How does a duplexer isolate RX from TX? How is the correct duplexer determined for a particular application? Does close frequency spacing require more and larger cavities than wide spacing?
Thanks y'all...
DUPLEXERS
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There isn't a simple answer to this question. In the most simple terms, a duplexer is a set of filters that passes only the frequency of interest and rejects any others. This tends to keep the xmit frequency out of the receiver while allowing it to pass to the antenna, and allows the received frequency to pass to the receiver while keeping it and the receiver's own generated signal out of the transmitter.
Designs will differ in the amount of attentuation you get (100 dB is considered the minimum for a base station while as little as 40 is used in some mobile duplexers) and the sharpness of the "filter" skirts -- i.e, how quickly the attentuation kicks in as you begin to move away from the tuned frequency. The closer the input and output frequencies are to one another, the greater the isolation and sharper the skirts you will need, which generally increases cost, physical size and insertion loss, often drastically.
Designs will differ in the amount of attentuation you get (100 dB is considered the minimum for a base station while as little as 40 is used in some mobile duplexers) and the sharpness of the "filter" skirts -- i.e, how quickly the attentuation kicks in as you begin to move away from the tuned frequency. The closer the input and output frequencies are to one another, the greater the isolation and sharper the skirts you will need, which generally increases cost, physical size and insertion loss, often drastically.
