Editing Antenna analyzer (section)

===Antenna bridge===
[[Image:Antennabridge.png|250px|right|thumb|A typical antenna bridge, the [[trimmer (electronics)|trimmer]] capacitor ({{mvar|C}}) is adjusted to make the bridge balance when the variable [[capacitor]] on the left is half meshed. Hence the bridge will be able to detect if an [[Antenna (radio)|antenna]] is either a capacitive or inductive load.]]A [[bridge circuit]] has two legs which are [[frequency]]-dependent [[complex number|complex]]-valued [[Electrical impedance|impedance]]s. One leg is a circuit in the analyzer with calibrated components whose combined impedance can be read on a scale. The other leg is the ''unknown'' – either an antenna or a [[Electrical reactance|reactive]] component.

To measure impedance, the bridge is adjusted, so that the two legs have [[impedance matching|the same impedance]]. When the two impedances are the same, the bridge is balanced. Using this circuit it is possible to either measure the impedance of the antenna connected between ANT and GND, or it is possible to adjust an antenna, until it has the same impedance as the network on the left side of the diagram below. The bridge can be driven either with ''white noise'' or a simple carrier (connected to drive). In the case of white noise the [[amplitude]] of the exciting signal can be very low and a radio receiver used as the detector. In the case where a simple carrier is used then depending on the level either a [[diode]] detector or a receiver can be used.<ref name=Carr-1999>{{cite book |first=Joseph J. |last=Carr |date=11 December 2000 |chapter=Chapter&nbsp;17 Building and using an RF noise bridge |title=Secrets of RF Circuit Design |edition=3rd |page=319 |publisher=McGraw-Hill / TAB Electronics |isbn=0-07-137067-6 |postscript=,}} {{ISBN|978-0071370677}}</ref> In both cases a [[null (mathematics)|null]] will indicate when the bridge is balanced.