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.

 

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)

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.

 

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/

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