Sample questions from the Amateur Extra exam pool

Amateur Extra: Distance From Monitoring Facilities

Within what distance must an amateur station protect an FCC monitoring facility from harmful interference? [E1B03, 97.13]

A. 1 mile
B. 3 miles
C. 10 miles
D. 30 miles

The answer is: A. 1 mile.

Why? Because the FCC has said so, basically.  In section 13 of Part 97.

(b) A station within 1600 m (1 mile) of an FCC monitoring facility must protect that facility from harmful interference. Failure to do so could result in imposition of operating restrictions upon the amateur station by a District Director pursuant to §97.121 of this part. Geographical coordinates of the facilities that require protection are listed in §0.121(c) of this chapter.

 

Amateur Extra: Toxic Materials

Which insulating material commonly used as a thermal conductor for some types of electronic devices is extremely toxic if broken or crushed and the particles are accidentally inhaled? [E0A09]

A. Mica
B. Zinc oxide
C. Beryllium Oxide
D. Uranium Hexaflouride

The answer is C. Beryllium Oxide.  One of the hazards we face as radio enthusiasts is dealing with technology, and quite often the very materials we gain enjoyment from are also toxic if not handled with respect.  Beryllium Oxide is one of those.  So long as you don’t crush or cut the material, its pretty harmless.  The dust is what gets you.

I have run into a similar problem in antique radios I restore.  Occasionally I will run into a sheet of material acting as a vacuum tube heat shield.  You guessed it, its asbestos.  I simply remove the piece of material, very carefully, place it into a plastic zipper bag, and put it in the trash, taking great pains not to tear or crumple it.  It, too, is harmless if intact, but broken or torn it can release particles that could be inhaled and cause problems.

 

Amateur Extra: Estimating RF Fields

Which of the following would be a practical way to estimate whether the RF fields produced by an amateur radio station are within permissible MPE limits? [E0A03]

A. Use a calibrated antenna analyzer
B. Use a hand calculator plus Smith-chart equations to calculate the fields
C. Use an antenna modeling program to calculate field strength at accessible locations
D. All of the choices are correct

Lets examine all the possible answers and see if we can get the correct one by elimination….

A. Use a calibrated antenna analyzer.  This might tell you if you’ll be able to transmit through your antenna with a low SWR on a given frequency, but it won’t tell you anything about the radiation pattern and field strength.

(We just eliminated D. All of the choices are correct!)

B. Use a hand calculator plus Smith-chart equations to calculate the fields.  Much like A. Using a Smith chart won’t help you determine the RF fields coming off of the antenna.

The only way to estimate the RF pattern and field strength coming from an antenna or antenna system is to use software (or do it the very hard way!) to model the system and provide theoretical field values at given locations.

C. Use an antenna modeling program to calculate field strength at accessible locations is the correct answer.

(photo: https://commons.wikimedia.org/wiki/File:NEC_pattern_Helix_vgain.png)

Amateur Extra: ASCII Parity Bit

What is the advantage of including a parity bit with an ASCII character stream? [E8C12]

A. Faster transmission rate
B. The signal can overpower interfering signals
C. Foreign language characters can be sent
D. Some types of errors can be detected

The definition of a “parity bit” according to Wikipedia is: a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value one is even or odd. Parity bits are used as the simplest form of error detecting code.

Given the other answers don’t deal with error detection at all, its a safe bet that the answer is D. Some types of errors can be detected.

Amateur Extra: EME Communications

Which of the following digital modes is especially useful for EME communications? [E2D03]

A. FSK441
B. PACTOR III
C. Olivia
D. JT65

Due to the time it takes for signals to get to the moon and back, (EME = Earth-Moon-Earth) we need a mode that is highly dependent on time synchronization.  This way everyone knows when to transmit, and when to listen. D. JT65 is just that mode.

JT65 is a highly structured digital mode that requires the operator’s station computer to be synchronized to the world time servers.  Communications are then alternated at 60 second intervals, 47 seconds transmit, with 13 seconds for decoding.  Transmissions are limited to 12 characters, and the QSO follows a strict format of exchanges.

All of the other modes might be capable of making the EME trip, but all are independent of any external reference that makes them a reliable option.

 

Amateur Extra: Rectangular Coordinates

What do the two numbers represent that are used to define a point on a graph using rectangular coordinates? [E5C11]

A. The magnitude and phase of the point
B. The sine and cosine values
C. The coordinate values along the horizontal and vertical axes
D. The tangent and cotangent values

This might seem like a strange and really lame question, but I think the reason for it is to make sure you understand the difference between rectangular and polar coordinates.

