RAE mock exam

Providing training material and marking the papers

The SARL supplies study material, appoints the invigilators and marks the papers, but licences and callsigns come only from ICASA.

CQ DX CQ DX de ZS6XYZ ZS6XYZ K

In Morse, 'de' comes before your own callsign and K invites any station to reply, whereas KN invites only a station already called; phonetics are never sent.

An online contact confirmation system

LoTW is the ARRL's online system that matches uploaded logs from both stations to confirm contacts electronically.

A contact between two amateur radio operators

QSO is the Q-code term for a contact between two amateur stations.

Hotel Oscar Romeo November

H is Hotel, O is Oscar, R is Romeo and N is November; Ocean and the other words are not in today's alphabet.

23:30Z on 4 March

SAST is two hours ahead of UTC, so going back two hours from 01:30B crosses midnight and gives 23:30Z on the previous day, 4 March.

Working as many different stations as possible in a fixed time

Contesters race to work as many different stations as they can before the contest period ends; entry categories let similar stations compete.

October of the same year

According to the manual there are two sittings a year, in May and October, each on the third Saturday.

Follow the talk for a while, and call in only if you have something to add

Listen to learn what is being discussed and join only if you can add something useful to that topic; steering the talk elsewhere hijacks their conversation.

Contact 100 stations in South African regions

The Worked All ZS award needs contacts with 100 different stations spread across South Africa's regions.

10 seconds

An hour is 3 600 seconds and 3 600 ÷ 300 = 12 seconds per contact, so 10 seconds is the nearest option.

To continue communication during power outages

Batteries, generators or solar power keep a station on the air when mains power and telephones fail in a disaster.

Considerate and loyal

The Code of Conduct opens by saying the amateur is considerate and loyal, followed by progressive, friendly, balanced and patriotic.

ITU

The ITU allocates radio spectrum and satellite orbits worldwide; ICASA manages spectrum only within South Africa.

QRL?

QRL? means 'Are you busy?', and on CW it is how you ask whether a frequency is already in use before you call.

Move to another clear frequency and talk direct

Calling frequencies and repeaters are shared, so a long one-to-one chat belongs on a clear simplex frequency; long group chats that anyone may join are a different matter.

Exchange signal reports to check that you can copy each other well

Early signal reports show whether both stations can copy each other; if not, a long conversation will only frustrate you both.

QSL?

QSL? asks 'Can you acknowledge receipt?', and the reply QSL means 'I acknowledge receipt'; QRK? asks how readable your signal is, not whether it was received.

IARU

The IARU was formed to be the voice of radio amateurs internationally, and the ITU recognises it as their representative at its conferences.

Drop out for now and try again from a better place

If you cannot reach the repeater properly, sign clear and try again from a better position instead of wasting everyone's airtime.

Model it with antenna design software

Antenna modelling software shows how a design should perform, so changes can be tried before any money is spent on building it.

ICASA

Licences and callsigns come only from ICASA, the licensing authority; the SARL supports amateurs but issues neither.

That they can set up and operate an HF amateur station

Class A candidates must also show in a practical assessment that they can install and operate HF amateur equipment; Morse code is not required.

By helping the amateur deal with the planning problem and the authorities

The SARL supports amateurs who run into local or regional building regulations, assisting them with the authorities; it has no power to approve plans itself.

More than 100

Radio amateurs have launched more than 100 small communications satellites for amateurs around the world to use and learn from.

To the QSL manager, not to the station

A QSL manager handles a busy station's cards for it, so send yours to the manager; a card sent to the station itself will almost certainly go unanswered.

They make operating easier and reduce congestion

Band plans are mostly voluntary agreements, drawn up with every amateur's interests in mind, that make operating smoother and cut congestion.

By your own judgement of how strong the signal sounds

The strength figure is a subjective judgement of how strong the signal sounds; an S-meter reading can guide you but does not set the report.

Check the antenna, the reflected power and the frequency

Never assume the old settings are right; check that the antenna is in order, the reflected power is low and the frequency is correct.

By linking the vehicles, reaching a home base and calling for help if needed

In empty country, amateur radio keeps the vehicles of a party in touch, links them to a home base and can summon help in an emergency.

A soundcard interface

A soundcard interface for a computer is simple enough to build in a single evening.

Say things in ordinary words that everyone understands

The aim is clear communication, so speak plainly; slang meant to keep outsiders guessing only confuses other amateurs too.

So that confirmations are very hard to forge or alter

A confirmation is worthless if it can be forged, so it is signed with a secret key; anyone can check it, so it is not about secrecy.

