15.1 Radio Beacon Goniometric Radio Navigation Systems
281
(electronic goniometer method), at which a rotation effect of ADP is achieved by
supplying of two mutually perpendicular beamed antennas with patterns in shape of
eight. Antenna supply is provided via balance-modulated oscillations with dephased
modulation at 90°.
For shaping of a signal with double amplitude-frequency modulation, the oscillations are selected, the frequency of which is considerably more than ADP rotation rate (frequency), but considerably lower than carrier wave frequency, and these
oscillations are used as an auxiliary. Auxiliary oscillations are called subcarrier, for
which a condition subc ω 0 should be fulfilled, where subc —frequency of
subcarrier oscillations. For VOR system, a subcarrier frequency equals to 9960 Hz.
In subcarrier modulator (SM), a frequency modulation of subcarrier is provided,
by reference oscillations of 30 Hz with frequency deviation of 480 Hz at modulation
index—16. In modulator (HFM), the high-frequency oscillations are modulated in
amplitude by subcarrier voltage with modulation depth of 30%.
Antenna A 1 set up a field with density
e 1 (t) = E 1M
1 + m am cos
subc t +
subc
cos t
cos ω 0 t,
(15.9)
where m am —amplitude modulation coefficient (factor);
subc
—frequency modulation coefficient; subc —subcarrier frequency deviation.
The summary effects on antenna of onboard equipment A 0 . We have a summary
oscillation at the output of antenna:
u (t) = K U M Z cos ω 0 t,
Z = 1 + m c cos(t − θ) + m am cos
subc t +
subc
cos t
. (15.10)
Amplitude-frequency spectrum of summary oscillation is shown in Fig. 15.3.
It is necessary to extract from a summary for onboard equipment the azimuthal
and reference signals and implement its comparison in phase.
After resultant (sum) signal conversion in receiving unit (Rcv), its amplifying and
detection by amplitude detector (demodulator), an envelope is produced containing
an azimuthal and reference signals of the following form:
u env (t) = U 2M cos(t − θ) + U 1M cos
subc t +
subc
cos t
(15.11)
where U 1M and U 2M —amplitudes of composite signal components.
From Fig. 15.3, we can see that azimuthal and reference signals can be extracted
via frequency discrimination (selection). For this purpose, from Rcv output the signal
is delivered to two filters F1 and F2. In F1 filter, adjusted on 30 Hz frequency,
azimuthal signal is extracted or variable phase signal, and in F2 filter, adjusted on
9960 Hz subcarrier frequency, the frequency-modulated under carrying oscillation
281
(electronic goniometer method), at which a rotation effect of ADP is achieved by
supplying of two mutually perpendicular beamed antennas with patterns in shape of
eight. Antenna supply is provided via balance-modulated oscillations with dephased
modulation at 90°.
For shaping of a signal with double amplitude-frequency modulation, the oscillations are selected, the frequency of which is considerably more than ADP rotation rate (frequency), but considerably lower than carrier wave frequency, and these
oscillations are used as an auxiliary. Auxiliary oscillations are called subcarrier, for
which a condition subc ω 0 should be fulfilled, where subc —frequency of
subcarrier oscillations. For VOR system, a subcarrier frequency equals to 9960 Hz.
In subcarrier modulator (SM), a frequency modulation of subcarrier is provided,
by reference oscillations of 30 Hz with frequency deviation of 480 Hz at modulation
index—16. In modulator (HFM), the high-frequency oscillations are modulated in
amplitude by subcarrier voltage with modulation depth of 30%.
Antenna A 1 set up a field with density
e 1 (t) = E 1M
1 + m am cos
subc t +
subc
cos t
cos ω 0 t,
(15.9)
where m am —amplitude modulation coefficient (factor);
subc
—frequency modulation coefficient; subc —subcarrier frequency deviation.
The summary effects on antenna of onboard equipment A 0 . We have a summary
oscillation at the output of antenna:
u (t) = K U M Z cos ω 0 t,
Z = 1 + m c cos(t − θ) + m am cos
subc t +
subc
cos t
. (15.10)
Amplitude-frequency spectrum of summary oscillation is shown in Fig. 15.3.
It is necessary to extract from a summary for onboard equipment the azimuthal
and reference signals and implement its comparison in phase.
After resultant (sum) signal conversion in receiving unit (Rcv), its amplifying and
detection by amplitude detector (demodulator), an envelope is produced containing
an azimuthal and reference signals of the following form:
u env (t) = U 2M cos(t − θ) + U 1M cos
subc t +
subc
cos t
(15.11)
where U 1M and U 2M —amplitudes of composite signal components.
From Fig. 15.3, we can see that azimuthal and reference signals can be extracted
via frequency discrimination (selection). For this purpose, from Rcv output the signal
is delivered to two filters F1 and F2. In F1 filter, adjusted on 30 Hz frequency,
azimuthal signal is extracted or variable phase signal, and in F2 filter, adjusted on
9960 Hz subcarrier frequency, the frequency-modulated under carrying oscillation