In VHF spectrum Analyzer, two types of frequency instabilities which will cause difficulties when narrow frequency range are displayed are known as (a) Short-term instability (b) Phase-noise (c) Correlation-noise (d) Long-term instability Choose the correct option

In VHF spectrum Analyzer, two types of frequency instabilities which will cause difficulties when narrow frequency range are displayed are known as (a) Short-term instability (b) Phase-noise (c) Correlation-noise (d) Long-term instability Choose the correct option Correct Answer (b) and (d)

Phase Noise:

• This noise can mask or block the narrow or close-in (to a carrier), low-level signals that might otherwise be visible.
• Phase noise is specified in terms of dB relative to a carrier and is displayed only when the signal is far enough above the system noise floor.
• This becomes a major limitation in an analyzer's ability to resolve signals of unequal amplitude. The below figure shows us that the phase noise actually covers up the smaller signal.

• Frequency Stability does not specify how much frequency is accurate, but how much it is stable during the observed time interval.
• If the considered time interval is up to 100 seconds (10 ms, 100 ms, 1 s, etc.), the stability analysis is termed as short-term stability.
• Otherwise, there is an analysis of long-term stability, and then we specify the oscillator’s stability for an hour, and more often for a day, a month, or a year.
• Long term instability causes difficulties when the narrow frequency range are displayed.