The KCRC TechNet Puzzles For 2022

(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)

The KCRC TechNet Puzzle for June 8, 2022

Which formula is used to calculate inductive reactance?

A) Formula A.
B) Formula B.
C) Formula C.
D) Formula D.

The KCRC TechNet Puzzle for May 25, 2022

A moving-coil meter in conjunction with a bridge rectifier will measure alternating voltages. Such instruments are calibrated to read

A) the average value of a sine wave
B) the RMS value of a square wave
C) the average value of a square wave
D) the RMS value of a sine wave.

And now for the answer to our May 25, 2022 TechNet Puzzle

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

Most meters are calibrated for an AC’s ‘true’ sine-like shape (True RMS). These are more expensive than meters designed a calibrated to ‘assume’ that the waveform is a perfect sine wave (RMS). Root Mean Square (RMS) measurements are considered the ‘effective value of alternating current (RMS values reflect the amount of calories are released for heating devices. Therefore, these devices are calibrated for their RMS values for a given perfect sine wave (unless they are the more expensive ‘True RMS devices).

So, the correct answer is “D” the RMS value of a since wave.

The KCRC TechNet Puzzle for May 11, 2022

The mode of modulation that is least likely to cause problems of cross-modulation is

A) CW
B) FM
C) AM
D) SSB

And now for the answer to our May 11, 2022 TechNet Puzzle

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

This becomes easy as long as you know that cross-modulation is electrical intermodulation frequencies that are the sum and difference of nearby transmitting signals. This is very common in AM transmissions, as well as CW and SSB. Frequency Modulation (FM) changes its transmission frequency rather than the transmission amplitude. It has a unique ‘capture effect’ that can block most intermodulation distortion if one signal is stronger than others that are nearby.

So, the best answer is “B” FM.

 

The KCRC TechNet Puzzle for April 27, 2022

The circuit shown will:

A) pass frequencies below the cut off frequency
B) pass frequencies above the cut off frequency
C) pass frequencies above and below the cut off frequency
D) stop frequencies above and below the cut off frequency

And now for the answer to our April 27, 2022 TechNet Puzzle

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

Well, this question asks you to recognize the difference between a low pass filter (“A”), a high pass filter (“B”), a notch (band reject) filter (“C”), and a low bandwidth (high Q) band pass filter (“D”). I find that if I don’t recognize the circuit, I take a look at where the inductors and capacitors are arranged. Which are in series, and which are in parallel?

Low bandwidth passband filters require tuned LC circuits either in series to pass the frequency or in parallel to reject the frequency. The circuit above is a bit too simple to offer a low bandwidth resonant frequency, so “C” and “D” are unlikely candidates. Low pass filters usually have at their simplest, an inductor which blocks high-frequency current, in series and a shorting capacitor, in parallel, that shorts high-frequency current to ground. A high pass filter has a capacitor in series, passing higher frequency current through, while inductors, connected in parallel, short out lower frequency currents. The circuit above looks just like the low pass filter that I just described!

This circuit passes lower frequencies and shorts out higher frequencies – it is, by definition, a low pass filter, so answer “A” is the right one!

Logical, right?

 

The KCRC TechNet Puzzle for April 13, 2022

Which of the following are likely to assist in eliminating parasitic oscillations?

  1. Earthing the outer case of the equipment.
  2. Reducing the gain of the stage.
  3. Lowering the Q of the tuned circuits.

 

A) (1) and (2) only.
B) (1) and (3) only.
C) (2) and (3) only.
D) All of them.

And now for the answer to our April 13, 2022 TechNet Puzzle

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

Grounding your equipment will have no effect on any parasitic oscillations within your electronic circuits, BUT lowering the Q of tuned circuits and lowering the gain of amplifier stages might!

So, the best answer for this question is ‘C’ (2) and (3) only!

 

The KCRC TechNet Puzzle for March 23, 2022

Which one of the following statements about ground wave propagation is true?

A) It is at its strongest around mid-summer.
B) It carries amateur radio contacts on top band (1.8 MHz) in the daytime.
C) It increases during the hours of darkness.
D) It is the major means of propagation on the 14 MHz amateur band.