A scheduled time and frequency to meet another amateur

A sked (schedule) is an agreed time and frequency at which two amateurs plan to meet on the air.

Stay off the air unless you can supply something they lack

Keep quiet unless you can fill a real gap, such as a working telephone, and leave it to the station in charge to accept your help.

ICASA

ICASA, the national statutory regulator, plans, assigns and manages the radio frequency spectrum in South Africa.

On every transmission, that is, every over

The law requires you to identify on each separate over, so giving your callsign only at the start and end of a contact is not enough.

A continuous sub-audible tone (CTCSS)

A CTCSS tone squelch keeps the repeater shut until it hears a continuous sub-audible tone, often 88,5 Hz; sending your callsign in Morse would not open it.

The IARU Region 1 plans, shared with Europe

Africa lies in ITU Region 1 together with Europe, and IARU band plans normally cover a whole region, so South Africa keeps to the Region 1 plans.

Transmitting music for entertainment

Music may be sent only under very specific conditions (the ICASA band plan allows it on a few bands), never as entertainment broadcasting; contacts abroad, digital modes and Morse are all allowed.

Cabinet radiation, cured by better screening

Stray currents inside a badly designed cabinet radiate directly, bypassing the antenna socket and any filter there; the cure is better screening, a Faraday cage round the transmitter. Matching the antenna does nothing for it.

The flow in equals the two flows out added together

Water cannot pile up in the T, so the flow in equals the two outlet flows added, like current at a junction. None is used up in the connector, as no current is lost at a junction.

About 230 V AC at 50 Hz

South African mains is AC at 50 Hz; its nominal voltage is now 230 V, though the manual still gives 240 V. 60 Hz is used mainly in the Americas.

RF interference, often across the HF bands

Their fast square-wave switching can spread strong RF interference over the HF bands and beyond, a real problem for amateurs, although well designed and shielded supplies need not interfere. Mains hum comes from ripple.

Zero, as the two reactances cancel

At resonance XL and XC are the same size with opposite signs, so XTotal = XL − XC = 0; the frequency where this happens is the resonant frequency. An unlimited reactance belongs to an ideal parallel circuit.

In the same place as for the USB signal

For USB and LSB alike, the LO goes where the suppressed carrier would be and recovers the audio; only the side on which the sideband lies differs. An LO 3 kHz lower would turn the audio upside down.

1,6 A

The internal resistance is in series with the load, so I = VS ÷ (RSource + RLoad) = 4,8 ÷ 3 = 1,6 A. Leaving out the 0,8 Ω gives 4,8 ÷ 2,2 = 2,2 A.

10 dB

RV = 6 ÷ 2 = 3 and 20 log₁₀ 3 = 9,5 dB, as the power rises nine times, so 10 dB is nearest; 10 log 3, about 5 dB, treats RV as a power ratio.

Smaller, cheaper and much of their work automated

The manual lists digital circuits as smaller and therefore cheaper, free of sensitive adjustment, robust, largely automated and updatable by software. Lower power use is not among its claims.

It stays at 90°

The current and voltage of a capacitor are always 90° apart, whatever the frequency; only the reactance changes. Doubling to 180° would make them exact opposites, which no change of frequency does.

2:1

NP ÷ NS = √(RP ÷ RL) = √(200 ÷ 50) = √4 = 2, so 2:1. A 4:1 turns ratio would raise the 50 Ω to 4² × 50 = 800 Ω, since impedance follows the square.

Almost every one does, at least on its own transmit bands

Because of these advantages, nearly all modern amateur transmitters can also receive, at least on their own bands, and many add general-coverage receive. Separate units were the rule only in the early days.

Quite high, like a current source

Collector current is set by the base and hardly depends on collector voltage, so the collector behaves as a current source of fairly high impedance; L1 also has high reactance. Low output impedance is the emitter follower’s.

It is the lead with the arrowhead

The emitter is always the lead with the arrowhead. Symbols may be drawn either way round, and the manual’s own NPN and PNP drawings put the emitter on opposite sides, so position tells you nothing.

The ear is insensitive to very short gaps in sound

Human hearing barely notices very short interruptions, so losing the wanted signal for that moment costs far less than hearing the spike. The AGC only sets the gain; it cannot fill in missing audio.

Negative feedback

Any drift of the VCO produces a comparator voltage that pushes it back the other way, which is negative feedback. Positive feedback is what makes an oscillator start and keep oscillating.

