Properties of RadioWaves 1

Phase Comparison

Some radio navigation systems use the comparison of phase between two signals to define navigational information. The first important point is that the two signals being compared must have the same frequency, otherwise any phase comparison would be meaningless. The second point is that one signal will be designated the reference signal and the other a variable signal and that the comparison must yield a positive result.

Properties of Radio Waves 1

Figure 1.4 Sinusoidal wave - phase comparison

To determine the phase difference between 2 signals, first identify the position of (for example) zero phase on each of the waves, then move in the positive direction from the chosen point on the reference wave to measure the phase angle through which the reference wave has travelled before zero phase is reached on the variable wave.

In this example, starting at zero phase on the reference wave (point A), we observe that the reference wave has travelled through a phase angle of 270° before zero phase is reached on the variable wave (point B), hence the phase difference is 270°.

The relationship can also be found mathematically. At the origin the phase of the reference wave is 0° (= 360°) and the phase of the variable wave is 090°. Subtracting the instantaneous phase of the variable wave from the instantaneous phase of the reference wave gives the same result, note the result must always be positive.

Reference – variable = 360° – 90° = 270°

Note: The phase difference must be positive, so if the calculation yields a negative result simply add 360° to get a positive answer.

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1 Properties of RadioWaves

Waves Radio of Properties 1

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Questions 1

Practice Frequency (f) - Wavelength (λ) Conversions

In each of the following examples, calculate the frequency or wavelength as appropriate and determine in which frequency band each of the frequencies lies.

	Wavelength	Frequency	Frequency Band
1		198 kHz
2	2.7 m
3		5.025 GHz
4	137.5 m
5		137.5 MHz
6	3 km
7		329 MHz
8	29 cm
9		500 kHz
10	5 cm

Questions 1

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1 Answers

Answers 1

Answers to Practice Frequency (f) - Wavelength (λ) Conversions

	Wavelength	Frequency	Frequency Band
1	1515 m	198 kHz	LF
2	2.7 m	111.1 MHz	VHF
3	5.97 cm	5.025 GHz	SHF
4	137.5 m	2181.8 kHz	MF
5	2.18 m	137.5 MHz	VHF
6	3 km	100 kHz	LF
7	91.2 cm	329 MHz	UHF
8	29 cm	1034 MHz	UHF
9	600 m	500 kHz	MF
10	5 cm	6 GHz	SHF

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