Amateur Extra: Identifying in a Pileup

From the realm of “Good Operating Practice” we get our question of the week from the Amateur Extra exam. [E2C11]

How should you generally identify your station when attempting to contact a DX station working a pileup or in a contest?

A. Send your full call sign once or twice

B. Send only the last two letters of your call sign until you make contact

C. Send your full call sign and grid square

D. Send the call sign of the DX station three times, the words this is, then your call sign three times

The answer is, A. Send your full call sign once or twice.  This is the accepted, and polite, practice.  Repeating the last two letters of your call over and over (B.) until you finally get an answer might finally get a response, but you’ll just be walking over everyone else’s traffic in the process.  Sending your call sign and grid square (C.) might be effective, but its extra information that the DX doesn’t need, unless its part of contest rules or you’re actually carrying on a conversation.  In a pileup, though, its usually not needed.

Similarly, D. Sending the DX’s call 3 times with yours three times is way too much, and you’ll probably never get in, or you’ll just confuse the rest of the pileup into thinking you’re the DX! Not good.  Remember, short and clear.  If you hear the DX calling someone else, just wait your turn and be patient.

General: Increasing Inductance

This week’s General question comes from the section on circuit components. [G5C14]

Which of the following components should be added to an inductor to increase the inductance?

A. A capacitor in series

B. A resistor in parallel

C. An inductor in parallel

D. An inductor in series

The answer, is D. An inductor in series.  Neither A. A capacitor in series or B. A resistor in parallel will have any effect whatsoever on the inductance.  Adding an inductor in parallel will actually have an inverse effect.  Remember, that parallel inductance is similar to resistance, at least mathematically.

1/L = 1/L_{0} + 1/L_{1} + 1/L_{2} + ... + 1/L_{n}

In series, this becomes:

L = L_{0} + L_{1} + L_{2} + ... + L_{n}

Technician: Cause of Erratic SWR Readings

From the Technician pool today we look at a question relating to a common issue in amateur radio, SWR, or Standing Wave Ratio. [T9B09]

What might cause erratic changes in SWR readings?

A. The transmitter is being modulated

B. A loose connection in an antenna or a feed line

C. The transmitter is being over-modulated

D. Interference from other stations is distorting your signal

Remember the definition of SWR, which is the ratio of transmitted power, to reflected power.  Now lets examine each of the possible answers.

A. The transmitter is being modulated?  Well, not to put to fine a point on it, but this happens every time you key up.  Of course its being modulated.  Whether its AM (Amplitude Modulation), FM (Frequency Modulation), CW (Continous Wave) or SSB (Single Sideband) your transmitter is modulating a signal of some kind….

C. The transmitter is being overmodulated? Now, this is definitely a problem you don’t want to have, but it shouldn’t result in erratic SWR readings.  Instead you will get reports of distorted audio or harmonic interference, meaning your signal is “wider” in bandwidth than it should be.

D. Interference from other stations is distorting your signal.  “Intermod” is another one of those problems you don’t want, where signals can intermix inside your radio and cause strange problems….  but again, it shouldn’t cause erratic SWR readings.  That leaves us with…

B. A loose connection in the antenna or feed line.  This absolutely, positively will cause SWR problems.  The answer, then, is B. A loose or intermittent connection can show acceptable SWR one minute, then spike the next and back again.  This can potentially damage your radio, and cause RF problems in your equipment.

This is a good reason why you should have a SWR meter in your setup somewhere, if possible, and that you monitor it.

Amateur Extra: MPE Limits

The Amateur Extra question of the week has to do with safety, and Maximum Permitted Exposure (MPE) Limits. [E0A06]

Why are there separate electric (E) and magnetic (H) field MPE limits?

A. The body reacts to electromagnetic radiation from both the E and H fields

B. Ground reflections and scattering make the field impedance vary with location

C. E field and H field radiation intensity peaks can occur at different locations

D. All of these choices are correct

The answer is D. All of these choices are correct.  Let’s take a look at each one of those individually so we understand why.

A. The body reacts to electromagnetic radiation from both the E and H fields.  This means that your body reacts differently to electric and magnetic fields.  While the two are directly related, especially where RF is concerned, there are

General: Using Wind Power

Which of the following is a disadvantage of using wind as the primary source of power for an emergency station?

