to be used.
D) To minimize the risk of unwanted radiation into the equipment or mains supply.

And now for the answer to our April 24, 2024, TechNet Puzzle

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

The benefits of switched mode power supply are that they are lighter, usually less expensive, and more efficient. This is all because they require a much smaller, less expensive, and more efficient transformer AND this is due to the fact that the transformer isn’t dealing with a low frequency 60 Hz power source, but a power source alternating at a frequency in the kilohertz range.

Or, in other words, “To allow a much smaller and lighter transformer to be used”, which is answer “C”…

So, the best answer is “C”.

 

The KCRC TechNet Puzzle for April 10, 2024

The circuit shows an amplifier biased in

A) class A.
B) class B.
C) class AB.
D) class C

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

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

The output shows the ENTIRE input waveform. Class “A” amplifiers do that! Class “B” only show half of the original waveform, Class “AB” shows more than half, but less that all the original waveform. Class “C” shows even less than half of the original waveform.

Clearly, in this question, the correct answer is “A” – Class A.

The KCRC TechNet Puzzle for March 27, 2024

Components in a tuned circuit may need high voltage and current ratings because:

A) inductors and capacitors generally become less effective as they get older.
B) most tuned circuits are used with vacuum tubes which require high voltages.
C) high voltage and circulating currents may exist when the circuit is operated at
resonance.
D) the voltage across the capacitor and inductor will add in phase.

And now for the answer to our March 27, 2024, TechNet Puzzle

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

Tuned circuits use a fascinating concept: resonance. Resonance allows energy to be efficiently stored over a short period of time. Resonant circuits possess a “Quality Factor” designated “Q”. The quality factor is the ratio of the voltage across the inductor or capacitor to the voltage in a resonant circuit.

Gee, that sounds like answer “C”. That’s because answer “C” is the right answer!

 

The KCRC TechNet Puzzle for March 13, 2024

A variable inductor is set to its maximum value and connected in series with a
capacitor to form a tuned circuit. As the value of the variable inductor is decreased
the effect will be that the

A) resonant frequency will increase.
B) impedance at the resonant frequency will increase.
C) resonant frequency will decrease.
D) reactance will increase

And now for the answer to our March 13, 2024, TechNet Puzzle
(It is in “Invisotext” and will be visible if you highlight the area below!)

Sorry, but you’ll need to know what the formula for determining the resonance of a tuned circuit is:

For illustration click this link!

You will notice that as you lower the capacitance or the inductance the frequency will increase and vice versa!

The question asked what would happen if you lowered the inductance, so answer “A” – “resonant frequency will increase” is the correct answer!

 

The KCRC TechNet Puzzle for February 28, 2024

The purpose of digitizing an analog 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.

And now for the answer to our February 28, 2024, TechNet Puzzle

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

Modern day radios benefit from Digital Signal Processors (DSP) to remove noise from the received signals. DSP do require a digitized signal to do their “magic”, and this is why the audio stream must be digitized from its analog signal into a digitized one, to let the DSP work!

Therefore, answer “D” is the right answer!

 

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.