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The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal. Indeed. The notch filter in the transmit side is instead to protect the receiver from the transmitter. As well as the familiar harmonics and spur signals generated on specific frequencies by the transmitter it also produces broadband noise centred on ...


2

In the absence of test equipment there is no way to know for certain what went wrong, or what to do about it. The duplexer sounds like the most likely culprit, but the problem could be something else, like inadequate shielding in the receiver. If you ask around, maybe someone in your area has the necessary test equipment and wouldn't mind helping.


1

The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal. Perhaps not, but consider: The transmitter makes broadband noise and intermodulation products that may fall on the receive frequency. More isolation is better. And, The transmitter should ideally also not load the antenna at the receive frequency. ...


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