The KCRC TechNet Puzzles For 2023

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The KCRC TechNet Puzzle for December 13, 2023

Two types of coax are listed below. Which is/are balanced/unbalanced?

50 ohm coaxial cable                    75 ohm coaxial cable

A)     Balanced                                   unbalanced
B)     Balanced                                   unbalanced
C)     Balanced                                    balanced
D)    Unbalanced                               unbalanced

And now for the answer to our December 13, 2023, TechNet Puzzle

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

Whether a coaxial cable is designed for 50 ohm impedance for amateur radio, or 75 ohms for cable television distribution, all coaxial cables are unbalanced forms of transmission lines.

So, answer “D” is the correct answer.

 

The KCRC TechNet Puzzle for November 22, 2023

This is the circuit of a diode (envelope) detector of a receiver. What is connected to point Y?

A) The IF shift control.
B) The volume control.
C) The squelch.
D) The final IF transformer.

And now for the answer to our November 22, 2023, TechNet Puzzle

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

The signal detector gets its signal from the final RF stage of the radio’s receiver, and that would be the last IF (intermediate frequency) stage for the receiver – that would be the final IF transformer.

So, answer “D” The final IF transformer is the correct answer.

 

 

The KCRC TechNet Puzzle for November 8, 2023

What is the impedance at the center of a half-wave folded dipole antenna?

A) Approximately 15 ohms
B) Approximately 45 ohms
C) Approximately 150 ohms
D) Approximately 300 ohms.

And now for the answer to our November 8, 2023, TechNet Puzzle

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

Sorry, but you either remember this little fact or you are stuck guessing, if you remember that a folded dipole has a much greater impedance than a simple half wave dipole then, at least, you have a fifty-fifty chance of guessing right. If you remember that a folded dipole has approximately four times the impedance of a half wave dipole in free space, then you are much closer to your answer, as long as you also remember that a half wave dipole close to earth may have an impedance of approximately 50 ohms, but in free space that impedance is actually 73 ohms. Four times 73 ohms is 292 (near ground it goes down to somewhere above 200 ohms.

So, answer “D” approximately 300 ohms is the best answer.

 

 

The KCRC TechNet Puzzle for October 25, 2023

This circuit is a…

A) frequency multiplier
B) grounded grid amplifier
C) detector stage
D) balanced modulator

And now for the answer to our August 23, 2023, TechNet Puzzle

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

Let’s take a look around this schematic…

Gee… the vacuum tube’s grid is grounded! That sure narrows the best answer down.

This circuit shows an input being amplified by a triode, and having its high impedance vacuum tube impedance being transformed down to a nominal 50 ohms of impedance to be fed into an antenna. It would appear to not only be an amplifier, but a grounded grid type of amplifier.

So, answer “B” is the correct answer.

 

The KCRC TechNet Puzzle for October 11, 2023

Which of the oscilloscope traces above illustrates a morse code transmission?

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

And now for the answer to our August 9 2023 TechNet Puzzle

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

This should be relatively simple. Morse code is just a series of equal amplitude transmissions, just like “C” (shown displaying the letter “D”).

So, the correct answer is “C”.

 

The KCRC TechNet Puzzle for September 27, 2023

The simplest piece of equipment that can be used to test for the presence of harmonics in the output from a transmitter is:

A) a digital frequency counter
B) an antenna analyzer
C) an analogue multimeter
D) an absorption wavemeter.

And now for the answer to our July 26 2023 TechNet Puzzle

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

Now, this might be an unfair question for new Hams, since it goes a bit back into the history of Amateur Radio… Before there were such things as Vector Network Analyzers or even Spectrum Analyzers, there were much less expensive, far simpler devices known as Grid Dip Meters, which also worked as Adsorption Wavemeters. An Adsorption Wavemeter is just an adjustable, somewhat calibrated tuned circuit and a meter showing signal strength. One selected the proper range tuning coil, that also acted as the unit’s antenna, and twisted the sorta calibrated variable capacitor until it showed peak signal, then read the setting of the variable capacitors dial and you could tell approximately the frequency that it was receiving from the nearby transmitter! Viola! You could detect any strong harmonic above the designed frequency!

 

So, answer “D” an adsorption wavemeter is the right answer!

 

The KCRC TechNet Puzzle for September 13, 2023

To calculate the peak voltage of a sine wave, the r.m.s. voltage is:

A) multiplied by two
B) multiplied by the square root of two.
C) multiplied by 0.707
D) divided by the square root of two

And now for the answer to our September 13 2023 TechNet Puzzle

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

Sorry, but I can’t think of a clever shortcut. You just have to either know this or guess right.

By definition Vpeak = VRMS x √2, that’s answer “B”.

So, answer “B” – multiplied by the square root of 2 is the correct answer.

 

The KCRC TechNet Puzzle for August 23, 2023

The simplest piece of equipment that can be used to test for the presence of harmonics in the output from a transmitter is:

A) a digital frequency counter
B) an antenna analyzer
C) an analogue multimeter
D) an absorption wavemeter.

