Talk:Active antenna

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Description Misses the Mark

". . . used in situations where a larger passive antenna is either impractical (inside a portable radio) . . ."

This example of a portable radio makes no sense. Where an antenna is integrated into a portable radio, how is one to distinguish an active antenna from a passive antenna driving the receiver's RF amplifier?

". . . or impossible (suburban residential area that disallows use of large outdoor low-frequency antennas)."

While this example is more plausible, it's not commonly done.

Where active antennas ARE commonly used is in situations where transmission line loss from the antenna to receiver would degrade system noise figure. This typically means UHF/microwave systems and includes essentially all satellite receivers.

"The signal attenuation caused by the antenna-size-to-wavelength mismatch . . ."

There is no attenuation caused by antenna size-to-wavelength mismatch. A given antenna topology has the exactly and identically same directivity and, ignoring resistive losses, the same gain whether it's full size or infinitesimally small. There IS inefficiency due to loss resistances overshadowing the very low radiation resistance of a small antenna.

"The [nonexistent] signal attenuation . . . is compensated by the active circuit."

This would be true in a world with no KTB noise, but it's not true in the real world. The only situation in which an antenna amplifier can compensate for poor antenna efficiency is in extremely noisy electromagnetic environments, such as LF reception, where received atmospheric noise is thousands of times greater than KTB, such that the signal to noise ratio is not degraded by antenna inefficiency. Otherwise, an antenna just amplifies KTB noise by the same factor as the signal, improving nothing.

While active antennas are useful in a wide range of applications, including some of the ones described here, the most common example (overcoming transmission line loss) is missing, and the explanations in this article are just plain wrong. — Preceding unsigned comment added by 137.79.192.124 (talk) 17:51, 19 November 2018 (UTC)[reply]