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Question
An audio signal of 15kHz frequency cannot be transmitted over long distances without modulation because ______.
- the size of the required antenna would be at least 5 km which is not convenient.
- the audio signal can not be transmitted through sky waves.
- the size of the required antenna would be at least 20 km, which is not convenient.
- effective power transmitted would be very low, if the size of the antenna is less than 5 km.
Options
a, b and c
c, d and a
a, b and d
d, b and c
Solution
a, b and d
Explanation:
Size of the antenna or aerial. For transmitting a signal, we need an antenna or an aerial. This antenna should have a size comparable to the wavelength of the signal (at least 1/4 in dimension) so that the antenna properly senses the time variation of the signal. For an electromagnetic wave of frequency 20 kHz, the wavelength λ is 15 km. Obviously, such a long antenna is not possible to construct and operate. Hence direct transmission of such baseband signals is not practical. We can obtain transmission with reasonable antennas if the transmission frequency is high (for example,
if n is 1 MHz, then λ is 300 m). Therefore, there is a need of translating the information contained in our original low-frequency baseband signal into high or radio frequencies before transmission.
Effective power radiated by an antenna: A theoretical study of radiation from a linear antenna (length l) shows that the power radiated is proportional to (1/λ)2. This implies that for the same antenna length, the power radiated increases with decreasing λ, i.e., increasing frequency. Hence, the effective power radiated by a long wavelength baseband signal would be small. For a good transmission, we need high powers and hence this also points out the need of using high-frequency transmission.
| Time | Transcript |
| 00:00 - 00:59 | hello everyone let's look at this question it says an audio signal of 15 kHz frequency cannot be transmitted over a long distance without modulation because option one is the size of the required antenna would be at least 5 km which is not a convenient option to is the audio signal cannot be transmitted through Skyway option 3 is the size of the required in Tina would be at least 20 km which is not convenient and option 4 is effective power transmitted would be very low If the size of the antenna less than 5 km the latest find this out where are given with frequency of the Waves to be transmitted so VM is equal to 3 kHz this if we change it into words would be 15 into 10 to the power 3 |
| 01:00 - 01:59 | wavelength Lambda is equal to see upon VM this will be equal to 3 into 10 to the power 8 upon 3 into 10 to the power 3 which will be equal to 1.5 into 10 to the power 5 in M now this means the size of the antenna will be equal to that would be required will be equal to L equal to Lambda upon 4 this will be equal to 1 upon 4 of Lambda that we just found out to be equal to 1.5 into 10 to the power 5 so this will give me equal to 5 into 10 to the power 3 that means in kilometres it would be fine |
| 02:00 - 02:59 | km right now we also need to respond according to the options that are given to us above so we know the audio signal audio signals are low frequency write their low-frequency waves so that they cannot be transmitted through Skype because they will be then absorbed by the atmosphere so if the size of the antenna is less than 5 If the size is the size of antenna is less than this 5km then what will happen the effective power transmission then the effective power |
| 03:00 - 03:59 | the transmission would be very long would be very low because of deviation from resonance wavelength of wave and and and and and in a length that means the correct options are options one which is the size of the required and in a would be at least 5 km right then option to also because if there is the audio signal cannot be transmitted through Skywaves and option 3 se the size of the antenna required would be at least 20 km this is not correct this is wrong and option forest effective power transmitted would be very low If the size of the antenna is less than 5 km that means option 4 is also correct of you understood this question |
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