And now for the answer to our August 23 2023 TechNet Puzzle
(It is in “Invisotext” and will be visible if you highlight the area below!)

Sorry, but I can’t think of a clever shortcut. You just have to either know this or guess right.

By definition Vpeak = VRMS x √2, that’s answer “B”.

So, answer “B” – multiplied by the square root of two is the correct answer.

 

 

The KCRC TechNet Puzzle for August 9, 2023

What does this circuit diagram represent?

A) Down converter
B) Speech processor
C) Two-tone oscillator
D) Standing Wave Ratio meter

And now for the answer to our July 12 2023 TechNet Puzzle

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

Well, there is a simple way to answer this, and a more difficult one.

If you realize that the schematic shows two meters you can just guess which of the answers would require the ability to read forward and reverse currents. The only one is a Standing Wave Ratio meter. If you didn’t recognize that the meters were connected to indicate forward and reverse currents, just having two galvanometers that read two currents would be sufficient to eliminate the other choices.

So, answer D – Standing Wave Ratio meter is the correct answer!

 

 

The KCRC TechNet Puzzle for July 26, 2023

What is the cause of receiver blocking/ de-sensing?

A) Multiple reflections from the ionosphere.
B) The squelch control wrongly set.
C) The presence of a very strong signal on another frequency.
D) The core of a transformer is becoming saturated.

And now for the answer to our June 28 2023 TechNet Puzzle

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

The first stage of every radio – even Software Defined Radios – is a wide band RF amplifier stage. If that stage receives a very strong signal on another nearby frequency it will lower the amplifier’s gain, so as not to be saturated by the other strong signal. This will lower the receiver’s sensitivity to the frequency that you are trying to receive, at least until that other strong signal stops being received. This is also called “de-sensing” in the receiver.

So, answer “C” – The presence of a very strong signal on another frequency. Is the best answer.

 

The KCRC TechNet Puzzle for June 28, 2023

If a radio transmission is picked up on an antenna via both its ground wave and its sky wave, then the probable result is:

A) fading of the signal.
B) interference to adjacent channels
C) a decrease in the impedance of the antenna
D) an increase in the signal bandwidth

And now for the answer to our June 14 2023 TechNet Puzzle

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

 

Now, you may have to think about this a little while, but in the end it should make perfect sense.

 

Ground wave propagation is a much more direct route for your received signal. Sky wave involves at least one trip to the ionosphere and back, and sometimes multiple hops! The speed of light is a fixed thing in our atmosphere, so the longer the path, the more delayed the signal. That relatively short delay would not be problem, but you are ALSO getting that less delayed groundwave transmission and waves experience constructive and destructive interference – i.e “fade”. As the latency delay of your skywave interacts with your groundwave propagated received signal, the sum of the two signals will tend to re-enforce and attenuate the received signal’s strength!

 

So, answer “A” – fading of the signal. Is the best answer.

 

The KCRC TechNet Puzzle for June 14, 2023

A coax line is called unbalanced’ because:

A) the 2 conductors are not at equal potential
B) its impedance is lower than that of open-wire feeder
C) it only functions at certain frequencies
D) it has concentric wires

And now for the answer to our May 24 2023 TechNet Puzzle

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

Now, this might be a tricky question. “Balanced” antennas are recognized to be symmetrical – mirror images of the other side – i.e dipoles, Yagiis, etc. Open line, balanced transmission lines are similarly symmetrical, while coaxial cables with their single center connector and physically different surrounding braided conductor are not symmetrical in this way. In the case of coaxial cables the deciding factor that makes a coaxial cable unbalanced is that the surrounding braid is at ground potential, while the single center conductor is referenced to the shield’s ground potential. Balanced open line transmission lines are not required to be at ground potential on either of their two leads, The two leads have current flowing 180 degrees out of phase with the other wire and are both are refenced to the ground.

It may seem like a fine point, but that is the reason for coaxial cables being unbalanced transmission lines.

So, answer “A” – the 2 conductors are not at equal potential, is the best answer to this question.

 

The KCRC TechNet Puzzle for May 24, 2023

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 February 22 2023 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 May 10, 2023

The low pass filter in the microphone amplifier of a transmitter should cut off all frequencies above about

A) 3 kHz.
B) 6 kHz
C) 9 kHz
D) 12 kHz

And now for the answer to our May 10 2023 TechNet Puzzle

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

Generally speaking, most hams have limited their audio bandwidth, especially on SSB to 300 Hz – 2700 Hz, so anything past 3 kHz is not really doing anything useful.

So, the correct answer is “A” 3kHz.

 

The KCRC TechNet Puzzle for April 26, 2023

An SSB. transceiver, switched to lower sideband, is being bench tested into a dummy load. A 1 kHz signal is fed to the microphone socket.

If the display shows 3.700 MHz, the output frequency will be

A) 3.690 MHz
B) 3.699 MHz
C) 3.702 MHz
D) 3.730 MHz

And now for the answer to our April 26 2023 TechNet Puzzle

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

A 1 kHz signal will create two sidebands above and below the carrier frequency – 3.699 MHz AND 3.701 MHz, but this question only discusses the LOWER side band, which is 3.699 MHz.