[G4E11]

A. The conversion efficiency from mechanical energy to electrical energy is less than 2 percent

B. The voltage and current ratings of such systems are not compatible with amateur equipment

C. A large energy storage system is needed to supply power when the wind is not blowing

D. All of these choices are correct

The answer is C. A large energy storage system is needed to supply power when the wind is not blowing.

Now, to be fair, this “disadvantage” is common to other similar generation methods, like solar.  If the sun’s not out, you’re not getting power, so you need some batteries to keep going.  If its all you have, then you go with it.

B. is inaccurate, as you could theoretically design a system that fits the voltage and current requirements just fine.  A. is just factually incorrect.  The actual number is probably somewhere between 30%-35% (http://www.mpoweruk.com/wind_power.htm)  And since we’ve already ruled out A and B, D. is therefore also incorrect.

Technician: Controlling Voltage in a Circuit

This week’s Technician question is another one where we can apply a little logic and the process of elimination…. [T6D05]

 

What type of circuit controls the amount of voltage from a power supply?

A. Regulator

B. Oscillator

C. Filter

D. Phase inverter

Well, first off lets just stop and think for a minute.  Control, control, control… what’s a synonym for control? Regulate! So, of course, the correct answer is A. Regulator.  But let’s look at the other options and see what they do.

An Oscillator doesn’t really control the amount of voltage from a power supply, rather it is responsible for shaping the waveform of the AC.  A Filter merely prevents or allows certain frequencies of electricity to pass through.  A Phase Inverter does exactly what you’d expect, it inverts the waveform of the power, so that instead of a high peak, you’d get a low peak, or vice versa.

Yet another example of a question that isn’t difficult at all, if you just slow down and think about it!

Amateur Extra: Non-linear Phase Response

Which of these modes is most affected by non-linear phase response in a receiver IF filter?

[E7C14]

A. Meteor Scatter

B. Single-Sideband voice

C. Digital

D. Video

The answer is C. Digital.  Why? Well, for one, the question is pretty vague.  If you’re using a Frequency Shift Keying (FSK) digital signal you probably won’t have any problems.  SSTV (D. Video) is a FSK mode.  B. Single-Sideband Voice doesn’t particularly care about phase at all.  And A. Meteor Scatter technically isn’t a “mode” at all, but rather a method of propagating the radio waves themselves.

However, if you are trying to transmit or decode a Phase Shift Keying (PSK) signal, then it only stands to reason that anything which alters that phase response in a way that is unexpected (like non-linear) will change encoding of the signal.  The end result will probably be unreadable.

General: 2m RTTY/Data Symbol Rate

What is the maximum symbol rate permitted for RTTY or data emission transmissions on the 2 meter band?

[G1C11]

A. 56 kilobaud

B. 19.6 kilobaud

C. 1200 baud

D. 300 baud

The answer is B. 19.6 kilobaud.  But why?  It has to do with the amount of bandwidth used by a signal.  1200 and 300 baud take up a very small amount of bandwidth, which is useful on the HF bands, but not so much on 2m.  You can still use these rates on 2m, but it isn’t required.  56kbaud would require too much bandwidth on 2m.

The reason for this goes all the way down to the wavelength of the signal.  In order to pack more symbols into a given space of bandwidth, you need smaller wavelengths.  HF wavelengths are relatively long, so you either need a larger bandwidth, or a slower rate to transmit the same number of symbols.  At higher frequencies, the wavelength shrinks, so you can fit more variance, and therefore more symbols, in a given passband.

Refer to 97.305(c) and 97.307(f)(5) for more information.

 

Technician: Tower Safety

The Technician class question of the week is from Section 0 (Safety.)  The answer to this question should be obvious, but we’ll go over it nonetheless. [T0B01]

When should members of a tower work team wear a hard hat and safety glasses?

A. At all times except when climbing the tower

B. At all times except when belted firmly to the tower

C. At all times when any work is being done on the tower

D. Only when the tower exceeds 30 feet in height

The correct answer, of course, is C. ALWAYS wear your safety glasses and hard hat while working on or around towers.  If you’re on the tower, you don’t want something in your eye or smacking you on the head to injure you, and possibly cause you to fall.  If you’re on the ground, you never know what might happen.  The climber may lose a tool, or a bolt or screw, and if you’re looking straight up at them….  And you never know when that antenna could come crashing down.

ALWAYS wear your safety gear.  Always.