27 mA

I = V ÷ R = 15 V ÷ 560 Ω = 0,026 79 A = 26,79 mA, so 27 mA is nearest; 2,7 mA and 270 mA misplace the decimal comma, and 37 A divides 560 by 15.

The total gain a signal gets on one trip round the loop

Loop gain is the overall gain from any point, once round the loop and back: the amplifier’s gain less every loss, such as the output take-off and the phase-shift network. The amplifier alone is only part of it.

Signals on the image frequencies

Ahead of the mixer, the filter keeps out image signals on the far side of the LO, which would also convert to 28-30 MHz. The sum product appears only after the mixer, where the 28-30 MHz filter removes it.

1 950 kHz

The LO is at 1 040 + 455 = 1 495 kHz, and the image one IF above it, at 1 950 kHz, in the 160 m band. 1 495 kHz, f + IF, is the LO itself.

About 11 years

Solar activity rises to a maximum about every 11 years, with a minimum in between. Seven or eight years is the manual’s figure for the fall from a maximum to the next minimum, not the whole cycle.

The series-tuned Colpitts

In the Clapp the tuning capacitance sits in series with the coil, so the manual calls it a series-tuned Colpitts; its VCO and crystal circuits both use it. The ordinary Colpitts has a parallel tuned circuit.

Its distortion mixes the signal’s many frequencies into unwanted products

A multiplier works by distorting its input, and the many frequencies in an SSB signal then mix into products too close to filter out (pp153 and 173). The missing carrier is not the reason.

Wirewound resistor

Wirewound resistors are made for high power ratings in DC circuits, from about 2,5 W up to 20 W and beyond. Carbon film resistors stop at about 2 W, and metal film and network resistors are low-power parts.

Let the carrier rise and fall gradually, not switch instantly

Softening the keying edges, with a rise and decay of a few milliseconds, removes the high harmonics that cause clicks. Switching faster makes the edges harder still and the clicks worse.

The transformer principle

The manual calls it the transformer principle: the primary and secondary voltages are in the ratio of the turns, VP ÷ VS = NP ÷ NS. Ohm’s law relates voltage, current and resistance in one component instead.

It passes the upper sideband and blocks the lower

The carrier has already gone at the balanced modulator; the very narrow crystal filter passes only the upper sideband, 300 Hz to 3 kHz above 9 MHz, and rejects the lower. This is how the filter method makes SSB.

Variation of a filter’s attenuation within its passband

Passband ripple is the rise and fall of attenuation across the wanted passband that complex filters can show, not a single loss figure at its centre.

21,12 MHz

The nth harmonic is n times the fundamental, so the third is 3 × 7,04 = 21,12 MHz; 28,16 MHz, four times the fundamental, is the fourth harmonic.

Latches

Memory is built from latches, such as the D flip-flop; plain gates only combine their present inputs. Counters and shift registers are larger blocks made by joining flip-flops together.

15, 12, 10 and 6 m

The high bands are the top of HF and the bottom of VHF: about 15, 12, 10 and 6 m. The mid-bands run from about 40 m to 17 m, and the low bands are 160 to 60 m.

Inductive ones are added and capacitive ones subtracted

Inductive reactance counts as positive and capacitive as negative, so XTotal = XL1 + XL2 − XC1 − XC2. Both kinds of part have reactance. Swapping the signs gives the right size but calls an inductive total capacitive.

7 dB less

The bandwidth falls 2 700 ÷ 500 = 5,4 times, and so does the noise power: 10 log 5,4 = 7,3 dB less, nearest 7 dB less. Noise follows bandwidth, so it cannot stay unchanged.

300 mA

From P = V × I, I = P ÷ V = 1,8 ÷ 6 = 0,3 A, which is 300 mA. Dividing the other way, 6 ÷ 1,8 = 3,3, gives the 3,3 A slip.

6 cells

Each lead-acid cell gives about 2 V, so 12 ÷ 2 = 6 cells in series. Eight cells would suit 1,5 V torch cells, which a car battery does not use.

1 ms

The period is 1 ÷ 250 = 4 ms, and the peak comes a quarter cycle (90°) after the rising zero crossing: 1 ms. At 2 ms, half a cycle, it is back at zero; 0,64 ms comes from 2πft = 1.

105 W

At 100% modulation the sidebands add half the carrier power: 70 + 35 = 105 W, two-thirds of it in the carrier. Adding a third of the carrier instead gives 70 + 23,3 = 93 W.

Along the line from A towards B

Waves from A reach B a quarter cycle later, just as B’s lagging current catches up, so they add towards B; waves from B reach A 180° out of phase and cancel, giving a cardioid aimed from A to B.

