순시대역폭 (instantaneous bandwidth)

순시(瞬時) 대역폭 : 한번에 측정할 수 있는 대역폭
 

Tunable bandwidth versus instantaneous bandwidth
 

Instantaneous bandwidth is what you get with a receiver when you keep the LO at a fixed frequency, and sweep the input frequency to measure the response. The resulting bandwidth is a function of the frequency responses of everything in the chain: the preselector filter, low noise amp, the mixer, the IF amp and any filters that you have. Their instantaneous bandwidth has a direct effect on the minimum detectable signal.

Tunable bandwidth implies that you are allowed to change the frequency of the LO to track the RF frequency. The bandwidth in this case is only a function of the preselector filter, the LNA and the mixer. Tunable bandwidth is often many times greater than instantaneous bandwidth.


Instantaneous bandwidth: this is a measure of how wide a spectrum a system can respond to, without any type tuning. Using the analogy of radio, the IF bandwidth in an American FM receiver is about 200 kHz, which is necessary to pass the full spectrum of a broadcast FM signal. The demodulator processes this bandwidth to obtain the approximately 18 kHz baseband bandwidth. The "despreading" effect of this processing results in the superior signal to noise ratio enjoyed by FM transmission.