Binary ASK modulation gives ST1 : High noise immunity
ST2 : Large bandwidth
ST1 and ST2 are wrong.
Neither claim survives examination — ASK has the worst noise immunity of the digital schemes and the narrowest bandwidth, option 3.
ST 1 — noise immunity is ASK's weakness, not its strength. Amplitude is precisely the quantity that noise corrupts: thermal noise adds directly to the received amplitude, so a noise burst can push a "0" above the decision threshold or drag a "1" below it. Nothing can be done at the receiver to separate the two, because the information and the interference live in the same dimension. FSK and PSK both keep the envelope constant, which is why a limiter can strip amplitude noise from them before detection — an option ASK does not have. The error probabilities make the ranking explicit:
| Scheme | Coherent Pe | Relative Eb/N0 |
|---|---|---|
| ASK | \(Q\left(\sqrt{\dfrac{E_{b}}{N_{0}}}\right)\) | Worst |
| FSK | \(Q\left(\sqrt{\dfrac{E_{b}}{N_{0}}}\right)\) | Same, but constant envelope |
| PSK | \(Q\left(\sqrt{\dfrac{2E_{b}}{N_{0}}}\right)\) | 3 dB better |
ST 2 — the bandwidth claim is also wrong, and in the opposite direction. On-off keying is simply the carrier multiplied by a baseband pulse train, so its spectrum is that pulse train's spectrum translated to the carrier:
\(BW_{ASK}=2R_{b}\)
That is the same as PSK and less than FSK, which must additionally accommodate the frequency shift:
\(BW_{FSK}=2\left(\Delta f+R_{b}\right)\)
So ASK is among the most bandwidth-efficient of the three, not the least. Calling its bandwidth "large" inverts the comparison.
What ASK does have to recommend it is simplicity: an on-off switch generates it and an envelope detector recovers it, needing no carrier recovery at all. That is why it survives where noise is not the limiting factor — in optical fibre links, where on-off keying is the standard modulation, and in low-cost infrared and RFID systems.
Flagged because "large bandwidth" is a comparative claim with no stated reference; but against its two natural rivals, ASK is no wider than PSK and narrower than FSK.
Hence, both statements are wrong.
Similar Questions
Which of the following digital modulation systems support high bit rate ?
In coherent binary FSK system the orthogonal sinusoidal signals of frequency 20 kHz and 50 kHz are used to represent '0' and '1' respectively. The maximum possible bit interval is:
Which of the following statements are correct :
(a) ASK gives a maximum probability of error.
(b) FSK is also known as ON-OFF keying.
(c) In DPSK, no synchronous carrier is needed at the receiver.
(d) Probability of Error in DPSK is less than BPSK.
Important Questions from Introduction To Digital Modulation
In digital data transmission, a line code should have the following properties
(A) Transmission bandwidth should be as small as possible
(B) Transmitted power should be as high as possible
(C) Transmission bandwidth should be as high as possible
(D) Transmitted power should be as low as possible
Choose the correct answer from the options given below:
If the in‐phase and quadrature components in an M‐ary PSK system are permitted to be independent, then this scheme becomes a:
Which of the following statements are correct?
A. M‐ary modulation scheme is preferable where the bandwidth requirement is important.
B. M‐ary PSK system considers 'M' different phases in the range 'π/2'.
C. In M‐ary modulation scheme, only coherent detection is possible.
D. M‐ary QAM scheme uses 'm 2' carrier signals having the same frequency.
Choose the correct answer from the options given below:
In digital communication, Inter Symbol Interference (ISI) is a form of distortion where one symbol interferes with subsequent symbols. An eye diagram is used to study the extent of ISI in a communication channel. Which of the following is FALSE?
The data rate of QPSK is ______ as that of BPSK for the same symbol rate.
