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A low-noise amplifier (LNA) is an electronic component that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio (SNR). Any electronic amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise.
The low-noise quality of an LNB is expressed as the noise figure (or sometimes noise temperature). This is the signal-to-noise ratio at the input divided by the signal-to-noise ratio at the output. It is typically expressed as a decibels (dB) value. The ideal LNB, effectively a perfect amplifier, would have a noise figure of 0 dB and would not ...
An RF amplifier, often called the low-noise amplifier (LNA). Its primary responsibility is to increase the sensitivity of the receiver by amplifying weak signals without contaminating them with noise, so that they can stay above the noise level in succeeding stages. It must have a very low noise figure (NF). The RF amplifier may not be needed ...
There are a number of RF amplifier tubes that operate in a similar fashion to the TWT, known collectively as velocity-modulated tubes. The best known example is the klystron. All of these tubes use the same basic "bunching" of electrons to provide the amplification process, and differ largely in what process causes the velocity modulation to occur.
The f c for an amplifier depends on the actual configuration used, because radio-frequency and low-frequency negative feedback can have an effect on f c. So for accurate results, f c must be determined from added noise measurements on the amplifier using R.F., with the actual circuit configuration to be used in the oscillator.
The RF signal from the antenna may have one stage of amplification to improve the receiver's noise figure, although at lower frequencies this is typically omitted. The RF signal enters a mixer , along with the output of the local oscillator , in order to produce a so-called intermediate frequency (IF) signal.
Parametric amplifiers are used in applications requiring extremely low noise. A parametric oscillator is a driven harmonic oscillator in which the oscillations are driven by varying some parameters of the system at some frequencies, typically different from the natural frequency of the oscillator.
For this reason, the first stage amplifier in a receiver is often called the low-noise amplifier (LNA). The overall receiver noise "factor" is then The overall receiver noise "factor" is then F r e c e i v e r = F L N A + F r e s t − 1 G L N A {\displaystyle F_{\mathrm {receiver} }=F_{\mathrm {LNA} }+{\frac {F_{\mathrm {rest} }-1}{G_{\mathrm ...
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