So, the correct answer is “B” 3.699 MHz.

.

The KCRC TechNet Puzzle for April 12, 2023

A circuit contains only inductance and resistance. A voltage is applied. Then, after an interval of five time-constants has elapsed, the current will have

A) decreased to zero
B) reached one fifth of its final value
C) completed five complete cycles
D) attained a constant value.

And now for the answer to our April 12 2023 TechNet Puzzle

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

Just take a look at the puzzler from September 28, 2022! The current will rise asymptotically to near full current and remain there, as long as there are no voltage fluctuations in the circuit! Five-time constants long is time enough for this steady state to be achieved!

So, the correct answer is “D” attained a constant value.

 

The KCRC TechNet Puzzle for March 22, 2023

What is the component labelled X in this diagram?

A) Ferrite bead
B) Variable resistor
C) Varicap diode.
D) Radio frequency choke

And now for the answer to our March 22, 2023, TechNet Puzzle

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

 

Sorry, but you can’t ‘logic’ this one out. You either have to know the correct symbol for the right answer, or the correct symbol for all the wrong ones and choose based on elimination.

In this case, the schematic symbol indicated is a varicap. It shouldn’t be too hard; the symbol is half diode and half capacitor.

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

 

The KCRC TechNet Puzzle for March 8, 2023

A voltmeter is connected across points M and N. What will it read?

A) 0 V.
B) 15 V
C) 25 V
D) 35 V

And now for the answer to our January 11 2023 TechNet Puzzle

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

 

Okay, take a DEEP breath. This looks tough, but it really isn’t. This question is about resistor based voltage divider circuits – if you have a circuit with just two resistors in series, the voltage across the 1k ohm resistor will be different than the voltage across the 5k ohm resistor. The voltage across the 1k ohm resistor is 10 V and the voltage across the 4k ohm resistor is 40 ohms, but that doesn’t even matter. You are asked to provide the voltage difference from two IDENTICAL voltage dividers. That difference is always going to be ZERO, as long as you use identical voltage dividing resistor values!

So, the correct answer is “A” 0.

 

The KCRC TechNet Puzzle for February 22, 2023

During a typical 24-hour period, when does ionization have the least effect on radio signals?

A) Around midnight.
B) Just before daybreak.
C) Around noon.
D) Just after sunset.

And now for the answer to our February 22, 2023 TechNet Puzzle

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

Think of the ionosphere as an electrically charged layer of gas, charged by the solar winds and the cosmic rays of the Sun each day. When the Sun goes down the charging ends, but the ionosphere doesn’t immediately discharge all that energy – it dissipates it throughout the entire night, until the Sun rises once again in the East and the process starts all over again. According to this logic, the ionosphere is most discharged just before dawn.

So, answer “B” just before daybreak is the correct answer.

The KCRC TechNet Puzzle for February 8, 2023

A difference of about 700 Hz between Intermediate Frequency and Carrier Insertion Oscillator is needed to receive

A) SSB
B) AM
C) FM
D) Morse.

And now for the answer to our February 8, 2023 TechNet Puzzle

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

SSB, AM, and FM are all forms of modulated transmissions – i.e. their complex waveform contains information within them. CW, continuous wave used to convey Morse Code transmissions, is just a uniform carrier transmission – it is the pattern of the transmissions that provide its information – its dits, dahs, and spaces. Early wired teletype listened to the relay contact clicks, but Hams prefer a nice constant tone signal to recognize the patterns. By injecting signal 700 Hz different from the received carrier wave into a mixer, you can hear the difference – 700 Hz as an audio tone coming out of your receiver!

So, the answer “D” Morse Code is the correct answer!

 

The KCRC TechNet Puzzle for January 25, 2023

If the circuit shown here is inserted in the IF. path of a receiver, it will

A) improve the sensitivity of the receiver
B) remove spikes of interference.
C) decrease the bandwidth of the IF
D) prevent clunk’ in the loudspeaker at switch on

And now for the answer to our January 25 2023 TechNet Puzzle

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

 

These ‘reverse parallel diodes’ act as a protective circuit, shorting out any voltage higher than the voltage drop designed for these diodes (0.7 Volts for a silicon diode, 0.3 Volts for a germanium diode).

So, the best answer is “B”, removes spikes of interference.

 

The KCRC TechNet Puzzle for January 11, 2023

In which type of semi-conductor does the capacitance vary with changing voltage?

A) Zener
B) FET
C) Germanium
D) Varactor.

And now for the answer to our January 11 2023 TechNet Puzzle

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

 

Once again, the easiest way to figure out this question is to know what the choices are! A varactor is a variable capacitor diode – its capacitance varies with respect to the reverse voltage applied…

Zener diodes, Field Effect Transistors, and the element germanium don’t have that characteristic.

So, the correct answer is “D” varactor!