And now for the answer to our March 23, 2022 TechNet Puzzle

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

Ground-wave propagation is affected by the earth’s electrical characteristics and by the amount of diffraction around the curvature of the earth. These characteristics vary in different localities, but they’re relatively constant with respect to time and season. Sky-wave propagation is variable, since the constantly changing state of the ionosphere has a definite effect on the refraction of the waves.

So, what this question is inquiring about is when sky-wave propagation is worse and ground wave propagation is ‘the only game in town’.

The best answer is ‘B’ It carries amateur radio contacts on top band (1.8 MHz) in the daytime, because during the daytime, the D layer of the ionosphere absorbs most of the 1.8 MHz band, making skywave propagation at these times impossible.

So, the correct answer is ‘B’ It carries amateur radio contacts on top band (1.8 MHz) in the daytime!

 

The KCRC TechNet Puzzle for March 9, 2022

Why is the coil of a radio frequency choke (RFC) often wound on top of a resistor?

A) To provide a stable base for the windings.
B) To lower its Q factor.
C) To contain the magnetic field.
D) To increase its current earning capacity.

And now for the answer to our March 23, 2022 TechNet Puzzle

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

The usual reason an inductor is wound around a resistor is to deliberately make a poor (low-Q) inductor. At audio frequencies it acts as a piece of wire, as it has very low inductance. At medium radio frequencies the resistor loads the inductor. At high radio frequencies the presence of the resistive material within the inductor core ensures that it is lossy and so low Q. The net result is that it attenuates RF, but without having any serious resonances of its own. It stops parasitic oscillation. Quite often used in RF circuits, but less common in audio.

So, the correct answer is ‘B’ To lower its Q factor!

 

The KCRC TechNet Puzzle for February 23, 2022

What electronic devices have drains, gates, and sources?

A) triode vacuum tube.
B) full-wave rectifiers.
C) varicap diodes.
D) field effect transistors.

 

And now for the answer to our February 23, 2022 TechNet Puzzle

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

A triode vacuum tube has a plate, a cathode, and a grid.

A full wave rectifier has two AC inputs, and a + and – DC output.

A varicap (variable capacitor diode) has an anode and a cathode.

Only a field effect transistor (FET) possesses drains, gates, and sources.

So, answer ‘D’ field effect transistor, is the right answer!

 

The KCRC TechNet Puzzle for February 9, 2022

This is a half-wave dipole antenna. On which band will it resonate?

A) 7 MHz.
B) 14 MHz
C) 28 MHz
D) 50 MHz

And now for the answer to our February 9, 2022 TechNet Puzzle

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

We covered a very similar question a few months ago. If a half-wave resonant dipole is approximately 20 meters long, than the resonant frequency has a wavelength of approximately 40 meters – that is the 7 MHz Ham band.

So, the correct answer is ‘A’ 7 MHz

 

The KCRC TechNet Puzzle for January 26, 2022

Under which of the following circumstances may parasitic oscillation come about?

  1. on a particular setting of the antenna matching unit
  2. when using a particular antenna
  3. at a particular loading of the transmitter

 

A) (1) and (2) only.
B) (1) and (3) only.
C) (2) and (3) only.
D) All of them.

And now for the answer to our January 26, 2022 TechNet Puzzle

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

Parasitic oscillation is an undesirable electronic oscillation in an electronic or digital device. It is often caused by feedback in an amplifying device. The problem occurs notably in RF, audio, and other electronic amplifiers as well as in digital signal processing.

All of the above three problems can lead to parasitic oscillations, so, ‘D’ All of them, is the right answer!

 

The KCRC TechNet Puzzle for January 12, 2022

A product detector is used to:

A) limit RF output
B) demodulate SSB
C) remove harmonics
D) control an S meter

And now for the answer to our January 12, 2022 TechNet Puzzle

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

Regretfully, this is just something that you are aware of or not. There is little to ‘logic’ out the right answer, as far as I can see.

A product detector is a type of demodulator used for AM and SSB signals. Rather than converting the envelope of the signal into the decoded waveform like an envelope detector, the product detector takes the product of the modulated signal and a local oscillator, explaining its name. A product detector is a frequency mixer.

So, answer ‘B’ demodulate SSB is the correct answer!