Sample Exam 1

A good frequency counter is accurate as ± 1 Hz. When using an Oscilloscope we have to measure the wave length according to scale on the screen an calculate the frequency. The error will be about 10%. An absorption wave meter has an analog dial, it operates by extracting a small amount of energy from the oscillating circuit to be measured. Because of that the error will be more ( about 10%) .

VLF (very low frequency) = 10 to 30 kHz. ; LF (low frequency or long wave) = 30 to 300 kHz. ; MF (medium frequency or medium wave) = 300 to 3000 kHz. ; HF (high frequency or short wave) = 3 to 30 MHz. ; VHF (very high frequency) = 30 to 300 MHz. ; UHF (ultra high frequency) = 300 to 3000 MHz. ; SHF (super high frequency) = 3 to 30 GHz. ; EHF ( extra high frequency or micro wave) = 30 to 300 GHz.

Apply P = V I, V = 24 Volt, I = 0.5 A, therefore P = 24 x 0.5 = 12 W

Variable capacitor is a tuning condenser or a varactor diode; Variable resistor is a potentiometer or variac or reostat; There is no meaning on variable regulator because regulator is a constant supply.

Apply the following formula for the reactance of capacitor, X = 1 / 2 π f C, When "f" increasing "X" is decreasing.

Apply X = 2 π f L = 2 x 3.14 x 50 x15 = 4700 Ω (approximately:- 2x3x50x15 = 4500)

Use the formula of P = V I, P = 3W, V = 12V, therefore I = P/V = 3/12 = 0.25 A = 250 mA

The best conductor is Silver, next copper, next gold , next aluminium. But silver and gold are too expensive for common use. That is why copper and aluminium are commonly used.

1 GHz = 1000 MHz

The unit of resistance is Ohm. The unit of current is Ampere. The unit of capacitance is Farad. The unit of power is Watt.

For two parallel resistors, Equivalent resistance is R = R₁ R₂ / (R₁ + R₂), therefore R = 100 x 150 / ( 100+150) = 100 x 150 / 250 = 60 Ω

As shown in the diagram, when a diode connected in series with an a.c. supply it’s a half wave rectification. If you connect a bridge rectifier with the a.c. supply it is Fullwave rectification. If a diode connected with a d.c. supply as forward bias, it is a reverse bias protection. That means, if you connect a d.c. supply with wrong polarity by mistake, protect your equipment. There is a special system to connect few diodes and capcitors with an a.c. supply you can multiply the voltage accordingly.

parallel connection of 33pF and 27pF is equivalent to 60 pF ( 33+27 =60), same way other two equivalent to 40 pF. Then these 60pF and 40 pF connected as series. Their equivalent value is 60x40 / (60+40) =24pF.

For silicon transistors, base-emitter bias voltage must be above 0.7 V. For germanium transistors, it is above 0.3 V. Same principle apply for diodes also.

The moving coil generates an electro-magnet ic field, while a current flow through the coil. This coil installed on a permanent magnetic field. This coil is turning (moving) due to the interaction between those fields.

SSB transmitter produces a DSB (Double Side Band) signal from the balanced modulator and passes through the side band filter for USB or LSB signal and the non selected side band gets filtered out.

If SWR equal to 1 (or 1:1) the antenna system is perfectly matched. If it is totally mismatched, SWR = infinity, If it is less than 2, it is practically acceptable. If it is 3, only 50% of power will radiate. Always SWR exist between 1 and infinity.

A good dummy load must have a pure resistance, without having a reactance. Only then will it have a 1:1 SWR. Wire wound resistors or electric bulbs have some reactance. But in practically, testing an amateur TX having about 50 Watts we can use a filament type bulb (100 W 230 V) as a dummy load.

If modulating index = 1, it is 100% modulated. If it slightly increased, it is over modulated. Then signal becomes distorted. Therefore always modulating index < 1

Two resistors of 110 Ohm are in parallel. It is equivalent to 55 Ohms. This 55 Ohm is connected in series with 5 Ohms. This is equivalent to 60 Ohms.

Apply P = V I formula. Therefore, P = 24 x 2.5 = 60W

Low pass filter is filtering only higher frequencies and it allow to pass low frequencies. Band pass filter allow to pass all frequencies within the specified frequency range. All lower frequencies and all higher frequencies get cut off. High pass filter stops all lower frequencies and allows to passing of higher values only. Notch filter cuts only one perticular frequency.

Use the formula, Z² = X² + R², Therefore Z² = 6² + 8² = 36 + 64 = 100, therefore Z = √100 = 10 Ohm.

apply the formula of, P = V I, V = 12V, I = 1.5 A, therefore, P = 12 x 1.5 = 18 Watt

Use the formula, P = I² R , P = 25W, R = 10000Ohm, Therefore I² = P / R = 25 / 10000. Therefore I = √( 25 / 10000) = 5 / 100 = 0.05 A or 50 mA

Apply P = I² R formula, I = 0.5 A, R = 70Ω Therefore P = 0.5 x 0.5 x 70 = 17.5 W

The question says accuracy, but it would have been better to say the error of the moving coil meter is about 3%. That means accuracy is 97%.

Consider R = ρ l / A formula, R = resistance, ρ = resistivity of the material, l = length of conductor, A = cross section of the conductor. The conductivity is increased by the decrease of the resistance, R. For decrease R; ρ and l should decrease or A should increase.

From a dip meter, frequency is measured with an analog dial. Error is not more than ±10% . It operates by extracting a very small amount of energy from the oscillating circuit to be measured.

Ground wave propagation occurs on MF (300kHz to 3MHz) and HF (3 to 30MHz) only. Above 30 MHz, propagate mostly with line of sight.

If the tolerance is 10% , The value is 4700±10%. 10% of 4700 is 470. Therefore 4700±10% is equals to 4700±470. Therefore 4700+ 470 = 5170 and 4700 - 470 = 4230.

Electric charges do not pass through a capacitor. Therefore it acts as a infinite resistor.

Voltmeter and Ammeter can't do anything on this. An absorption wave meter can use only if there is enough power output. But dip meter (dip oscillator or GDO) can measure the frequency in the oscillator circuit. It operates by extracting a very small amount of energy from the oscillating circuit to be measured.

The unit of Power is Watt. The unit of potential or voltage is Volt. The unit of current is Ampere. The unit of resistance is Ohm.

If the current through primary winding varies, a voltage is induced on the secondary. This action continues, only while an A.C. supply connected to the primary.

1. If you convert a moving coil meter to a voltmeter and measure the voltage across the resistor and calculate the power using P = V² / R. 2. If you convert a moving coil meter to an ammeter, measure the current through the resistor and calculate the power with using P = I² R 3. If you don't know the resistance, measure the voltage across the resistor and current through the resistor and calculate the power using, P = V I. Thermister is a special kind of resistor, it's resistance varies with the temperature. Thermocouple generates an electric current , when it is heating up. Thermostat is a switch operating according to the temperature.

Formula for the equivalent value of parallel capacitors is C = C₁ + C₂ + C₃ = 8+4+2 =14 μF