In a rectangular coordinate system, the two numbers represent C. The coordinate values along the horizontal and vertical axes.  That might seem rather obvious.  For example, if you think of a checkerboard, for example, and measure over three squares, and up four, then those coordinates would be 3,4.

Polar coordinates on the other hand, are represented by a radius and an angle.  For example if you were to take a string and pin it to the center of the checkerboard, then rotate that string around the center, at a given length.  So if your string was 6″ long and it was at 90º from the horizontal, your polar coordinates would be 6∠90º.

See the image above for what this looks like.

Amateur Extra: Reactive Power in an Ideal Circuit

What happens to reactive power in an AC circuit that has both ideal inductors and ideal capacitors? [E5D09]

A. It is dissipated as heat in the circuit
B. It is repeatedly exchanged between the associated magnetic and electric fields, but is not dissipated
C. It is dissipated as kinetic energy in the circuit
D. It is dissipated in the formation of inductive and capacitive fields

First, recall the definition of reactive power.  Reactive power is mathematically there, but doesn’t really “exist.”  It arises from the complex or “imaginary” components of reactance that arise in a circuit with inductors and/or capacitors exposed to alternating current.

In an ideal circuit, that is one where the capacitors and inductors don’t have any resistive components, the power B. is repeatedly exchanged between the associated magnetic and electric fields, but is not dissipated.  Of course there are always resistive physical elements at play, and this power gets bled off in the form of heat, since a portion manifests as real or non-reactive power.

Since it does exist in mathematical terms, reactive power from one circuit can affect and interact with the reactive power in another circuit, such as how power grids interact.

Here’s a more in depth explanation of True, Reactive, and apparent power: http://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/true-reactive-and-apparent-power/

Amateur Extra: Op Amp Output Impedance

What is the typical output impedance of an integrated circuit op-amp? [E7G15]

A. Very low
B. Very high
C. 100 ohms
D. 1000 ohms

A A. Very low output impedance is a property of an IC op-amp.   In an ideal case, it would be zero.  But of course that’s never possible.

In reality, the behavior of an op-amp depends on the circuit that its in, and it can be used in many different types of circuits (see image above.)

The reason for the low impedance, is so that the voltage gain that is output by the device acts on the rest of the circuit, and not the op amp itself.  If the voltage output had to contend with a high impedance across the output terminals, The power would go there, instead of actually being output.

More information: http://www.learningaboutelectronics.com/Articles/Why-does-an-op-amp-need-a-high-input-impedance-and-a-low-output-impedance

(image: https://commons.wikimedia.org/wiki/File:Op-amp_circuits.jpg)

Amateur Extra: Sine Wave Odd Harmonics

What type of wave is made up of a sine wave plus all of its odd harmonics? [E8A01]

A. A square wave
B. A sine wave
C. A cosine wave
D. A tangent wave

Well, the answer to this question is mathematically somewhat complex.  The answer is A. A square wave.

Rather than try and explain the formulation, which involves Fourier series, I think that this video I found on YouTube demonstrates the results perfectly.

So why would we want to do this?  Well, for “digital” anything, we need as close an approximation to a square wave as we can get, in order to represent those ones and zeros, or on and off states.  Since our oscillator circuits can’t on their own generate a square wave natively, only a sine wave, we need to take several different oscillator harmonics and combine them.  Just like in the above video.

If you’re really interested, here’s a great explanation, math and all: http://www.mathworks.com/help/matlab/examples/square-wave-from-sine-waves.html

Amateur Extra: Satellite Mode Designators

What do the letters in a satellite’s mode designator specify? [E2A05]

A. Power limits for uplink and downlink transmissions
B. The location of the ground control station
C. The polarization of uplink and downlink signals
D. The uplink and downlink frequency ranges

Lets look at “mode designators” to understand what the question is about.  A mode designator is simply a letter that indicates what band to use when sending to (uplink) or listening to (downlink) a satellite.  For example, a U/U code means that both the uplink and downlink frequencies are in the 70cm band.  A V/U code means that the uplink is in the 2m VHF band, while the downlink is in the 70cm UHF band.

The answer then is D. The uplink and downlink frequency ranges.

Here is a list of mode designators:

Designator Band Frequency (General)
H 15 m 21 MHz
A 10 m 29 MHz
V 2 m 145 MHz
U 70 cm 435 MHz
L 23 cm 1.2 GHz
S 13 cm 2.4 GHz
S2 9 cm 3.4 GHz
C 5 cm 5 GHz
X 3 cm 10 GHz
K 1.2 cm 24 GHz
R 6 mm 47 GHz

Source: https://en.wikipedia.org/wiki/OSCAR#Mode_designators