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I read FDD has separate Rx and TX frequency to operate on, so it can work simultaneously and do Receive and Transmission. When I use Duplexer ( I read Duplexer needed if we want a single antenna to do both Rx and TX details here https://www.google.com/amp/www.techplayon.com/duplexer-used-advantages-disadvantages/amp/ ), so doesn't the use of Duplexer limits FDD to either do Rx or TX at a time. Which is similar to TDD (even though in TDD Freq is same). Does switching of Rx and Tx paths in Duplexer for FDD, faster than switching of Rx and Tx process at same frequency in TDD.

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  • $\begingroup$ If you mean duplexer and not diplexer please edit your question to provide a link to what you're talking about. $\endgroup$
    – TimWescott
    Nov 14, 2021 at 0:42
  • $\begingroup$ Done added the link $\endgroup$ Nov 14, 2021 at 10:05
  • $\begingroup$ Are your Tx and Rx frequencies on the same actual channel or just close to each other? For example: cellular basestation band 1850-1910 MHz for receive and 1930-1990 MHz for transmit, I have implemented such base-station designs with a diplexer to a single antenna that would separate and isolate the Tx and Rx paths. $\endgroup$ Nov 14, 2021 at 23:42
  • $\begingroup$ So you mean that if frequency are close we can use Diplexer? And what if they are at a gap and one is of Rx and one of Tx? Can you please share insight on what you made and how $\endgroup$ Nov 28, 2021 at 6:58

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What that article is calling a "duplexer" is normally (according to Wikipedia, and to my experience with radio installations in the 1990's) called a "diplexer". So if you're searching around for information, you probably want to include "diplexer" in your search.

The problem with frequency-division or code-division multiplexing is that simplistic theory and actual practice don't match. In theory, a receiver won't respond to transmitted signals that are sufficiently far away (in frequency or code-space). In practice, a receiver's front-end circuitry can be overloaded by the transmitted signal.

For frequency-division multiplexing, enter the diplexer.

A well-designed diplexer isolates the receiver from the transmitter, such that the transmitter signal is significantly attenuated (by as much as 60 or 80dB) at the receiver antenna. This is generally done with a combination of high-quality notch filters at the transmitter frequency, and band-pass filters at the receive frequency. The result of this is that the transmitter can transmit without stomping on the receiver's front end, and effective communication can be affected.

For more detail -- possibly more than you want -- search on "radio repeater". This should get you a lot of information about the traditional voice-band radio repeater technology that makes heavy use of diplexers in most circumstances.

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  • $\begingroup$ Hi Tim, I read Diplexer takes two different Freq signal having sufficient gap between them and can multiplex them and can do vice versa. Duplexer is used when we have a single antenna and want to use it both for Rx and Tx operating at frequency which are close to each other. Am I wrong? Actually I meant Duplexer only here not Diplexer. My doubt is whether at same time this both Rx and Tx can be done together using same antenna? Please guide. $\endgroup$ Nov 13, 2021 at 22:28

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