A third digit of the value

The extra band gives a third digit, so the value can be stated more precisely; the multiplier and the tolerance band follow as before, so there is still only one tolerance band.

2,5 km

330 m/s × 8 s = 2 640 m, so 2,5 km is nearest; the manual likewise rounds 5 s to about 1,5 km (exactly 1,65 km). Dividing 330 by 8 gives the 40 m slip.

−12 dB

10 log₁₀ 0,07 = −11,5 dB, between −13 dB for 0,05 and −10 dB for 0,1, so −12 dB is nearest; 20 log 0,07 would give about −23 dB.

Water pressure and rate of flow

Voltage is like the pressure a pump creates, and current like the rate of flow it drives, such as litres per second; 'rate of flow and water pressure' swaps them.

To keep strong nearby signals out of the second mixer

The roofing filter rejects strong signals close enough to pass the preselector that could cause intermodulation or images in the second mixer. The final SSB selectivity comes from a narrower filter at the second IF.

Its 32 codes were too few for every letter, figure and punctuation sign

Five bits give only 2⁵ = 32 codes, too few for 26 letters, 10 figures and punctuation, so each code means a letter or a figure according to the shift. Baudot has no small letters.

To carry off the heat they produce while in use

All of the transmitter’s output turns into heat in the resistor, so big loads need fins, fans, oil or a mix of these. A plain resistor needs no tuning for each band, and it stores nothing.

Positive to the P-type side, negative to the N-type side

Forward bias puts positive on the P side and negative on the N side, pushing carriers into the depletion layer so that current flows once the forward bias voltage is exceeded. The other way round is reverse bias.

140 mA

XC = 1 ÷ (2π × 400 × 4,7 × 10⁻⁶) = 84,7 Ω, and I = 12 ÷ 84,7 = 0,142 A = 142 mA, nearest 140 mA. Reading µF as nF gives a thousand times less, 140 µA.

72°

The period is 1 ÷ 2000 = 0,5 ms, so B is 0,1 ÷ 0,5 = 0,2 of a cycle later: 0,2 × 360° = 72°. Multiplying 0,1 by 360 without dividing by the period gives 36°.

Energy the current releases in the semiconductor

With suitably chosen semiconductor material and doping, the energy change at the junction is given off directly as electromagnetic energy, which can be light. It is not glowing from heat, as a lamp filament does.

It reverses and opposes the reduction

While the supply raises the current, the induced voltage opposes the rise; once it starts to reduce the current, the induced voltage reverses so that it still opposes the change, now trying to keep the current up.

The voltage across the coil

The voltage leads, so it peaks first and the current follows a quarter of a cycle later. In a capacitor it is the other way round: the current peaks first.

125 Bd

Signalling rate = 1 ÷ pulse length = 1 ÷ 0,008 s = 125 Bd. Reading 8 ms as 8 Bd confuses the time of one pulse with the number of pulses each second.

The resistance of the conductor

The current depends on the voltage and on the conductor's resistance: the more resistance, the less current; insulation only keeps the current where it belongs, so its thickness does not set the current.

To weaken the unwanted harmonics further

Tuned to the output frequency, L2-C3 further weakens the harmonics left after L1-C1, such as three and four times the input. It is a filter; a stage that oscillated would be useless as a multiplier.

Practically none

With base and emitter joined, VBE is zero, well below the 600 mV needed, so no base current flows and IC = β × 0 = 0: the transistor is shut off. Shorting them never turns it on.

2,8 V

Vout = 9 × 680 ÷ (1500 + 680) = 6120 ÷ 2180 = 2,81 V, nearest 2,8 V. 4,1 V divides by R1 alone instead of R1 + R2, and 6,2 V is the share across R1.

3300 pF

A microfarad is 1 000 000 pF, so 0,0033 µF × 1 000 000 = 3300 pF; 330 pF has one zero too few.

100 Ω

n = 1 mA ÷ 200 µA = 5, so RS = 390 ÷ (5 − 1) = 97,5 Ω, nearest 100 Ω. 80 Ω is close to 390 ÷ 5 = 78 Ω: n used instead of n − 1.

Up to about 5/8 λ, they still give a good pattern

A longer vertical has a higher radiation resistance, helping against a poor ground, and its pattern stays good up to about 5/8 λ, hence the popular 5/8 λ mobile whips. Beyond that, performance deteriorates.

The doping of its channel: N-type or P-type

FETs come in two basic types, named after the semiconductor type of the drain-source channel: N-type or P-type. The supply polarity follows from the type but does not name it.